InfoAlly

Android: Adding easy share

2015-07-11T22:23:00.004+05:30

For implementing user friendly share in action bar is made easy.

Add Menu item as follows

<item    android:id="@+id/menu_item_share"    app:showAsAction="always"    android:title="Share"    android:icon="@drawable/abc_ic_menu_share_mtrl_alpha"    android:orderInCategory="3"    android:actionProviderClass=        "android.widget.ShareActionProvider" />

Update the share intent associated with that action item. Here's an example:


private ShareActionProvider mShareActionProvider;
...
@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate menu resource file.
    getMenuInflater().inflate(R.menu.share_menu, menu);

    // Locate MenuItem with ShareActionProvider
    MenuItem item = menu.findItem(R.id.menu_item_share);

    // Fetch and store ShareActionProvider
    mShareActionProvider = (ShareActionProvider) item.getActionProvider();

    // Return true to display menu
    return true;
}
// Call to update the share intent
private void setShareIntent(Intent shareIntent) {
    if (mShareActionProvider != null) {
        mShareActionProvider.setShareIntent(shareIntent);
    }
}

Using lists in Android (ListView) - Tutorial

2015-06-22T20:12:00.002+05:30

1. Android and Lists

1.1. Using lists in Android

The display of elements in a list is a very common pattern in mobile applications. The user sees a list of items and can scroll through them. Such an activity is depicted in the following picture.

Typically the user interacts with the list via the action bar, for example, via a refresh button. Individual list items can be selected. This selection can update the action bar or can trigger a detailed screen for the selection. The following graphic sketches that. On the selection of a list item another activity is started.

1.2. Views for handling lists

Android provides the ListView and the ExpandableListView classes which is capable of displaying a scrollable list of items.
The ExpandableListView class supports a grouping of items.

1.3. Possible input types for lists

The input to the list (items in the list) can be arbitrary Java objects. The adapter extracts the correct data from the data object and assigns this data to the views in the row of the ListView.
These items are typically called the data model of the list. An adapter can receive data as input.

1.4. Adapters

An adapter manages the data model and adapts it to the individual entries in the widget. An adapter extends the BaseAdapter class.
Every line in the widget displaying the data consists of a layout which can be as complex as you want. A typical line in a list has an image on the left side and two text lines in the middle as depicted in the following graphic.

A layout file for a such a line might look like the following.

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="?android:attr/listPreferredItemHeight"
    android:padding="6dip" >

    <ImageView
        android:id="@+id/icon"
        android:layout_width="wrap_content"
        android:layout_height="fill_parent"
        android:layout_alignParentBottom="true"
        android:layout_alignParentTop="true"
        android:layout_marginRight="6dip"
        android:contentDescription="TODO"
        android:src="@drawable/ic_launcher" />

    <TextView
        android:id="@+id/secondLine"
        android:layout_width="fill_parent"
        android:layout_height="26dip"
        android:layout_alignParentBottom="true"
        android:layout_alignParentRight="true"
        android:layout_toRightOf="@id/icon"
        android:ellipsize="marquee"
        android:singleLine="true"
        android:text="Description"
        android:textSize="12sp" />

    <TextView
        android:id="@+id/firstLine"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_above="@id/secondLine"
        android:layout_alignParentRight="true"
        android:layout_alignParentTop="true"
        android:layout_alignWithParentIfMissing="true"
        android:layout_toRightOf="@id/icon"
        android:gravity="center_vertical"
        android:text="Example application"
        android:textSize="16sp" />

</RelativeLayout>

The adapter would inflate the layout for each row in its getView() method and assign the data to the individual views in the row.
The adapter is assigned to the ListView via the setAdapter method on the ListView object.

Tip

Adapters are not only used by ListView, but also by other views which extend AdapterView as, for example, Spinner, GridView, Gallery and StackView.

1.5. Filtering and sorting

Filtering and sorting of the data is handled by the adapter. You need to implement the logic in your custom adapter implementation.

1.6. Data updates in the adapter

The notifyDataSetChanged() method on the adapter is called if the data has changed or if new data is available.
The notifyDataSetInvalidated() method is called if the data is not available anymore.

1.7. Listener

To react to selections in the list, set an OnItemClickListener to your ListView.

listView.setOnItemClickListener(new OnItemClickListener() {
  @Override
  public void onItemClick(AdapterView<?> parent, View view,
    int position, long id) {
    Toast.makeText(getApplicationContext(),
      "Click ListItem Number " + position, Toast.LENGTH_LONG)
      .show();
  }
});

2. Default adapter

2.1. Default platform adapter

Android provides default adapter implementations; the most important are ArrayAdapter and CursorAdapter.
ArrayAdapter can handle data based on Arrays or java.util.List.
SimpleCursorAdapter can handle database related data.

2.2. Using ArrayAdapter

The ArrayAdapter class can handle a list or array of Java objects as input. Every Java object is mapped to one row. By default, it maps the toString() method of the object to a view in the row layout.
You can define the ID of the view in the constructor of the ArrayAdapter otherwise the android.R.id.text1 ID is used as default.
The ArrayAdapter class allows to remove all elements in its underlying data structure with the clear() method call. You can then add new elements via the add() method or a Collection via the addAll() method.
You can also directly modify the underlying data structure and call the notifyDataSetChanged() method on the adapter to notify it about the changes in data.

Warning

If you want to change the data in your adapter, the underlying data structure must support this operation. This is, for example, the case for the ArrayList class, but not for arrays.

2.3. ListView example with ArrayAdapter

The following listing shows a layout file called activity_listviewexampleactivity.xml which includes a ListView.

<ListView xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/listview"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content" />

The following example shows the usage of the ListView view in an activity. It uses a default layout from the Android platform for the row layout. It also demonstrates the removal of list items and uses animations for the removal.

package com.vogella.android.listview.withanimation;

public class ListViewExampleActivity extends Activity {

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_listviewexampleactivity);

    final ListView listview = (ListView) findViewById(R.id.listview);
    String[] values = new String[] { "Android", "iPhone", "WindowsMobile",
        "Blackberry", "WebOS", "Ubuntu", "Windows7", "Max OS X",
        "Linux", "OS/2", "Ubuntu", "Windows7", "Max OS X", "Linux",
        "OS/2", "Ubuntu", "Windows7", "Max OS X", "Linux", "OS/2",
        "Android", "iPhone", "WindowsMobile" };

    final ArrayList<String> list = new ArrayList<String>();
    for (int i = 0; i < values.length; ++i) {
      list.add(values[i]);
    }
    final StableArrayAdapter adapter = new StableArrayAdapter(this,
        android.R.layout.simple_list_item_1, list);
    listview.setAdapter(adapter);

    listview.setOnItemClickListener(new AdapterView.OnItemClickListener() {

      @Override
      public void onItemClick(AdapterView<?> parent, final View view,
          int position, long id) {
        final String item = (String) parent.getItemAtPosition(position);
        view.animate().setDuration(2000).alpha(0)
            .withEndAction(new Runnable() {
              @Override
              public void run() {
                list.remove(item);
                adapter.notifyDataSetChanged();
                view.setAlpha(1);
              }
            });
      }

    });
  }

  private class StableArrayAdapter extends ArrayAdapter<String> {

    HashMap<String, Integer> mIdMap = new HashMap<String, Integer>();

    public StableArrayAdapter(Context context, int textViewResourceId,
        List<String> objects) {
      super(context, textViewResourceId, objects);
      for (int i = 0; i < objects.size(); ++i) {
        mIdMap.put(objects.get(i), i);
      }
    }

    @Override
    public long getItemId(int position) {
      String item = getItem(position);
      return mIdMap.get(item);
    }

    @Override
    public boolean hasStableIds() {
      return true;
    }

  }

}

3. Custom adapter implementations

3.1. Developing a custom adapter

The ArrayAdapter is limited as it supports only the mapping of toString() to one view in the row layout. To control the data assignment and to support several views, you have to create your custom adapter implementation.
For this you would extend an existing adapter implementation or subclass the BaseAdapter class directly.

Tip

Frequently you extend ArrayAdapter to write a custom adapter, as this is simpler than extending BaseAdapter directly.

3.2. Preparing a row for the list

The adapter needs to create a layout for each row of the list. The ListView instance calls the getView() method on the adapter for each data element. In this method the adapter creates the row layout and maps the data to the views in the layout.
This root of the layout is typically a ViewGroup (layout manager) and contains several other views , e.g., an ImageView and a TextView. The following graphic shows a list with different layouts for odd and even rows.

Within the getView() method you would inflate an XML based layout and then set the content of the individual views based on the Java object for this row. To inflate the XML layout file, you can use the LayoutInflator system service.

Note

This layout inflator service can get accessed via the getLayoutInflator() method of the activity or via the

context.getSystemService(Context.LAYOUT_INFLATER_SERVICE)

method call.

After the adapter inflated the layout, it searches for the relevant views in the layout and fills them with the data. The individual elements in the layout can be found via the findViewById() method call on the top level view.

3.3. Example for a custom adapter

The following code shows an implementation of a custom adapter. This adapter assumes that you have two png files (no.png and ok.png) in one of your res/drawable folders. The coding inflates an XML layout file, finds the relevant views in the layout and sets their content based on the input data.

package de.vogella.android.listactivity;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.TextView;

public class MySimpleArrayAdapter extends ArrayAdapter<String> {
  private final Context context;
  private final String[] values;

  public MySimpleArrayAdapter(Context context, String[] values) {
    super(context, -1, values);
    this.context = context;
    this.values = values;
  }

  @Override
  public View getView(int position, View convertView, ViewGroup parent) {
    LayoutInflater inflater = (LayoutInflater) context
        .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    View rowView = inflater.inflate(R.layout.rowlayout, parent, false);
    TextView textView = (TextView) rowView.findViewById(R.id.label);
    ImageView imageView = (ImageView) rowView.findViewById(R.id.icon);
    textView.setText(values[position]);
    // change the icon for Windows and iPhone
    String s = values[position];
    if (s.startsWith("iPhone")) {
      imageView.setImageResource(R.drawable.no);
    } else {
      imageView.setImageResource(R.drawable.ok);
    }

    return rowView;
  }
}

3.4. Updating the data model from the adapter

The row can also contain views which interact with the underlying data model via the adapter. For example, you can have a Checkbox in your row layout and if the Checkbox is selected, the underlying data is changed.

4. ListActivity and ListFragment

4.1. Default container for using ListView

Android provides specialized fragment and activity classes to simplify list handling.
The classes are the ListActivity class if you want to use lists in activities and the the ListFragment class if you want to use lists in fragments.
You do not have to assign a layout to these elements. If you do not define a layout, the activity or fragment contains a single ListView by default. ListActivity and ListFragment also allow you to override a onListItemClick() method for handling selection of list items.
Both classes allow you to set the adapter to the default ListView via the setListAdapter() method.
The following example code shows a simple ListFragment implementation.

package de.vogella.android.fragments;

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.app.ListFragment;

public class MyListFragment extends ListFragment {

  @Override
  public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);
    String[] values = new String[] { "Android", "iPhone", "WindowsMobile",
        "Blackberry", "WebOS", "Ubuntu", "Windows7", "Max OS X",
        "Linux", "OS/2" };
    ArrayAdapter<String> adapter = new ArrayAdapter<String>(getActivity(),
        android.R.layout.simple_list_item_1, values);
    setListAdapter(adapter);
  }

  @Override
  public void onListItemClick(ListView l, View v, int position, long id) {
    // TODO implement some logic 
  }
}

The next example code demonstrates the usage of a ListActivity.

package de.vogella.android.listactivity;

import android.app.ListActivity;
import android.os.Bundle;
import android.widget.ArrayAdapter;

public class MyListActivity extends ListActivity {
  public void onCreate(Bundle icicle) {
    super.onCreate(icicle);
    String[] values = new String[] { "Android", "iPhone", "WindowsMobile",
        "Blackberry", "WebOS", "Ubuntu", "Windows7", "Max OS X",
        "Linux", "OS/2" };
    ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
        android.R.layout.simple_list_item_1, values);
    setListAdapter(adapter);
  }
}

4.2. ListActivity and custom layout

You can use a custom layout with ListActivity or ListFragment. In this case the fragment or activity searches in the provided layout for a ListView with the pre-defined android:id attribute set to @android:id/list. This usage is demonstrated by the following code snippet.

<ListView
  android:id="@android:id/list"
  android:layout_width="match_parent"
  android:layout_height="wrap_content" >
</ListView>

Warning

If you do not use this ID or do not include a ListView into your layout, the application crashes once you try to display the activity or the fragment.

4.3. Placeholder for an empty list

You can also use a view with the @android:id/empty ID in your layout. The corresponding activity and fragment shows this view automatically if the ListView is empty and hides it otherwise. For example, you could display an error message in such a view.

5. Exercise: Using ListView and ListActivity

The following exercise demonstrates how to use a ListView in an ListActivity. You use the predefined ArrayAdapter class and an existing Android layout for the rows.
Create a new Android project called de.vogella.android.listactivity with the activity called MyListActivity.
Change MyListActivity class based on the the following code example. Note that the setContentView() method is not used.

package de.vogella.android.listactivity;

import android.app.ListActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;

public class MyListActivity extends ListActivity {
  public void onCreate(Bundle icicle) {
    super.onCreate(icicle);
    String[] values = new String[] { "Android", "iPhone", "WindowsMobile",
        "Blackberry", "WebOS", "Ubuntu", "Windows7", "Max OS X",
        "Linux", "OS/2" };
    ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
        android.R.layout.simple_list_item_1, values);
    setListAdapter(adapter);
  }

  @Override
  protected void onListItemClick(ListView l, View v, int position, long id) {
    String item = (String) getListAdapter().getItem(position);
    Toast.makeText(this, item + " selected", Toast.LENGTH_LONG).show();
  }
}

6. Exercise: ListActivity with own layout

In our example your will define your layout for the rows and use it in your adapter.
Create the rowlayout.xml layout file in the res/layout folder of the de.vogella.android.listactivity project.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content" >

    <ImageView
        android:id="@+id/icon"
        android:layout_width="22px"
        android:layout_height="22px"
        android:layout_marginLeft="4px"
        android:layout_marginRight="10px"
        android:layout_marginTop="4px"
        android:src="@drawable/ic_launcher" >
    </ImageView>

    <TextView
        android:id="@+id/label"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@+id/label"
        android:textSize="20px" >
    </TextView>

</LinearLayout>

Change your activity so that is using the new layout.

package de.vogella.android.listactivity;

import android.app.ListActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;

public class MyListActivity extends ListActivity {
  public void onCreate(Bundle icicle) {
    super.onCreate(icicle);
    String[] values = new String[] { "Android", "iPhone", "WindowsMobile",
        "Blackberry", "WebOS", "Ubuntu", "Windows7", "Max OS X",
        "Linux", "OS/2" };
    // use your custom layout
    ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
        R.layout.rowlayout, R.id.label, values);
    setListAdapter(adapter);
  }

  @Override
  protected void onListItemClick(ListView l, View v, int position, long id) {
    String item = (String) getListAdapter().getItem(position);
    Toast.makeText(this, item + " selected", Toast.LENGTH_LONG).show();
  }
}

7. Tutorial: Implementing your own adapter

The following uses two images "no.png" and "ok.png". I placed it in the "res/drawable-mdpi" folder. You must create your own icons. In case you do not find any icons just copy "icon.png" and use a drawing program to change it a little bit.
Create the class MySimpleArrayAdapter which will serve as our adapter.

package de.vogella.android.listactivity;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.TextView;

public class MySimpleArrayAdapter extends ArrayAdapter<String> {
  private final Context context;
  private final String[] values;

  public MySimpleArrayAdapter(Context context, String[] values) {
    super(context, R.layout.rowlayout, values);
    this.context = context;
    this.values = values;
  }

  @Override
  public View getView(int position, View convertView, ViewGroup parent) {
    LayoutInflater inflater = (LayoutInflater) context
        .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    View rowView = inflater.inflate(R.layout.rowlayout, parent, false);
    TextView textView = (TextView) rowView.findViewById(R.id.label);
    ImageView imageView = (ImageView) rowView.findViewById(R.id.icon);
    textView.setText(values[position]);
    // Change the icon for Windows and iPhone
    String s = values[position];
    if (s.startsWith("Windows7") || s.startsWith("iPhone")
        || s.startsWith("Solaris")) {
      imageView.setImageResource(R.drawable.no);
    } else {
      imageView.setImageResource(R.drawable.ok);
    }

    return rowView;
  }
}

To use this adapter, change the activity to the following.

package de.vogella.android.listactivity;

import android.app.ListActivity;
import android.os.Bundle;

public class MyListActivity extends ListActivity {
  public void onCreate(Bundle icicle) {
    super.onCreate(icicle);
    String[] values = new String[] { "Android", "iPhone", "WindowsMobile",
        "Blackberry", "WebOS", "Ubuntu", "Windows7", "Max OS X",
        "Linux", "OS/2" };
    MySimpleArrayAdapter adapter = new MySimpleArrayAdapter(this, values);
    setListAdapter(adapter);
  }

}

If you run this example you should get a list with different icons for the certain elements.

8. ListViews and performance

8.1. Motivation

Performance is especially important on Android as users expect fast reaction times. Compared to desktop computers an Android device is relatively slow from the hardware perspective.
This part describes how to reduce these operations to implement your custom list adapter efficiently. The default Android adapters like ArrayAdapter are already performance optimized.

8.2. Time consuming operations

Every view which get inflated from an XML layout file will result in a Java object. Inflating layouts and creating Java objects is expensive with regards to time and memory consumption.
In addition using the findViewById() method is relatively time consuming, even though it is not as bad as XML inflating.

8.3. Avoiding layout inflation and object creation

A ListView typically contains more data than the number of displayed rows. If the user scrolls the list, then rows and their associated views are being scrolled out of the visible area. The Java objects which represents the rows can be reused for newly visible rows.
If Android determines that a row is not visible anymore, it allows the getView() of the adapter method to reuse the associated view via the convertView parameter.
The adapter can assign new data to the views contained in the view hierarchy of the convertView. This avoids inflating an XML file and creating new Java objects.
In case Android cannot reuse a row, the Android system passes null to the convertView parameter. Therefore the adapter implementation needs to check for this.

8.4. View holder pattern

A ViewHolder implementation allows to avoid the findViewById() method in an adapter.
A ViewHolder class is typically a static inner class in your adapter which holds references to the relevant views. in your layout. This reference is assigned to the row view as a tag via the setTag() method.
If we receive a convertView object, we can get the instance of the ViewHolder via the getTag() method and assign the new attributes to the views via the ViewHolder reference.
While this sounds complex this is approximately 15 % faster then using the findViewById() method.

8.5. Example

The following code shows a performance optimized adapter implementation which reuses existing views and implements the holder pattern.

package de.vogella.android.listactivity;

import android.app.Activity;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.TextView;

public class MyPerformanceArrayAdapter extends ArrayAdapter<String> {
  private final Activity context;
  private final String[] names;

  static class ViewHolder {
    public TextView text;
    public ImageView image;
  }

  public MyPerformanceArrayAdapter(Activity context, String[] names) {
    super(context, R.layout.rowlayout, names);
    this.context = context;
    this.names = names;
  }

  @Override
  public View getView(int position, View convertView, ViewGroup parent) {
    View rowView = convertView;
    // reuse views
    if (rowView == null) {
      LayoutInflater inflater = context.getLayoutInflater();
      rowView = inflater.inflate(R.layout.rowlayout, null);
      // configure view holder
      ViewHolder viewHolder = new ViewHolder();
      viewHolder.text = (TextView) rowView.findViewById(R.id.TextView01);
      viewHolder.image = (ImageView) rowView
          .findViewById(R.id.ImageView01);
      rowView.setTag(viewHolder);
    }

    // fill data
    ViewHolder holder = (ViewHolder) rowView.getTag();
    String s = names[position];
    holder.text.setText(s);
    if (s.startsWith("Windows7") || s.startsWith("iPhone")
        || s.startsWith("Solaris")) {
      holder.image.setImageResource(R.drawable.no);
    } else {
      holder.image.setImageResource(R.drawable.ok);
    }

    return rowView;
  }
}

9. Storing the selection of a view

By default a ListView has no selection mode active. You can activate it via the setChoiceMode() method call. Pass ListView.CHOICE_MODE_MULTIPLE for multiple selections or ListView.CHOICE_MODE_SINGLE for single selections to this method.
To get the selected items of a ListView, use the getCheckedItemPosition() for a single selection method or listView.getCheckedItemPositions() for multiple selections. . If you have stable ID, you could also use the getCheckedItemIds() method to get the selected IDs.
Android already provides a default layout for this: the android.R.layout.simple_list_item_multiple_choice layout which contains a configured CheckedTextView view.
The following activities demonstrate how to use these selection modes. If you use these modes, the ListView stores the selected values. It is not persisted in your data model.

package com.vogella.android.listview.selection.multi;

import android.app.ListActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;

import com.vogella.android.listview.selection.R;

public class MainActivity extends ListActivity {

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    String[] values = new String[] { "a", "b", "c", "d", "e", "f", "g",
        "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s",
        "t", "u", "w", "x", "y", "z" };
    
    ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
        android.R.layout.simple_list_item_multiple_choice, values);
    setListAdapter(adapter);
    getListView().setChoiceMode(ListView.CHOICE_MODE_MULTIPLE);
  }

  @Override
  public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
  }

  @Override
  public boolean onOptionsItemSelected(MenuItem item) {
    Toast.makeText(this,
        String.valueOf(getListView().getCheckedItemCount()),
        Toast.LENGTH_LONG).show();
    return true;
  }
}

package com.vogella.android.listview.selection.single;

import android.app.ListActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;


public class MainActivity extends ListActivity {

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    String[] values = new String[] { "a", "b", "c", "d", "e", "f", "g",
        "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s",
        "t", "u", "w", "x", "y", "z" };
    
    ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
        android.R.layout.simple_list_item_single_choice, values);
    setListAdapter(adapter);
    getListView().setChoiceMode(ListView.CHOICE_MODE_SINGLE);
  }

  @Override
  public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
  }

  @Override
  public boolean onOptionsItemSelected(MenuItem item) {
    Toast.makeText(this,
        String.valueOf(getListView().getCheckedItemCount()),
        Toast.LENGTH_LONG).show();
    return true;
  }
}

10. Contextual action mode for ListViews

The following assumes that you already familiar with the concept of the ActionBar and contextual action mode in general. This part will explain how to use contextual action mode for a ListView selection.
To assign a contextual action mode to a long click on an individual item, use the method setOnItemLongClickListener() on ListView. This methods includes information about the selected item. In this method you can start the ActionMode.
The following examples demonstrate that. It assumes that you have a menu XML file defined called rowselection.xml and that this menu contains one entry with the @+id/menuitem1_show ID.

package de.vogella.android.listactivity;

import android.app.ListActivity;
import android.os.Bundle;
import android.view.ActionMode;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemLongClickListener;
import android.widget.Toast;

public class MyListActivityActionbar extends ListActivity 
    implements ActionMode.Callback {

  protected Object mActionMode;
  public int selectedItem = -1;

  @Override
  public void onCreate(Bundle icicle) {
    super.onCreate(icicle);
    String[] values = new String[] { "Android", 
        "iPhone", "WindowsMobile", 
        "Blackberry", "WebOS", "Ubuntu",
        "Windows7", "Max OS X", "Linux", "OS/2", 
        "Ubuntu", "Windows7", "Max OS X", 
        "Linux", "OS/2", "Ubuntu",
        "Windows7", "Max OS X", 
        "Linux", "OS/2" };

    MySimpleArrayAdapter adapter = new MySimpleArrayAdapter(this, values);
    setListAdapter(adapter);

    getListView().setOnItemLongClickListener(new OnItemLongClickListener() {

      @Override
      public boolean onItemLongClick(AdapterView<?> parent, View view, int position, long id) {

        if (mActionMode != null) {
          return false;
        }
        selectedItem = position;

        // Start the CAB using the ActionMode.Callback defined above
        mActionMode = MyListActivityActionbar.this.startActionMode(MyListActivityActionbar.this);
        view.setSelected(true);
        return true;
      }
    });
  }

  private void show() {
    Toast.makeText(MyListActivityActionbar.this, String.valueOf(selectedItem), Toast.LENGTH_LONG).show();
  }

  // Called when the action mode is created; startActionMode() was called
  @Override
  public boolean onCreateActionMode(ActionMode mode, Menu menu) {
    // Inflate a menu resource providing context menu items
    MenuInflater inflater = mode.getMenuInflater();
    // Assumes that you have "contexual.xml" menu resources
    inflater.inflate(R.menu.rowselection, menu);
    return true;
  }

  // Called each time the action mode is shown. Always called after
  // onCreateActionMode, but
  // may be called multiple times if the mode is invalidated.
  @Override
  public boolean onPrepareActionMode(ActionMode mode, Menu menu) {
    return false; // Return false if nothing is done
  }

  // Called when the user selects a contextual menu item
  @Override
  public boolean onActionItemClicked(ActionMode mode, MenuItem item) {
    switch (item.getItemId()) {
    case R.id.menuitem1_show:
      show();
      // Action picked, so close the CAB
      mode.finish();
      return true;
    default:
      return false;
    }
  }

  // Called when the user exits the action mode
  @Override
  public void onDestroyActionMode(ActionMode mode) {
    mActionMode = null;
    selectedItem = -1;
  }

}

If you start your application and long press on an item in the list, you get your contextual action bar.

11. Implementing undo for an action

11.1. When should you offer an undo action?

It is good practice to allow the user to undo critical actions. Such a critical action is, for example, the deletion of list items.
A proven pattern to handle this undo option is to offer a selection at the end of the screen. This selection vanishes after a predefined time or once the user continues to interact with the application.
For example, the Gmail application implements such a behavior.

11.2. Example

The following description contains an example for implementing an undo action. It uses an animation to phase out the undo button automatically out after a while.
For this example create a new project called com.vogella.android.userinterface.undo based on the BlankTemplate template.
Create the following layout for your activity. It uses a FrameLayout to show two different parts of the user interface. The button bar is initially hidden. The button uses a drawable. Either add such a drawable to your project or remove the reference.

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".MainActivity" >

        <ListView
            android:id="@+id/listview"
            android:layout_width="match_parent"
            android:layout_height="match_parent" >
        </ListView>
    </RelativeLayout>

    <LinearLayout
        android:id="@+id/undobar"
        android:visibility="gone"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom|center_horizontal"
        android:layout_margin="20dp"
        android:alpha="100"
        android:background="#808080"
        android:dividerPadding="11dp"
        android:padding="4dp" >

        <TextView
            android:id="@+id/undobar_message"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Deleted"
            android:textAppearance="?android:attr/textAppearanceMedium"
            android:textColor="#fff" />

        <Button
            android:id="@+id/undobar_button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginLeft="30dp"
            android:onClick="onClick"
            android:background="#808080"
            android:drawableLeft="@drawable/ic_undobar_undo"
            android:text="Undo"
            android:textAppearance="?android:attr/textAppearanceMedium"
            android:textColor="#fff" />
    </LinearLayout>

</FrameLayout>

Change your activity so that it is similar to the following code. The Android project wizard in Eclipse already generated an ActionBar entry. This entry is used in the following code. If in doubt, create your own ActionBar entry.

package com.vogella.android.userinterface.undo;

import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;

import com.vogella.android.actionbar.undo.R;

public class MainActivity extends Activity {

  private View viewContainer;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    ListView l = (ListView) findViewById(R.id.listview);
    String[] values = new String[] { "Ubuntu", "Android", "iPhone",
        "Windows", "Ubuntu", "Android", "iPhone", "Windows" };
    ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
        android.R.layout.simple_list_item_1, values);
    viewContainer = findViewById(R.id.undobar);
    l.setAdapter(adapter);
  }

  @Override
  public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.activity_main, menu);
    return true;
  }

  @Override
  public boolean onOptionsItemSelected(MenuItem item) {
    showUndo(viewContainer);
    return true;
  }

  public void onClick(View view) {
    Toast.makeText(this, "Deletion undone", Toast.LENGTH_LONG).show();
    viewContainer.setVisibility(View.GONE);
  }

  public static void showUndo(final View viewContainer) {
    viewContainer.setVisibility(View.VISIBLE);
    viewContainer.setAlpha(1);
    viewContainer.animate().alpha(0.4f).setDuration(5000)
        .withEndAction(new Runnable() {

          @Override
          public void run() {
            viewContainer.setVisibility(View.GONE);
          }
        });

  }
}

If you select the entry in the ActionBar, the button bar becomes visible for 5 seconds.

12. Performance Optimization

The following will implement a performance optimized version of the adapter from the previous example.
Create the following MyPerformanceArrayAdapter class.

package de.vogella.android.listactivity;

import android.app.Activity;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.TextView;

public class MyPerformanceArrayAdapter extends ArrayAdapter<String> {
  private final Activity context;
  private final String[] names;

  static class ViewHolder {
    public TextView text;
    public ImageView image;
  }

  public MyPerformanceArrayAdapter(Activity context, String[] names) {
    super(context, R.layout.rowlayout, names);
    this.context = context;
    this.names = names;
  }

  @Override
  public View getView(int position, View convertView, ViewGroup parent) {
    View rowView = convertView;
    // reuse views
    if (rowView == null) {
      LayoutInflater inflater = context.getLayoutInflater();
      rowView = inflater.inflate(R.layout.rowlayout, null);
      // configure view holder
      ViewHolder viewHolder = new ViewHolder();
      viewHolder.text = (TextView) rowView.findViewById(R.id.TextView01);
      viewHolder.image = (ImageView) rowView
          .findViewById(R.id.ImageView01);
      rowView.setTag(viewHolder);
    }

    // fill data
    ViewHolder holder = (ViewHolder) rowView.getTag();
    String s = names[position];
    holder.text.setText(s);
    if (s.startsWith("Windows7") || s.startsWith("iPhone")
        || s.startsWith("Solaris")) {
      holder.image.setImageResource(R.drawable.no);
    } else {
      holder.image.setImageResource(R.drawable.ok);
    }

    return rowView;
  }
}

Use your new adapter in your activity. If you run the application it should look the same but it will be much faster, especially for large datasets.

package de.vogella.android.listactivity;

import android.app.ListActivity;
import android.os.Bundle;

public class MyListActivity extends ListActivity {
  public void onCreate(Bundle icicle) {
    super.onCreate(icicle);
    String[] values = new String[] { "Android", "iPhone", "WindowsMobile",
        "Blackberry", "WebOS", "Ubuntu", "Windows7", "Max OS X",
        "Linux", "OS/2" };
    setListAdapter(new MyPerformanceArrayAdapter(this, values));
  }

}

13. Tutorial: How to display two items in a ListView

You can use the SimpleAdapter class to show the data of two elements. This class expects a Array of Strings (from data) in which the fields of the input data are defined. It also requires a Array of ints which defines the IDs of the widgets in the layout for the row to which these fields are mapped.
The actual data is then a list of Maps. The Map defines for each field in the from data a value.
The following shows an example which reuses an predefined layout from Android for the row.

package de.vogella.android.listactivity;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;

import android.app.ListActivity;
import android.os.Bundle;
import android.widget.SimpleAdapter;

public class MyTwoListItemsActivity extends ListActivity {
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    ArrayList<Map<String, String>> list = buildData();
    String[] from = { "name", "purpose" };
    int[] to = { android.R.id.text1, android.R.id.text2 };

    SimpleAdapter adapter = new SimpleAdapter(this, list,
        android.R.layout.simple_list_item_2, from, to);
    setListAdapter(adapter);
  }

  private ArrayList<Map<String, String>> buildData() {
    ArrayList<Map<String, String>> list = new ArrayList<Map<String, String>>();
    list.add(putData("Android", "Mobile"));
    list.add(putData("Windows7", "Windows7"));
    list.add(putData("iPhone", "iPhone"));
    return list;
  }

  private HashMap<String, String> putData(String name, String purpose) {
    HashMap<String, String> item = new HashMap<String, String>();
    item.put("name", name);
    item.put("purpose", purpose);
    return item;
  }
  
}

14. Selecting multiple items in the ListView

14.1. Interaction between the model and Listview

Frequently you need to select items in your ListView. As the row of the ListView are getting recycled you cannot store the selection on the View level.

Selection is just one possible example but you can imange other interaction between your row and model.
To persist the selection you have to update your data model with the selected state.
To update the data model in your ListView you define your own Adapter class. In this adapter class you attach a listener to the View which is responsible for selecting the model element. If selected you update the state in the model which you can add as a tag to the View to have access to it.
The following example demonstrates how to use standard Java object and how to interact from the Views with the model.

14.2. Tutorial: Domain Model and Rows interaction

Continue to use the de.vogella.android.listactivity project.
Create the following Model which hold the name and the information if this element is currently selected.

package de.vogella.android.listactivity;

public class Model {

  private String name;
  private boolean selected;

  public Model(String name) {
    this.name = name;
    selected = false;
  }

  public String getName() {
    return name;
  }

  public void setName(String name) {
    this.name = name;
  }

  public boolean isSelected() {
    return selected;
  }

  public void setSelected(boolean selected) {
    this.selected = selected;
  }

}

Create the following new layout file called rowbuttonlayout.xml.

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content" >

    <TextView
        android:id="@+id/label"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@+id/label"
        android:textSize="30px" >
    </TextView>

    <CheckBox
        android:id="@+id/check"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentRight="true"
        android:layout_marginLeft="4px"
        android:layout_marginRight="10px" >
    </CheckBox>

</RelativeLayout>

Create the following Adapter. This adapter adds a listener on the Checkbox view . If the checkbox is selected the underlying data of the model is changed. Checkbox gets the corresponding model element assigned via the getTag() method.

package de.vogella.android.listactivity;

import java.util.List;

import android.app.Activity;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.CheckBox;
import android.widget.CompoundButton;
import android.widget.TextView;

public class InteractiveArrayAdapter extends ArrayAdapter<Model> {

  private final List<Model> list;
  private final Activity context;

  public InteractiveArrayAdapter(Activity context, List<Model> list) {
    super(context, R.layout.rowbuttonlayout, list);
    this.context = context;
    this.list = list;
  }

  static class ViewHolder {
    protected TextView text;
    protected CheckBox checkbox;
  }

  @Override
  public View getView(int position, View convertView, ViewGroup parent) {
    View view = null;
    if (convertView == null) {
      LayoutInflater inflator = context.getLayoutInflater();
      view = inflator.inflate(R.layout.rowbuttonlayout, null);
      final ViewHolder viewHolder = new ViewHolder();
      viewHolder.text = (TextView) view.findViewById(R.id.label);
      viewHolder.checkbox = (CheckBox) view.findViewById(R.id.check);
      viewHolder.checkbox
          .setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {

            @Override
            public void onCheckedChanged(CompoundButton buttonView,
                boolean isChecked) {
              Model element = (Model) viewHolder.checkbox
                  .getTag();
              element.setSelected(buttonView.isChecked());

            }
          });
      view.setTag(viewHolder);
      viewHolder.checkbox.setTag(list.get(position));
    } else {
      view = convertView;
      ((ViewHolder) view.getTag()).checkbox.setTag(list.get(position));
    }
    ViewHolder holder = (ViewHolder) view.getTag();
    holder.text.setText(list.get(position).getName());
    holder.checkbox.setChecked(list.get(position).isSelected());
    return view;
  }
}

Finally change your activity to the following.

package de.vogella.android.listactivity;

import java.util.ArrayList;
import java.util.List;

import android.app.ListActivity;
import android.os.Bundle;
import android.widget.ArrayAdapter;

public class MyList extends ListActivity {

  
/** Called when the activity is first created. */
public void onCreate(Bundle icicle) {
    super.onCreate(icicle);
    // create an array of Strings, that will be put to our ListActivity
    ArrayAdapter<Model> adapter = new InteractiveArrayAdapter(this,
        getModel());
    setListAdapter(adapter);
  }

  private List<Model> getModel() {
    List<Model> list = new ArrayList<Model>();
    list.add(get("Linux"));
    list.add(get("Windows7"));
    list.add(get("Suse"));
    list.add(get("Eclipse"));
    list.add(get("Ubuntu"));
    list.add(get("Solaris"));
    list.add(get("Android"));
    list.add(get("iPhone"));
    // Initially select one of the items
    list.get(1).setSelected(true);
    return list;
  }

  private Model get(String s) {
    return new Model(s);
  }

}

If you start your app you should be able to flag items. These changes will be reflected in your model.

15. Implementing an expandable ListView

15.1. ExpandableListView

The ExpandableListView is similar to ListView but allow you to define groups and details for this group. ExpandableListView expects and adapter of type BaseExpandableListAdapter.
In this case you have to define two layouts, one for the group and another one for the details row.

15.2. ExpandableListView example

In the following example you create an expandable listview similar to the following screenshot.

Create a project called com.vogella.android.listview.expandable with the activity called MainActivity.
Create or adjust the following layout files. First layout/activity_main.xml.

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/LinearLayout1"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

    <ExpandableListView
        android:id="@+id/listView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" >
    </ExpandableListView>

</LinearLayout>

Afterwards create layout/listrow_group.xml.

<CheckedTextView xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/textView1"
    android:layout_width="wrap_content"
    android:layout_height="?android:attr/listPreferredItemHeight"
    android:layout_marginLeft="8dp"
    android:drawableRight="@drawable/ic_launcher"
    android:gravity="left"
    android:paddingLeft="32dp"
    android:paddingTop="8dp"
    android:text="Test"
    android:textSize="14sp"
    android:textAlignment="textEnd"
    android:textStyle="bold" />

The last required layout is layout/listrow_details.xml.

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="40dp"
    android:clickable="true"
    android:orientation="vertical"
    android:paddingLeft="40dp"
    tools:context=".MainActivity" >

    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:drawableLeft="@drawable/ic_launcher"
        android:drawablePadding="5dp"
        android:gravity="center_vertical"
        android:text="@string/hello_world"
        android:textSize="14sp"
        android:textStyle="bold" >
    </TextView>

    <View
        android:layout_width="match_parent"
        android:layout_height="1dp"
        android:background="@android:color/black" />

</LinearLayout>

Create the following class which hold your domain model for the ExpandableListView.

package com.vogella.android.listview.expandable;

import java.util.ArrayList;
import java.util.List;

public class Group {

  public String string;
  public final List<String> children = new ArrayList<String>();

  public Group(String string) {
    this.string = string;
  }

}

Finally create the adapter as described by the following listing and change the activity to the code provided below.

package com.vogella.android.listview.expandable;

import android.app.Activity;
import android.util.SparseArray;
import android.view.LayoutInflater;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.BaseExpandableListAdapter;
import android.widget.CheckedTextView;
import android.widget.TextView;
import android.widget.Toast;

public class MyExpandableListAdapter extends BaseExpandableListAdapter {

  private final SparseArray<Group> groups;
  public LayoutInflater inflater;
  public Activity activity;

  public MyExpandableListAdapter(Activity act, SparseArray<Group> groups) {
    activity = act;
    this.groups = groups;
    inflater = act.getLayoutInflater();
  }

  @Override
  public Object getChild(int groupPosition, int childPosition) {
    return groups.get(groupPosition).children.get(childPosition);
  }

  @Override
  public long getChildId(int groupPosition, int childPosition) {
    return 0;
  }

  @Override
  public View getChildView(int groupPosition, final int childPosition,
      boolean isLastChild, View convertView, ViewGroup parent) {
    final String children = (String) getChild(groupPosition, childPosition);
    TextView text = null;
    if (convertView == null) {
      convertView = inflater.inflate(R.layout.listrow_details, null);
    }
    text = (TextView) convertView.findViewById(R.id.textView1);
    text.setText(children);
    convertView.setOnClickListener(new OnClickListener() {
      @Override
      public void onClick(View v) {
        Toast.makeText(activity, children,
            Toast.LENGTH_SHORT).show();
      }
    });
    return convertView;
  }

  @Override
  public int getChildrenCount(int groupPosition) {
    return groups.get(groupPosition).children.size();
  }

  @Override
  public Object getGroup(int groupPosition) {
    return groups.get(groupPosition);
  }

  @Override
  public int getGroupCount() {
    return groups.size();
  }

  @Override
  public void onGroupCollapsed(int groupPosition) {
    super.onGroupCollapsed(groupPosition);
  }

  @Override
  public void onGroupExpanded(int groupPosition) {
    super.onGroupExpanded(groupPosition);
  }

  @Override
  public long getGroupId(int groupPosition) {
    return 0;
  }

  @Override
  public View getGroupView(int groupPosition, boolean isExpanded,
      View convertView, ViewGroup parent) {
    if (convertView == null) {
      convertView = inflater.inflate(R.layout.listrow_group, null);
    }
    Group group = (Group) getGroup(groupPosition);
    ((CheckedTextView) convertView).setText(group.string);
    ((CheckedTextView) convertView).setChecked(isExpanded);
    return convertView;
  }

  @Override
  public boolean hasStableIds() {
    return false;
  }

  @Override
  public boolean isChildSelectable(int groupPosition, int childPosition) {
    return false;
  }
}

package com.vogella.android.listview.expandable;

import java.util.ArrayList;

import android.app.Activity;
import android.os.Bundle;
import android.util.SparseArray;
import android.view.Menu;
import android.widget.ExpandableListView;

public class MainActivity extends Activity {
  // more efficient than HashMap for mapping integers to objects
  SparseArray<Group> groups = new SparseArray<Group>();

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    createData();
    ExpandableListView listView = (ExpandableListView) findViewById(R.id.listView);
    MyExpandableListAdapter adapter = new MyExpandableListAdapter(this,
        groups);
    listView.setAdapter(adapter);
  }

  public void createData() {
    for (int j = 0; j < 5; j++) {
      Group group = new Group("Test " + j);
      for (int i = 0; i < 5; i++) {
        group.children.add("Sub Item" + i);
      }
      groups.append(j, group);
    }
  }

}

16. Tutorial: Miscellaneous

16.1. Adding a longclick listener to the list items

You can also add a LongItemClickListener to the View. For this receive the ListView via the getListVIew() method and set the LongItemClickListener via the setOnItemLongClickListener() method.

package de.vogella.android.listactivity;

import android.app.ListActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemLongClickListener;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;

public class MyList extends ListActivity {

  
/** Called when the activity is first created. */
public void onCreate(Bundle icicle) {
    super.onCreate(icicle);
    // create an array of Strings, that will be put to our ListActivity
    String[] names = new String[] { "Linux", "Windows7", "Eclipse", "Suse",
        "Ubuntu", "Solaris", "Android", "iPhone" };
    ArrayAdapter<String> adapter = new MyPerformanceArrayAdapter(this, names);
    setListAdapter(adapter);
    ListView list = getListView();
    list.setOnItemLongClickListener(new OnItemLongClickListener() {

      @Override
      public boolean onItemLongClick(AdapterView<?> parent, View view,
          int position, long id) {
        Toast.makeText(MyList.this,
            "Item in position " + position + " clicked",
            Toast.LENGTH_LONG).show();
        // Return true to consume the click event. In this case the
        // onListItemClick listener is not called anymore.
        return true;
      }
    });
  }

  @Override
  protected void onListItemClick(ListView l, View v, int position, long id) {
    super.onListItemClick(l, v, position, id);
    // Get the item that was clicked
    Object o = this.getListAdapter().getItem(position);
    String keyword = o.toString();
    Toast.makeText(this, "You selected: " + keyword, Toast.LENGTH_SHORT)
        .show();

  }

}

16.2. Header and Footer

You can of course put arbitrary Views elements around your ListView. For example you can define a layout with two TextViews and a ListView between them. In this case the two TextViews will always be visible above the List (header) and the other will be visible below the ListView. If you want to display a list header or list footer only at the see the beginning or end of the list you can use the addHeaderView() method or addFooterView() method on the ListView class.

package de.vogella.android.listactivity;

import android.app.ListActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.ListView;

public class MyList extends ListActivity {

  
/** Called when the activity is first created. */
public void onCreate(Bundle icicle) {
    super.onCreate(icicle);
    // create an array of Strings, that will be put to our ListActivity
    String[] names = new String[] { "Linux", "Windows7", "Eclipse", "Suse",
        "Ubuntu", "Solaris", "Android", "iPhone", "Linux", "Windows7",
        "Eclipse", "Suse", "Ubuntu", "Solaris", "Android", "iPhone" };
    View header = getLayoutInflater().inflate(R.layout.header, null);
    View footer = getLayoutInflater().inflate(R.layout.footer, null);
    ListView listView = getListView();
    listView.addHeaderView(header);
    listView.addFooterView(footer);
    setListAdapter(new ArrayAdapter<String>(this,
        android.R.layout.simple_list_item_single_choice,
        android.R.id.text1, names));

  }
}

17. SimpleCursorAdapter

In case you work with a content provider or directly with the database you can use the SimpleCursorAdapter to define the data for your ListView. The following will demonstrates how to access the Contacts ContentProvider.
Create a new Android project called "de.vogella.android.listactivity.cursor" with the activity called MyListActivity. Change MyListActivity to the following.

package de.vogella.android.listactivity.cursor;

import android.app.ListActivity;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.provider.ContactsContract;
import android.widget.ListAdapter;
import android.widget.SimpleCursorAdapter;

public class MyListActivity extends ListActivity {
  
/** Called when the activity is first created. */
@Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    Cursor mCursor = getContacts();
    startManagingCursor(mCursor);
    // now create a new list adapter bound to the cursor.
    // SimpleListAdapter is designed for binding to a Cursor.
    ListAdapter adapter = new SimpleCursorAdapter(this, // Context.
        android.R.layout.two_line_list_item, // Specify the row template
                            // to use (here, two
                            // columns bound to the
                            // two retrieved cursor
                            // rows).
        mCursor, // Pass in the cursor to bind to.
        // Array of cursor columns to bind to.
        new String[] { ContactsContract.Contacts._ID,
            ContactsContract.Contacts.DISPLAY_NAME },
        // Parallel array of which template objects to bind to those
        // columns.
        new int[] { android.R.id.text1, android.R.id.text2 });

    // Bind to our new adapter.
    setListAdapter(adapter);
  }

  private Cursor getContacts() {
    // Run query
    Uri uri = ContactsContract.Contacts.CONTENT_URI;
    String[] projection = new String[] { ContactsContract.Contacts._ID,
        ContactsContract.Contacts.DISPLAY_NAME };
    String selection = ContactsContract.Contacts.IN_VISIBLE_GROUP + " = '"
        + ("1") + "'";
    String[] selectionArgs = null;
    String sortOrder = ContactsContract.Contacts.DISPLAY_NAME
        + " COLLATE LOCALIZED ASC";

    return managedQuery(uri, projection, selection, selectionArgs,
        sortOrder);
  }

}

Make sure you give your application the permission to read the contacts. (Uses Permissions "android.permission.READ_CONTACTS" in AndroidManifest.xml)

AngularJS - REST Services

2015-06-21T20:32:00.001+05:30

Dependencies

The RESTful functionality is provided by Angular in the ngResource module, which is distributed separately from the core Angular framework.

We are using Bower to install client side dependencies. This step updates the bower.json configuration file to include the new dependency:

{
  "name": "angular-seed",
  "description": "A starter project for AngularJS",
  "version": "0.0.0",
  "homepage": "https://github.com/angular/angular-seed",
  "license": "MIT",
  "private": true,
  "dependencies": {
    "angular": "~1.3.0",
    "angular-mocks": "~1.3.0",
    "bootstrap": "~3.1.1",
    "angular-route": "~1.3.0",
    "angular-resource": "~1.3.0"
  }
}

The new dependency "angular-resource": "~1.3.0" tells bower to install a version of the angular-resource component that is compatible with version 1.3.x. We must ask bower to download and install this dependency. We can do this by running:

npm install

Warning: If a new version of Angular has been released since you last ran npm install, then you may have a problem with the bower install due to a conflict between the versions of angular.js that need to be installed. If you get this then simply delete your app/bower_components folder before running npm install.

Note: If you have bower installed globally then you can run bower install but for this project we have preconfigured npm install to run bower for us.

Template

Our custom resource service will be defined in app/js/services.js so we need to include this file in our layout template. Additionally, we also need to load the angular-resource.js file, which contains the ngResource module:

app/index.html.

...
  <script src="bower_components/angular-resource/angular-resource.js"></script>
  <script src="js/services.js"></script>
...

Service

We create our own service to provide access to the phone data on the server:

app/js/services.js.

var phonecatServices = angular.module('phonecatServices', ['ngResource']);

phonecatServices.factory('Phone', ['$resource',
  function($resource){
    return $resource('phones/:phoneId.json', {}, {
      query: {method:'GET', params:{phoneId:'phones'}, isArray:true}
    });
  }]);

We used the module API to register a custom service using a factory function. We passed in the name of the service - 'Phone' - and the factory function. The factory function is similar to a controller's constructor in that both can declare dependencies to be injected via function arguments. The Phone service declared a dependency on the $resource service.

The $resource service makes it easy to create a RESTful client with just a few lines of code. This client can then be used in our application, instead of the lower-level $http service.

app/js/app.js.

...
angular.module('phonecatApp', ['ngRoute', 'phonecatControllers','phonecatFilters', 'phonecatServices']).
...

We need to add the 'phonecatServices' module dependency to 'phonecatApp' module's requires array.

Controller

We simplified our sub-controllers (PhoneListCtrl and PhoneDetailCtrl) by factoring out the lower-level $http service, replacing it with a new service called Phone. Angular's $resource service is easier to use than $http for interacting with data sources exposed as RESTful resources. It is also easier now to understand what the code in our controllers is doing.

app/js/controllers.js.

var phonecatControllers = angular.module('phonecatControllers', []);

...

phonecatControllers.controller('PhoneListCtrl', ['$scope', 'Phone', function($scope, Phone) {
  $scope.phones = Phone.query();
  $scope.orderProp = 'age';
}]);

phonecatControllers.controller('PhoneDetailCtrl', ['$scope', '$routeParams', 'Phone', function($scope, $routeParams, Phone) {
  $scope.phone = Phone.get({phoneId: $routeParams.phoneId}, function(phone) {
    $scope.mainImageUrl = phone.images[0];
  });

  $scope.setImage = function(imageUrl) {
    $scope.mainImageUrl = imageUrl;
  }
}]);

Notice how in PhoneListCtrl we replaced:

$http.get('phones/phones.json').success(function(data) {
  $scope.phones = data;
});

with:

$scope.phones = Phone.query();

This is a simple statement that we want to query for all phones.

An important thing to notice in the code above is that we don't pass any callback functions when invoking methods of our Phone service. Although it looks as if the result were returned synchronously, that is not the case at all. What is returned synchronously is a "future" — an object, which will be filled with data when the XHR response returns. Because of the data-binding in Angular, we can use this future and bind it to our template. Then, when the data arrives, the view will automatically update.

Sometimes, relying on the future object and data-binding alone is not sufficient to do everything we require, so in these cases, we can add a callback to process the server response. The PhoneDetailCtrl controller illustrates this by setting the mainImageUrl in a callback.

Test

Because we're now using the ngResource module, it's necessary to update the Karma config file with angular-resource so the new tests will pass.

test/karma.conf.js:

files : [
  'app/bower_components/angular/angular.js',
  'app/bower_components/angular-route/angular-route.js',
  'app/bower_components/angular-resource/angular-resource.js',
  'app/bower_components/angular-mocks/angular-mocks.js',
  'app/js/**/*.js',
  'test/unit/**/*.js'
],

We have modified our unit tests to verify that our new service is issuing HTTP requests and processing them as expected. The tests also check that our controllers are interacting with the service correctly.

The $resource service augments the response object with methods for updating and deleting the resource. If we were to use the standard toEqual matcher, our tests would fail because the test values would not match the responses exactly. To solve the problem, we use a newly-defined toEqualData Jasmine matcher. When the toEqualData matcher compares two objects, it takes only object properties into account and ignores methods.

test/unit/controllersSpec.js:

describe('PhoneCat controllers', function() {

  beforeEach(function(){
    this.addMatchers({
      toEqualData: function(expected) {
        return angular.equals(this.actual, expected);
      }
    });
  });

  beforeEach(module('phonecatApp'));
  beforeEach(module('phonecatServices'));


  describe('PhoneListCtrl', function(){
    var scope, ctrl, $httpBackend;

    beforeEach(inject(function(_$httpBackend_, $rootScope, $controller) {
      $httpBackend = _$httpBackend_;
      $httpBackend.expectGET('phones/phones.json').
          respond([{name: 'Nexus S'}, {name: 'Motorola DROID'}]);

      scope = $rootScope.$new();
      ctrl = $controller('PhoneListCtrl', {$scope: scope});
    }));


    it('should create "phones" model with 2 phones fetched from xhr', function() {
      expect(scope.phones).toEqualData([]);
      $httpBackend.flush();

      expect(scope.phones).toEqualData(
          [{name: 'Nexus S'}, {name: 'Motorola DROID'}]);
    });


    it('should set the default value of orderProp model', function() {
      expect(scope.orderProp).toBe('age');
    });
  });


  describe('PhoneDetailCtrl', function(){
    var scope, $httpBackend, ctrl,
        xyzPhoneData = function() {
          return {
            name: 'phone xyz',
            images: ['image/url1.png', 'image/url2.png']
          }
        };


    beforeEach(inject(function(_$httpBackend_, $rootScope, $routeParams, $controller) {
      $httpBackend = _$httpBackend_;
      $httpBackend.expectGET('phones/xyz.json').respond(xyzPhoneData());

      $routeParams.phoneId = 'xyz';
      scope = $rootScope.$new();
      ctrl = $controller('PhoneDetailCtrl', {$scope: scope});
    }));


    it('should fetch phone detail', function() {
      expect(scope.phone).toEqualData({});
      $httpBackend.flush();

      expect(scope.phone).toEqualData(xyzPhoneData());
    });
  });
});

You should now see the following output in the Karma tab:

Chrome 22.0: Executed 5 of 5 SUCCESS (0.038 secs / 0.01 secs)

Securing REST Services with Spring Security and OAuth2

2015-06-18T22:37:00.001+05:30

This post will walk through setting up an OAuth2 provider service for protecting access to REST resources. The code is available in github. You can fork the code and start writing services that will be protected by OAuth access. This is a separate module but builds on services covered in a previous series that includes:

* User Registration and Login
* Email Verification
* Lost Password
* JSR 303 Validation

It would be useful but not required to be familiar with some of the technologies covered such as:

* OAuth2 Protocol
* Spring Security
* Spring Integration
* Spring Data
* Jersey/JAX-RS
* Gradle / Groovy
* MongoDB

Resource Owner Password Flow

Subsequent posts will deal with the other types of authorization flow, such as using third party providers (Facebook, Google, etc). The intent of this post is a walk through of the Resource Owner Password flow. This is a typical use case if you are the system of record for user credentials and trust client applications. It is simply the exchange of the user's username and password for an access token. This token can then be used on subsequent requests to authorize access to resources. It is also important to support token expiration and by extension token refresh.

Let's test out the code and then I'll walk through the application and explain how it is built

Building the project

Check out the source code

> git clone git@github.com:iainporter/oauth2-provider.git

> cd oauth2-provider

> ./gradlew clean build integrationTest

Running the Web Application

The application uses MongoDB as the persistence store. Before running the application ensure that mongod is running on port 27017. If you don't have mongo installed get it here

Once mongoDB is installed and running fire up the web application using the following command

> ./gradlew tomcatRun

To try it out you can open a browser window and navigate to http://localhost:8080/oauth2-provider/index.html

Testing with Curl

To create a user:

> curl -v -X POST \
   -H "Content-Type: application/json" \
   -H "Authorization: Basic MzUzYjMwMmM0NDU3NGY1NjUwNDU2ODdlNTM0ZTdkNmE6Mjg2OTI0Njk3ZTYxNWE2NzJhNjQ2YTQ5MzU0NTY0NmM=" \
   -d '{"user":{"emailAddress":"user@example.com"}, "password":"password"}' \
   'http://localhost:8080/oauth2-provider/v1.0/users'

The result:

{"apiUser":
   {"emailAddress":"user@example.com",
   "firstName":null,
   "lastName":null,
   "age":null,
   "id":"8a34d009-3558-4c8c-a8da-1ad2b2a393c7",
   "name":"user@example.com"},
   "oauth2AccessToken":
   {"access_token":"7e0e4708-7837-4a7e-9f87-81c6429b02ac",
   "token_type":"bearer",
   "refresh_token":"d0f248ab-e30f-4a85-860c-bd1e388a39b5",
   "expires_in":5183999,
   "scope":"read write"
   }
}

Requesting an access token:

> curl -v -X POST \
   -H "Content-Type: application/json" \
   -H "Authorization: Basic MzUzYjMwMmM0NDU3NGY1NjUwNDU2ODdlNTM0ZTdkNmE6Mjg2OTI0Njk3ZTYxNWE2NzJhNjQ2YTQ5MzU0NTY0NmM=" \
   'http://localhost:8080/oauth2-provider/oauth/token?grant_type=password&username=user@example.com&password=password'

The result:

{
  "access_token":"a838780e-35ef-4bd5-92c0-07a45aa74948",
  "token_type":"bearer",
  "refresh_token":"ab06022f-247c-450a-a11e-2ffab116e3dc",
  "expires_in":5183999
}

Refreshing a token:

> curl -v -X POST \
   -H "Content-Type: application/json" \
   -H "Authorization: Basic MzUzYjMwMmM0NDU3NGY1NjUwNDU2ODdlNTM0ZTdkNmE6Mjg2OTI0Njk3ZTYxNWE2NzJhNjQ2YTQ5MzU0NTY0NmM=" \
   'http://localhost:8080/oauth2-provider/oauth/token?grant_type=refresh_token&refresh_token=ab06022f-247c-450a-a11e-2ffab116e3dc'

The result:

{
   "access_token":"4835cd11-8bb7-4b76-b857-55c6e7f36fc4",
   "token_type":"bearer",
   "refresh_token":"ab06022f-247c-450a-a11e-2ffab116e3dc",
   "expires_in":5183999
}

That's all that is needed to support registration of Users and managing tokens on their behalf. The source code also contains everything needed to support lost password and email verification. See previous posts for how to set it up.

In a typical deployment the authorization server and the resource server(s) would be separate, but for the purposes of this tutorial they are managed within the same application.
Let's delve into the details:

Web Context

There are two servlets.

A Jersey servlet as the default to handle all resource calls:

view plain print ?

<servlet-mapping>
<servlet-name>jersey-servlet</servlet-name>
<url-pattern>/*</url-pattern>
</servlet-mapping>

A Spring servlet to handle all oauth calls:

view plain print ?

<servlet-mapping>
<servlet-name>spring</servlet-name>
<url-pattern>/oauth/*</url-pattern>
</servlet-mapping>

Wire in spring security by defining a filter:

view plain print ?

<filter>
<filter-name>springSecurityFilterChain</filter-name>
<filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
<init-param>
<param-name>contextAttribute</param-name>
<param-value>org.springframework.web.servlet.FrameworkServlet.CONTEXT.spring</param-value>
</init-param>
</filter>

and then map it to the root context so all calls are filtered:

view plain print ?

<filter-mapping>
<filter-name>springSecurityFilterChain</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>

Configuring OAuth flows to support

view plain print ?

<oauth:authorization-server client-details-service-ref="client-details-service" token-services-ref="tokenServices">
<oauth:refresh-token/>
<oauth:password/>
</oauth:authorization-server>

In this scenario only password flow and refresh token are being supported. The default token endpoint is /oauth/token.

Protecting the token endpoint

It is a good idea to protect access to token requests to only those client applications that you know about. Using Spring security we can set up basic authentication on calls to the token endpoint:

view plain print ?

<http pattern="/oauth/token" create-session="stateless" authentication-manager-ref="clientAuthenticationManager"
xmlns="http://www.springframework.org/schema/security">
<anonymous enabled="false"/>
<http-basic entry-point-ref="clientAuthenticationEntryPoint"/>
<access-denied-handler ref="oauthAccessDeniedHandler"/>
</http>

Next we configure the authentication manager and client details service

view plain print ?

<bean id="clientCredentialsTokenEndpointFilter"
class="org.springframework.security.oauth2.provider.client.ClientCredentialsTokenEndpointFilter">
<property name="authenticationManager" ref="clientAuthenticationManager"/>
</bean>
<authentication-manager id="clientAuthenticationManager" xmlns="http://www.springframework.org/schema/security">
<authentication-provider user-service-ref="client-details-user-service"/>
</authentication-manager>
<bean id="client-details-user-service" class="org.springframework.security.oauth2.provider.client.ClientDetailsUserDetailsService">
<constructor-arg ref="client-details-service" />
</bean>

Depending on how many clients we expect to access the service will determine what type of client details service we implement. A simple file-based service might be sufficient. If you wanted to go a lot further with client sign up and managing API keys then you would have to involve a persistence tier for the client details service. Configuring with the default Spring file-based service is trivial:

view plain print ?

<oauth:client-details-service id="client-details-service">
<oauth:client
client-id="353b302c44574f565045687e534e7d6a"
secret="286924697e615a672a646a493545646c"
authorized-grant-types="password,refresh_token"
authorities="ROLE_TEST"
access-token-validity="${oauth.token.access.expiresInSeconds}"
refresh-token-validity="${oauth.token.refresh.expiresInSeconds}"
/>
<oauth:client
client-id="7b5a38705d7b3562655925406a652e32"
secret="655f523128212d6e70634446224c2a48"
authorized-grant-types="password,refresh_token"
authorities="ROLE_WEB"
access-token-validity="${oauth.token.access.expiresInSeconds}"
refresh-token-validity="${oauth.token.refresh.expiresInSeconds}"
/>
<oauth:client
client-id="5e572e694e4d61763b567059273a4d3d"
secret="316457735c4055642744596b302e2151"
authorized-grant-types="password,refresh_token"
authorities="ROLE_IOS"
access-token-validity="${oauth.token.access.expiresInSeconds}"
refresh-token-validity="${oauth.token.refresh.expiresInSeconds}"
/>
<oauth:client
client-id="302a7d556175264c7e5b326827497349"
secret="4770414c283a20347c7b553650425773"
authorized-grant-types="password,refresh_token"
authorities="ROLE_ANDROID"
access-token-validity="${oauth.token.access.expiresInSeconds}"
refresh-token-validity="${oauth.token.refresh.expiresInSeconds}"
/>
</oauth:client-details-service>

Accessing the oauth endpoint now requires a basic authentication header with the client id and secret concatenated with a ":" separator and base64 encoded.
e.g. -H "Authorization: Basic MzUzYjMwMmM0NDU3NGY1NjUwNDU2ODdlNTM0ZTdkNmE6Mjg2OTI0Njk3ZTYxNWE2NzJhNjQ2YTQ5MzU0NTY0NmM="

Configuring User Authentication Services

The Resource Owner Password flow requires an authentication manager for managing users.

view plain print ?

<bean id="passwordEncoder" class="org.springframework.security.crypto.password.StandardPasswordEncoder"/>
<sec:authentication-manager alias="userAuthenticationManager">
<sec:authentication-provider user-service-ref="userService">
<sec:password-encoder ref="passwordEncoder"/>
</sec:authentication-provider>
</sec:authentication-manager>

The password encoder is used to encrypt the password on authentication. The user service also uses the same encoder to encrypt passwords before persisting them.
The user service must implement UserDetailsService and retrieve the user by username.

view plain print ?

@Override
public UserDetails loadUserByUsername(String username) throws UsernameNotFoundException {
notNull(username, "Mandatory argument 'username' missing.");
User user = userRepository.findByEmailAddress(username.toLowerCase());
if (user == null) {
throw new AuthenticationException();
}
return user;
}

Configuring Token Services

The final piece of configuration is to manage storage and retrieval of access tokens.

view plain print ?

<bean id="tokenServices" class="org.springframework.security.oauth2.provider.token.DefaultTokenServices">
<property name="tokenStore" ref="tokenStore"/>
<property name="supportRefreshToken" value="true"/>
<property name="clientDetailsService" ref="client-details-service"/>
</bean>

Spring has a handy in-memory implementation that is useful when testing:

view plain print ?

<bean id="tokenStore" class="org.springframework.security.oauth2.provider.token.InMemoryTokenStore"/>

For this tutorial I have chosen MongoDB as the persistence technology, but it would be easy to wire in an alternative such as MySql or Redis It is a matter of implementing org.springframework.security.oauth2.provider.token.TokenStore

view plain print ?

<bean id="tokenStore" class="com.porterhead.oauth2.mongodb.OAuth2RepositoryTokenStore">
<constructor-arg ref="OAuth2AccessTokenRepository"/>
<constructor-arg ref="OAuth2RefreshTokenRepository"/>
</bean>

Protecting access to resources

First we need to configure a spring resource server filter. This will check that there is a valid access token in the request header.

view plain print ?

<oauth:resource-server id="resourceServerFilter" token-services-ref="tokenServices"/>

Spring security has some useful classes for fine-grain control of roles and permissions. I prefer to use JSR-250 annotations. Luckily it is easy to wire this in. First we need to enable JSR-250 annotations with the following configuration:

view plain print ?

<sec:global-method-security jsr250-annotations="enabled" access-decision-manager-ref="accessDecisionManager"/>

Configure an access manager that uses the Jsr250Voter

view plain print ?

<bean id="accessDecisionManager" class="org.springframework.security.access.vote.UnanimousBased">
<property name="decisionVoters">
<list>
<bean class="org.springframework.security.access.annotation.Jsr250Voter"/>
</list>
</property>
</bean>

Now we can protect REST resource methods with JSR-250 annotations such as @RolesAllowed

Trying it out

Typically the glue between the OAuth server and the application is a user identifier. When a client gets an access token for a user the next step is to typically load data related to that user. This will usually involve building a url with the userId as part of the path
i.e. /v1.0/users/{id}/someresource
A useful service to provide is a way to get user information based on the access token. The application can identify the user that owns the token and return information on that user to the client.

view plain print ?

@Path("/v1.0/me")
@Component
@Produces({MediaType.APPLICATION_JSON})
@Consumes({MediaType.APPLICATION_JSON})
public class MeResource extends BaseResource {
@RolesAllowed({"ROLE_USER"})
@GET
public ApiUser getUser(final @Context SecurityContext securityContext) {
User requestingUser = loadUserFromSecurityContext(securityContext);
if(requestingUser == null) {
throw new UserNotFoundException();
}
return new ApiUser(requestingUser);
}
protected User loadUserFromSecurityContext(SecurityContext securityContext) {
OAuth2Authentication requestingUser = (OAuth2Authentication) securityContext.getUserPrincipal();
Object principal = requestingUser.getUserAuthentication().getPrincipal();
User user = null;
if(principal instanceof User) {
user = (User)principal;
} else {
user = userRepository.findByEmailAddress((String)principal);
}
return user;
}
}

To test this out start up the application:

> ./gradlew tomcatRun

Execute the following curl statement, substituting the access token that was returned from the login curl above

> curl -v -X GET \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer [your token here]" \
  'http://localhost:8080/oauth2-provider/v1.0/me'

Using OAuth 2.0 to Access Google APIs

2015-06-18T22:30:00.001+05:30

Google APIs use the OAuth 2.0 protocol for authentication and authorization. Google supports common OAuth 2.0 scenarios such as those for web server, installed, and client-side applications.
To begin, obtain OAuth 2.0 client credentials from the Google Developers Console. Then your client application requests an access token from the Google Authorization Server, extracts a token from the response, and sends the token to the Google API that you want to access. For an interactive demonstration of using OAuth 2.0 with Google (including the option to use your own client credentials), experiment with the OAuth 2.0 Playground.
This page gives an overview of the OAuth 2.0 authorization scenarios that Google supports, and provides links to more detailed content. For details about using OAuth 2.0 for authentication, see OpenID Connect.

Basic steps

All applications follow a basic pattern when accessing a Google API using OAuth 2.0. At a high level, you follow four steps:

1. Obtain OAuth 2.0 credentials from the Google Developers Console.

Visit the Google Developers Console to obtain OAuth 2.0 credentials such as a client ID and client secret that are known to both Google and your application. The set of values varies based on what type of application you are building. For example, a JavaScript application does not require a secret, but a web server application does.

2. Obtain an access token from the Google Authorization Server.

Before your application can access private data using a Google API, it must obtain an access token that grants access to that API. A single access token can grant varying degrees of access to multiple APIs. A variable parameter called scope controls the set of resources and operations that an access token permits. During the access-token request, your application sends one or more values in the scope parameter.
There are several ways to make this request, and they vary based on the type of application you are building. For example, a JavaScript application might request an access token using a browser redirect to Google, while an application installed on a device that has no browser uses web service requests.
Some requests require an authentication step where the user logs in with their Google account. After logging in, the user is asked whether they are willing to grant the permissions that your application is requesting. This process is called user consent.
If the user grants the permission, the Google Authorization Server sends your application an access token (or an authorization code that your application can use to obtain an access token). If the user does not grant the permission, the server returns an error.
It is generally a best practice to request scopes incrementally, at the time access is required, rather than up front. For example, an app that wants to support purchases should not request Google Wallet access until the user presses the “buy” button; see Incremental authorization.

3. Send the access token to an API.

After an application obtains an access token, it sends the token to a Google API in an HTTP authorization header. It is possible to send tokens as URI query-string parameters, but we don't recommend it, because URI parameters can end up in log files that are not completely secure. Also, it is good REST practice to avoid creating unnecessary URI parameter names.
Access tokens are valid only for the set of operations and resources described in the scope of the token request. For example, if an access token is issued for the Google+ API, it does not grant access to the Google Contacts API. You can, however, send that access token to the Google+ API multiple times for similar operations.

4. Refresh the access token, if necessary.

Access tokens have limited lifetimes. If your application needs access to a Google API beyond the lifetime of a single access token, it can obtain a refresh token. A refresh token allows your application to obtain new access tokens.

Scenarios

Web server applications

The Google OAuth 2.0 endpoint supports web server applications that use languages and frameworks such as PHP, Java, Python, Ruby, and ASP.NET.
The authorization sequence begins when your application redirects a browser to a Google URL; the URL includes query parameters that indicate the type of access being requested. Google handles the user authentication, session selection, and user consent. The result is an authorization code, which the application can exchange for an access token and a refresh token.
The application should store the refresh token for future use and use the access token to access a Google API. Once the access token expires, the application uses the refresh token to obtain a new one.

For details, see Using OAuth 2.0 for Web Server Applications.

Installed applications

The Google OAuth 2.0 endpoint supports applications that are installed on devices such as computers, mobile devices, and tablets. When you create a client ID through the Google Developers Console, specify that this is an Installed application, then select Android, Chrome, iOS, or "Other" as the application type.
The process results in a client ID and, in some cases, a client secret, which you embed in the source code of your application. (In this context, the client secret is obviously not treated as a secret.)
The authorization sequence begins when your application redirects a browser to a Google URL; the URL includes query parameters that indicate the type of access being requested. Google handles the user authentication, session selection, and user consent. The result is an authorization code, which the application can exchange for an access token and a refresh token.
The application should store the refresh token for future use and use the access token to access a Google API. Once the access token expires, the application uses the refresh token to obtain a new one.

For details, see Using OAuth 2.0 for Installed Applications.

Client-side (JavaScript) applications

The Google OAuth 2.0 endpoint supports JavaScript applications that run in a browser.
The authorization sequence begins when your application redirects a browser to a Google URL; the URL includes query parameters that indicate the type of access being requested. Google handles the user authentication, session selection, and user consent.
The result is an access token, which the client should validate before including it in a Google API request. When the token expires, the application repeats the process.

For details, see Using OAuth 2.0 for Client-side Applications.

Applications on limited-input devices

The Google OAuth 2.0 endpoint supports applications that run on limited-input devices such as game consoles, video cameras, and printers.
The authorization sequence begins with the application making a web service request to a Google URL for an authorization code. The response contains several parameters, including a URL and a code that the application shows to the user.
The user obtains the URL and code from the device, then switches to a separate device or computer with richer input capabilities. The user launches a browser, navigates to the specified URL, logs in, and enters the code.
Meanwhile, the application polls a Google URL at a specified interval. After the user approves access, the response from the Google server contains an access token and refresh token. The application should store the refresh token for future use and use the access token to access a Google API. Once the access token expires, the application uses the refresh token to obtain a new one.

For details, see Using OAuth 2.0 for Devices.

Service accounts

Google APIs such as the Prediction API and Google Cloud Storage can act on behalf of your application without accessing user information. In these situations your application needs to prove its own identity to the API, but no user consent is necessary. Similarly, in enterprise scenarios, your application can request delegated access to some resources.
For these types of server-to-server interactions you need a service account, which is an account that belongs to your application instead of to an individual end-user. Your application calls Google APIs on behalf of the service account, and user consent is not required. (In non-service-account scenarios, your application calls Google APIs on behalf of end-users, and user consent is sometimes required.)
A service account's credentials, which you obtain from the Google Developers Console, include a generated email address that is unique, a client ID, and at least one public/private key pair. You use the client ID and one private key to create a signed JWT and construct an access-token request in the appropriate format. Your application then sends the token request to the Google OAuth 2.0 Authorization Server, which returns an access token. The application uses the token to access a Google API. When the token expires, the application repeats the process.

For details, see the service-account documentation.

Token expiration

You should write your code to anticipate the possibility that a granted token might no longer work. A token might stop working for one of these reasons:

The user has revoked access.
The token has not been used for six months.
The user account has exceeded a certain number of token requests.

There is currently a 25-token limit per Google user account. If a user account has 25 valid tokens, the next authentication request succeeds, but quietly invalidates the oldest outstanding token without any user-visible warning.
If you need to authorize multiple programs, machines, or devices, one workaround is to limit the number of clients that you authorize per user account to 15 or 20. If you are a Google Apps admin, you can create additional admin users and use them to authorize some of the clients.

Client libraries

The following client libraries integrate with popular frameworks, which makes implementing OAuth 2.0 simpler. More features will be added to the libraries over time.

Android : Building a Flexible UI

2015-06-18T21:59:00.001+05:30

When designing your application to support a wide range of screen sizes, you can reuse your fragments in different layout configurations to optimize the user experience based on the available screen space.
For example, on a handset device it might be appropriate to display just one fragment at a time for a single-pane user interface. Conversely, you may want to set fragments side-by-side on a tablet which has a wider screen size to display more information to the user.

Figure 1. Two fragments, displayed in different configurations for the same activity on different screen sizes. On a large screen, both fragments fit side by side, but on a handset device, only one fragment fits at a time so the fragments must replace each other as the user navigates.

The FragmentManager class provides methods that allow you to add, remove, and replace fragments to an activity at runtime in order to create a dynamic experience.

Add a Fragment to an Activity at Runtime

Rather than defining the fragments for an activity in the layout file—as shown in the previous lesson with the <fragment> element—you can add a fragment to the activity during the activity runtime. This is necessary if you plan to change fragments during the life of the activity.
To perform a transaction such as add or remove a fragment, you must use the FragmentManager to create a FragmentTransaction, which provides APIs to add, remove, replace, and perform other fragment transactions.
If your activity allows the fragments to be removed and replaced, you should add the initial fragment(s) to the activity during the activity's onCreate() method.
An important rule when dealing with fragments—especially when adding fragments at runtime—is that your activity layout must include a container View in which you can insert the fragment.
The following layout is an alternative to the layout shown in the previous lesson that shows only one fragment at a time. In order to replace one fragment with another, the activity's layout includes an empty FrameLayout that acts as the fragment container.
Notice that the filename is the same as the layout file in the previous lesson, but the layout directory does not have the large qualifier, so this layout is used when the device screen is smaller than large because the screen does not fit both fragments at the same time.
res/layout/news_articles.xml:

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/fragment_container"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

Inside your activity, call getSupportFragmentManager() to get a FragmentManager using the Support Library APIs. Then call beginTransaction() to create a FragmentTransaction and call add() to add a fragment.
You can perform multiple fragment transaction for the activity using the same FragmentTransaction. When you're ready to make the changes, you must call commit().
For example, here's how to add a fragment to the previous layout:

import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
public class MainActivity extends FragmentActivity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.news_articles);

        // Check that the activity is using the layout version with
        // the fragment_container FrameLayout
        if (findViewById(R.id.fragment_container) != null) {

            // However, if we're being restored from a previous state,
            // then we don't need to do anything and should return or else
            // we could end up with overlapping fragments.
            if (savedInstanceState != null) {
                return;
            }

            // Create a new Fragment to be placed in the activity layout
            HeadlinesFragment firstFragment = new HeadlinesFragment();
            
            // In case this activity was started with special instructions from an
            // Intent, pass the Intent's extras to the fragment as arguments
            firstFragment.setArguments(getIntent().getExtras());
            
            // Add the fragment to the 'fragment_container' FrameLayout
            getSupportFragmentManager().beginTransaction()
                    .add(R.id.fragment_container, firstFragment).commit();
        }
    }
}

Because the fragment has been added to the FrameLayout container at runtime—instead of defining it in the activity's layout with a <fragment> element—the activity can remove the fragment and replace it with a different one.

Replace One Fragment with Another

The procedure to replace a fragment is similar to adding one, but requires the replace() method instead of add().
Keep in mind that when you perform fragment transactions, such as replace or remove one, it's often appropriate to allow the user to navigate backward and "undo" the change. To allow the user to navigate backward through the fragment transactions, you must call addToBackStack() before you commit the FragmentTransaction.

Note: When you remove or replace a fragment and add the transaction to the back stack, the fragment that is removed is stopped (not destroyed). If the user navigates back to restore the fragment, it restarts. If you do not add the transaction to the back stack, then the fragment is destroyed when removed or replaced.

Example of replacing one fragment with another:

// Create fragment and give it an argument specifying the article it should show
ArticleFragment newFragment = new ArticleFragment();
Bundle args = new Bundle();
args.putInt(ArticleFragment.ARG_POSITION, position);
newFragment.setArguments(args);
FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
// Replace whatever is in the fragment_container view with this fragment,
// and add the transaction to the back stack so the user can navigate back
transaction.replace(R.id.fragment_container, newFragment);
transaction.addToBackStack(null);
// Commit the transaction
transaction.commit();

The addToBackStack() method takes an optional string parameter that specifies a unique name for the transaction. The name isn't needed unless you plan to perform advanced fragment operations using the FragmentManager.BackStackEntry APIs.

Adding Action Buttons

2015-06-18T21:55:00.002+05:30

The action bar allows you to add buttons for the most important action items relating to the app's current context. Those that appear directly in the action bar with an icon and/or text are known as action buttons. Actions that can't fit in the action bar or aren't important enough are hidden in the action overflow.

Figure 1. An action bar with an action button for Search and the action overflow, which reveals additional actions.

Specify the Actions in XML

All action buttons and other items available in the action overflow are defined in an XML menu resource. To add actions to the action bar, create a new XML file in your project's res/menu/ directory.
Add an <item> element for each item you want to include in the action bar. For example:

res/menu/main_activity_actions.xml

<menu xmlns:android="http://schemas.android.com/apk/res/android" >
    <!-- Search, should appear as action button -->
    <item android:id="@+id/action_search"
          android:icon="@drawable/ic_action_search"
          android:title="@string/action_search"
          android:showAsAction="ifRoom" />
    <!-- Settings, should always be in the overflow -->
    <item android:id="@+id/action_settings"
          android:title="@string/action_settings"
          android:showAsAction="never" />
</menu>

Download action bar icons

To best match the Android iconography guidelines, you should use icons provided in the Action Bar Icon Pack.

This declares that the Search action should appear as an action button when room is available in the action bar, but the Settings action should always appear in the overflow. (By default, all actions appear in the overflow, but it's good practice to explicitly declare your design intentions for each action.)
The icon attribute requires a resource ID for an image. The name that follows @drawable/ must be the name of a bitmap image you've saved in your project's res/drawable/ directory. For example, "@drawable/ic_action_search" refers to ic_action_search.png. Likewise, the title attribute uses a string resource that's defined by an XML file in your project's res/values/ directory, as discussed in Building a Simple User Interface.

Note: When creating icons and other bitmap images for your app, it's important that you provide multiple versions that are each optimized for a different screen density. This is discussed more in the lesson about Supporting Different Screens.

If your app is using the Support Library for compatibility on versions as low as Android 2.1, the showAsAction attribute is not available from the android: namespace. Instead this attribute is provided by the Support Library and you must define your own XML namespace and use that namespace as the attribute prefix. (A custom XML namespace should be based on your app name, but it can be any name you want and is only accessible within the scope of the file in which you declare it.) For example:

res/menu/main_activity_actions.xml

<menu xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:yourapp="http://schemas.android.com/apk/res-auto" >
    <!-- Search, should appear as action button -->
    <item android:id="@+id/action_search"
          android:icon="@drawable/ic_action_search"
          android:title="@string/action_search"
          yourapp:showAsAction="ifRoom"  />
    ...</menu>

Add the Actions to the Action Bar

To place the menu items into the action bar, implement the onCreateOptionsMenu() callback method in your activity to inflate the menu resource into the given Menu object. For example:

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu items for use in the action bar
    MenuInflater inflater = getMenuInflater();
    inflater.inflate(R.menu.main_activity_actions, menu);
    return super.onCreateOptionsMenu(menu);
}

Respond to Action Buttons

When the user presses one of the action buttons or another item in the action overflow, the system calls your activity's onOptionsItemSelected() callback method. In your implementation of this method, call getItemId() on the given MenuItem to determine which item was pressed—the returned ID matches the value you declared in the corresponding <item> element's android:id attribute.

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle presses on the action bar items
    switch (item.getItemId()) {
        case R.id.action_search:
            openSearch();
            return true;
        case R.id.action_settings:
            openSettings();
            return true;
        default:
            return super.onOptionsItemSelected(item);
    }
}

Add Up Button for Low-level Activities

Figure 4. The Up button in Gmail.

All screens in your app that are not the main entrance to your app (activities that are not the "home" screen) should offer the user a way to navigate to the logical parent screen in the app's hierarchy by pressing the Up button in the action bar.
When running on Android 4.1 (API level 16) or higher, or when using ActionBarActivity from the Support Library, performing Up navigation simply requires that you declare the parent activity in the manifest file and enable the Up button for the action bar.
For example, here's how you can declare an activity's parent in the manifest:

<application ... >
    ...
    <!-- The main/home activity (it has no parent activity) -->
    <activity
        android:name="com.example.myfirstapp.MainActivity" ...>
        ...
    </activity>
    <!-- A child of the main activity -->
    <activity
        android:name="com.example.myfirstapp.DisplayMessageActivity"
        android:label="@string/title_activity_display_message"
        android:parentActivityName="com.example.myfirstapp.MainActivity" >
        <!-- Parent activity meta-data to support 4.0 and lower -->
        <meta-data
            android:name="android.support.PARENT_ACTIVITY"
            android:value="com.example.myfirstapp.MainActivity" />
    </activity>
</application>

Then enable the app icon as the Up button by calling setDisplayHomeAsUpEnabled():

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_displaymessage);

    getSupportActionBar().setDisplayHomeAsUpEnabled(true);
    // If your minSdkVersion is 11 or higher, instead use:
    // getActionBar().setDisplayHomeAsUpEnabled(true);
}

Because the system now knows MainActivity is the parent activity for DisplayMessageActivity, when the user presses the Up button, the system navigates to the parent activity as appropriate—you do not need to handle the Up button's event

Setting Up the Action Bar

2015-06-18T21:52:00.002+05:30

In its most basic form, the action bar displays the title for the activity and the app icon on the left. Even in this simple form, the action bar is useful for all activities to inform users about where they are and to maintain a consistent identity for your app.

Figure 1. An action bar with the app icon and activity title.

Setting up a basic action bar requires that your app use an activity theme that enables the action bar. How to request such a theme depends on which version of Android is the lowest supported by your app. So this lesson is divided into two sections depending on which Android version is your lowest supported.

Support Android 3.0 and Above Only

Beginning with Android 3.0 (API level 11), the action bar is included in all activities that use the Theme.Holo theme (or one of its descendants), which is the default theme when either the targetSdkVersion or minSdkVersion attribute is set to "11" or greater.
So to add the action bar to your activities, simply set either attribute to 11 or higher. For example:

<manifest ... >
    <uses-sdk android:minSdkVersion="11" ... />
    ...</manifest>

Note: If you've created a custom theme, be sure it uses one of the Theme.Holo themes as its parent. For details, see Styling the Action Bar.

Now the Theme.Holo theme is applied to your app and all activities show the action bar. That's it.

Support Android 2.1 and Above

Adding the action bar when running on versions older than Android 3.0 (down to Android 2.1) requires that you include the Android Support Library in your application.
To get started, read the Support Library Setup document and set up the v7 appcompat library (once you've downloaded the library package, follow the instructions for Adding libraries with resources).
Once you have the Support Library integrated with your app project:

Update your activity so that it extends ActionBarActivity. For example:
```
public class MainActivity extends ActionBarActivity { ... }
```
In your manifest file, update either the <application> element or individual <activity> elements to use one of the Theme.AppCompat themes. For example:
```
<activity android:theme="@style/Theme.AppCompat.Light" ... >
```
Note: If you've created a custom theme, be sure it uses one of the Theme.AppCompat themes as its parent. For details, see Styling the Action Bar.

Now your activity includes the action bar when running on Android 2.1 (API level 7) or higher.
Remember to properly set your app's API level support in the manifest:

<manifest ... >
    <uses-sdk android:minSdkVersion="7"  android:targetSdkVersion="18" />
    ...</manifest>

Android: How to display image in text view

2015-02-22T17:16:00.002+05:30

While designing we may get a situation where we may have to display a image near text. For example

In Android, to display like this, we may use a Imageview followed by a Textview.

Drawable drawable= activity.getResources().getDrawable(R.drawable.lyb);//load image in drawable
drawable.setBounds(0,0,drawable.getIntrinsicWidth(),calRich.getIntrinsicHeight());//sepecify bounds
textView.setCompoundDrawables(null,null,calRich,null);//right image
textView.setCompoundDrawablePadding(5);// specify padding between image and text

Android rectangle with bottom right corner triangle

2015-02-22T16:34:00.001+05:30

To create rectangle with bottom right corner triangle for drop down background

<?xml version="1.0" encoding="utf-8"?>

<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
    <item>
        <shape>
            <solid android:color="#ffffff" />
            <stroke
                android:width="1dp"
                android:color="@color/background_gradient_top" />
            <padding
                android:bottom="1dp"
                android:left="1dp"
                android:right="1dp"
                android:top="1dp" />
        </shape>
    </item>
    <item android:bottom="5dp" android:right="5dp">
        <rotate
            android:fromDegrees="-45"
            android:toDegrees="0"
            android:pivotX="150%"
            android:pivotY="20%" >
            <shape
                android:shape="rectangle" >
                <solid android:color="@color/primary_dark_material_light" />
            </shape>
        </rotate>
    </item>
</layer-list>

India vs Pakistan ICC World Cup 2015 Live match

2015-02-12T21:28:00.003+05:30

Watch India vs Pakistan ICC World Cup 2015 Live match on Starsports

Android using font fgcolor in String tag

2015-02-11T10:05:00.005+05:30

Font tags can be used inside string tag to specify diffent colors in same string.

the usage as follows.

<string name="txt_string">NORMAL TEXT<
font color="red" fgcolor="#FFFF0000">COLORED TEXT</font></string>

ORA-00600: [4194], [a], [b] : Oracle shutdown immediate

2013-01-11T13:33:00.000+05:30

One of the servers having 2 single instance databases hosted on it,was having some I/O issue.The control files, redo log files and the data files for both the database were present on these two mount points.

Cause if this I/O issue, both the databases were down.The SysAdmin team, dismounted and then mounted back these two disk,and the I/O issue was no more.It was time to startup the database.One of the database started up successfully.The other one, started throwing ORA-00600: [4194], [38], [20]

Successfully onlined Undo Tablespace 29.
Sun May 16 01:52:16 2010
SMON: enabling tx recovery
Sun May 16 01:52:16 2010
Database Characterset is WE8ISO8859P1
Sun May 16 01:52:17 2010
Errors in file /disk1/oracle/admin/idcdb/udump/idc_ora_22161.trc:
ORA-00600: internal error code, arguments: [4194], [38], [20], [], [], [], [], []
Doing block recovery for file 66 block 213923
Block recovery from logseq 15340, block 64 to scn 5970802072110
Sun May 16 01:52:20 2010
Recovery of Online Redo Log: Thread 1 Group 4 Seq 15340 Reading mem 0
  Mem# 0: /disk1/oradata/redo/redolog6.log
  Mem# 1: /disk1/oradata/redo/redomlplx/redolog6a.log
Block recovery stopped at EOT rba 15340.66.16
Block recovery completed at rba 15340.66.16, scn 1390.797530529
Doing block recovery for file 66 block 361
Block recovery from logseq 15340, block 64 to scn 5970802071968
Sun May 16 01:52:20 2010
Recovery of Online Redo Log: Thread 1 Group 4 Seq 15340 Reading mem 0
  Mem# 0: /disk1/oradata/redo/redolog6.log
  Mem# 1: /disk1/oradata/redo/redomlplx/redolog6a.log
Block recovery completed at rba 15340.66.16, scn 1390.797530529
replication_dependency_tracking turned off (no async multimaster replication found)
Starting background process QMNC
QMNC started with pid=20, OS id=23281
Sun May 16 01:52:25 2010
Completed: ALTER DATABASE OPEN

After few minutes, the instance was terminated by PMON process

Errors in file /disk1/oracle/admin/idcdb/bdump/idc_mmon_21649.trc:
ORA-00600: internal error code, arguments: [4194], [38], [20], [], [], [], [], []
ORA-00600: internal error code, arguments: [4194], [38], [20], [], [], [], [], []
ORA-00600: internal error code, arguments: [4194], [38], [20], [], [], [], [], []
Sun May 16 01:52:31 2010
Errors in file /disk1/oracle/admin/idcdb/bdump/idc_pmon_21599.trc:
ORA-00600: internal error code, arguments: [4194], [9], [5], [], [], [], [], []
Sun May 16 01:52:31 2010
Errors in file /disk1/oracle/admin/idcdb/udump/idc_ora_24006.trc:
ORA-00600: internal error code, arguments: [4194], [54], [39], [], [], [], [], []
Sun May 16 01:52:32 2010
Errors in file /disk1/oracle/admin/idcdb/bdump/idc_pmon_21599.trc:
ORA-00600: internal error code, arguments: [4194], [9], [5], [], [], [], [], []
PMON: terminating instance due to error 472
Sun May 16 01:52:32 2010
DEBUG: Replaying xcb 0x47fb9e970, pmd 0x47fde0728 for failed op 8
Doing block recovery for file 66 block 293914
Block recovery from logseq 15340, block 76 to scn 5970802072130
Sun May 16 01:52:32 2010
Recovery of Online Redo Log: Thread 1 Group 4 Seq 15340 Reading mem 0
  Mem# 0: /disk1/oradata/redo/redolog6.log
  Mem# 1: /disk1/oradata/redo/redomlplx/redolog6a.log
Block recovery completed at rba 15340.78.16, scn 1390.797530691
Sun May 16 01:52:38 2010
Instance terminated by PMON, pid = 21599

As per MOS

DESCRIPTION: A mismatch has been detected between Redo records and rollback (Undo) records.
We are validating the Undo record number relating to the change being applied against the maximum undo record number recorded in the undo block.
This error is reported when the validation fails.
ARGUMENTS:
Arg [a] Maximum Undo record number in Undo block
Arg [b] Undo record number from Redo block
FUNCTIONALITY:
Kernel Transaction Undo called from Cache layer
IMPACT:
PROCESS FAILURE
POSSIBLE ROLLBACK SEGMENT CORRUPTION
SUGGESTIONS:This error may indicate a rollback segment corruption.
This may require a recovery from a database backup depending on the situation.

Now, it was time to come in action . Below is the workaround steps :-
1. Startup database in mount mode

 SQL> startup mount
ORACLE instance started.

Total System Global Area 4294967296 bytes
Fixed Size                  2078264 bytes
Variable Size            4160752072 bytes
Database Buffers          117440512 bytes
Redo Buffers               14696448 bytes
Database mounted.

2. Check the values for Undo related parameter

SQL> show parameter undo

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
undo_management                      string      AUTO
undo_retention                       integer     900
undo_tablespace                      string      UNDOTBS1

3. Change the UNDO_MANAGEMENT to ‘MANUAL’

SQL>
SQL> alter system set undo_management='MANUAL' scope=spfile;

4. As, the above parameter is a static one, bounce the database

SQL> shu immediate;
ORA-01109: database not open

Database dismounted.
ORACLE instance shut down.
SQL> startup
ORACLE instance started.

Total System Global Area 4294967296 bytes
Fixed Size                  2078264 bytes
Variable Size            4160752072 bytes
Database Buffers          117440512 bytes
Redo Buffers               14696448 bytes
Database mounted.
Database opened.

5. In the meantime, keep checking the alert log.Check if there is some error after opening the database successfully with undo_management set to manual.
6.If everything seems fine, then go ahead and create a new undo tablespace.

SQL> create undo tablespace UNDOTBS datafile '/disk1/oradata/idcdb/undotbs1.dbf' size 1G autoextend on;

Tablespace created.

SQL> show parameter undo

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
undo_management                      string      MANUAL
undo_retention                       integer     900
undo_tablespace                      string      UNDOTBS1
SQL>

7. Set the undo_tablespace to the new Undo Tablespace name and undo_management back to ‘AUTO’

SQL> alter system set undo_tablespace='UNDOTBS' scope=spfile;

System altered.

SQL> alter system set undo_management='AUTO' scope=spfile;

System altered.

8. Bounce the database

SQL> shu immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup
ORACLE instance started.

Total System Global Area 4294967296 bytes
Fixed Size                  2078264 bytes
Variable Size            4160752072 bytes
Database Buffers          117440512 bytes
Redo Buffers               14696448 bytes
Database mounted.
Database opened.

9. Check the Alert log for if any errors and check the undo parameters

SQL> show parameter undo

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
undo_management                      string      AUTO
undo_retention                       integer     900
undo_tablespace                      string      UNDOTBS

After this the database was open successfully without any error.

Configure Linux to use GUI Logins

2012-05-18T15:29:00.001+05:30

Follow the instructions provided in the following link

http://www.idevelopment.info/data/Unix/Linux/LINUX_ConfiguringXDMCPRedHatLinux.shtml

Oracle: Changing orcladmin password when expired

2012-01-24T18:28:00.001+05:30

Problem:
orcladmin & other admin user passwords expired

Solution
Follow the steps below:
- Startup the OIDADMIN console (Infrastructure $ORACLE_HOME/bin/oidadmin)
$ORACLE_HOME refers to the Infrastructure database.
- Login as "orcladmin" user. If the password has not been modified, then, it is the same as the
"ias_admin" password specified during installation.

After login, navigate as follows:
==> Entry Management
==> cn=OracleContext
==> dc=com
==> dc=oracle
==> dc=acme
==> cn = users
==> cn = <orcladmin>
==> scroll to the bottom of the screen and update "userpassword" field and APPLY.

Now you can able to login with new password.

Useful xls document for Unit Conversion, Age Calculator, Railway Train Chart, Mobile Info, Health, BMI, etc...

2011-12-29T18:31:00.001+05:30

https://docs.google.com/open?id=0B84D74aUQO5DOTA4NDkzZjQtZGNkYy00NWRmLTg2NzMtNjcwYzFiNmE3N2Ez

Building Enterprise Services with Drools Rule Engine

2011-12-29T16:46:00.001+05:30

Building Enterprise Services with Drools Rule Engine http://onjava.com/pub/a/onjava/2007/01/17/building-enterprise-services-with-drools-rule-engine.html

Asynchronous Support in Servlet 3.0

2011-12-29T15:51:00.000+05:30

One of the significant enhancements made in JSR 315: Java Servlet 3.0, is support for asynchronous processing. With this support, a servlet no longer has to wait for a response from a resource such as a database before its thread can continue processing, that is, the thread is not blocked. Previous to Servlet 3.0, asynchronous support in the Java EE web container was provided in a proprietary way — either through APIs built on top of the Servlet 2.5 API or through non-Servlet APIs or implementations.
In modern web applications there are times when you need to asynchronously handle some part of the request, so that the web container can continue serving other requests in a seamless fashion. One example is a chat room application. In this type of application you want to enable long-lived client connections with a servlet. You don't want a server thread to be blocked for a long period of time serving a request from a single client. You want the servlet to process a request from the client and then free up the server thread as quickly as possible for other work. In other words, you want the request to be processed and a response generated asynchronously.
With the upcoming release of the Servlet 3.0 specification, standard asynchronous support has been added to the Servlet API. This Tech Tip introduces the asynchronous support that has been added to the Servlet API in Java Servlet 3.0 technology. It also includes a sample application that demonstrates those features.
Asynchronous Support Features
The primary features of the asynchronous support in Servlet 3.0 are as follows.
Annotation Attributes
Servlet 3.0 introduces the use of annotations as an alternative to deployment descriptors for servlet-related configuration in a web application. Two of these annotations are @WebServlet, which defines a servlet, and @WebFilter, which defines a servlet filter. Both of these annotations include an attribute, asyncSupported. Setting the asyncSupported attribute to true, declares that the servlet or servlet filter supports asynchronous processing. For example, the following annotation defines a servlet in a web application and declares that the servlet supports asynchronous processing:

   @WebServlet(url="/foo" asyncSupported=true)

The asyncSupported attribute is needed to differentiate code written for synchronous processing from that written for use in an asynchronous context. In fact, for an application to use the asynchronous feature, the entire request processing chain must have the have this attribute set either through the annotation or in its deployment descriptor. An IllegalStateException will be thrown if an application tries to start an asynchronous operation and there is a servlet or servlet filter in the request processing chain that does not support asynchronous processing.
Servlet Request Methods
The support for asynchronous processing also includes new ServletRequest methods, such as startAsync(servletRequest, servletResponse), startAsync(), and getAsyncContext(). After you set the asyncSupported attribute in the request processing chain to support asynchronous processing, you call either the startAsync(servletRequest, servletResponse) or startAsync() method to make an asynchronous request. Here, for example, is a call that makes an asynchronous request:

   AsyncContext aCtx = req.startAsync(req, res);

The difference between the two startAsync method signatures is that the startAsync() method implicitly uses the original request and response, while the startAsync(servletRequest, servletResponse) method uses the request and response objects passed in the method call. The request and response passed in the call can be wrapped by filters or other servlets earlier in the request processing chain. Notice that the startAsync method returns an AsyncContext object — see AsyncContext Class for more details. The AsyncContext object is initialized appropriately with the request and response objects depending on the method used. You must exercise caution when wrapping the response and calling the no arguments signature of the startAsync() method. You could lose the data if any of data is written to the wrapped response and not flushed to the underlying response stream.
There are a few more methods in the ServletRequest class that are part of the support for asynchronous processing. These include isAsyncSupported() and isAsyncStarted() You can use these convenience methods in an application to determine if asynchronous operations are supported or started on a request.
AsyncContext Class
The AsyncContext class is a new class in Servlet 3.0 that provides the execution context for an asynchronous operation. The class provides a variety of methods that you can use to get access to the underlying request and response objects. For example, you can use the AsyncContext.dispatch(), AsyncContext.dispatch(path), or AsyncContext.dispatch(servletContext, path) method to dispatch the request to the container. Using any of the dispatch methods, enables the processing to return to the container after the asynchronous operation that was started on the ServletRequest is completed — for instance, after waiting for a call to a web service to return. These methods dispatch the request back to the container so you can use frameworks such as JavaServer Pages (JSP) to generate the response.

The dispatch() method, that is, the method with no arguments, forwards the request back to the original URL. Also, if a call to AsyncContext.dispatch or RequestDispatcher.forward occurs after an asynchronous context has been initialized, the dispatch() method forwards the request to the path for the AsyncContext or RequestDispatcher-related requests.
The dispatch(path) method forwards the request to the path relative to the context of the request.
The dispatch(ServletContext, path) method forwards the request to the path relative to the specified context. For example, here is a call that forwards the request back to the container so that the JSP framework can generate the response.

   ctx.dispatch("/render.jsp");

Another AsyncContext method, complete(), completes the asynchronous operation that was started on the request that was used to initialize this AsyncContext object. It closes the response that was used to initialize this AsyncContext object. You can call this method, for example, when the response generated by the asynchronous operation is complete. The container can also implicitly call this method if the application dispatches the request back to the container using the forward method with no subsequent startAsync call on the request.
Asynchronous Listener Class
Servlet 3.0 also adds a new listener class for asynchronous processing, AsyncListener. You can use this class in an application to get notified when asynchronous processing is completed, if a timeout has occurred, an error has occurred, or a subsequent call to startAsync has occurred. The following code snippet creates a new AsyncListener object and uses it to get notified when an asynchronous processing operation is completed .

   AsyncContext ac = req.startAsync();
   req.addAsyncListener(new AsyncListener() {
      public void onComplete(AsyncEvent event) throws IOException {
         ...
      }
   ...
   }

Notice that the parameter passed to the onComplete method is an AsyncEvent object. The AsyncEvent class is another new class provided as part of the Servlet 3.0 support for asynchronous processing. It represents an event that gets fired when the asynchronous operation initiated on a ServletRequest has completed, timed out, or produced an error.
A Simple Application That Uses the Asynchronous Support in Servlet 3.0
Now that you've seen the key features in the Servlet 3.0 support for asynchronous processing, let's look at a more complete example. The following shows the code for a simple web application. In the application, a servlet makes an asynchronous request to a web service, waits for the call to return, and then dispatches the request back to the container to render the result using JSP. Note that the complete code for servlet is not shown.

   @WebServlet("/foo" asyncSupported=true)
   public class MyServlet extends HttpServlet {
        public void doGet(HttpServletRequest req, HttpServletResponse res) {
            ...
            AsyncContext aCtx = request.startAsync(req, res);
            ScheduledThreadPoolExecutor executor = new ThreadPoolExecutor(10);
            executor.execute(new AsyncWebService(aCtx));
        }
   }

   public class AsyncWebService implements Runnable {
        AsyncContext ctx;
        public AsyncWebService(AsyncContext ctx) {
            this.ctx = ctx;
        }
        public void run() {
            // Invoke web service and save result in request attribute
            // Dispatch the request to render the result to a JSP.
            ctx.dispatch("/render.jsp");
   }
}

Sample Application
One of the sample applications provided with the Java EE 6 SDK is a chat application that uses the asynchronous support in Servlet 3.0.
To run the application, do the following:

If you haven't already done so, download the Java EE 6 SDK. Also be sure to have an installed version of the Java Platform Standard Edition (Java SE) 6 SDK.
Download the sample application, async-request-war.war
Start the GlassFish v3 application server that is packaged with the Java EE 6 SDK by entering the following command:
```
   <javaee_home>/bin/asadmin start-domain
```
where <javaee_home> is where you installed the Java EE 6 SDK.
Deploy the sample application by copying it to the <javaee_home>/domains/domain1/autodeploy directory.


Execute the application by opening two browser windows. For simplicity, let's call them say Browser A and Browser B.
 
Point both Browser A and Browser B to the URL http://localhost:8080/async_request_war. In response, you should see
  a chat user interface (UI) in each browser window. The UI presents a text area to view chat entries, a text field to
  enter a user ID, and a Login button.
In Browser A, enter a user name, say "userA", in the text field and click the Login button. You should see
  the following message appear in the text area:
   
   

         System Message:
      userA has joined.
   

   

   
   
   


You should also see a new text area for posting messages to the chat and a button labeled Post Message.
  
  

  Login as "userB" in Browser B. You should see the following message appear in both browser windows:
   
 

        System Message:
       userB has joined.
 

 

 
 
 


The text area for posting messages and the Post Message button should appear in Browser B.
  
  Now, you're ready to chat.
  


  
In Browser A, enter "Hello" in the text box and click the Post Message button.
  You should see the following message in both Browser A and Browser B:
    
    

           userA:
       Hello
    

    

    
    
    



In Browser B, enter "Hello" in the text box and click the Post Message button.
  You should see the following message in both Browser A and Browser B:
  
  

         userB:
       Hello




You can view the source code for the application in the <javaee_home>/samples/javaee6/web/servlet/async-request-war/src
directory.





Further Reading




For more information, see the following resources:







JSR 315: Java Servlet 3.0
Java Servlet Technology

Creating ZIP and JAR Files in Java

2011-12-29T15:48:00.003+05:30

ZIP files offer a packaging mechanism, allowing multiple files to be bundled together as one. Thus, when you need to download a group of files from the web, you can package them into one ZIP file for easier transport as a single file. The bundling can include additional information like directory hierarchy, thus preserving necessary paths for an application or series of resources once unbundled.
This tip will address three aspects of ZIP file usage:

creating them
adding files to them
compressing those added files

Creating Zip Streams

The ZipOutputStream offers a stream for compressing the outgoing bytes. There is a single constructor for ZipOutputStream, one that accepts another OutputStream:

public ZipOutputStream(OutputStream out)

If the constructor argument is the type FileOutputStream, then the compressed bytes written by the ZipOutputStream will be saved to a file. However, you aren't limited to using the ZipOutputStream with a file. You can also use the OutputStream that comes from a socket connection or some other non-file-oriented stream. Thus, for a file-oriented ZipOutputStream, the typical usage will look like this:

String path = "afile.zip"; 
FileOutputStream fos = new FileOutputStream(path);
ZipOutputStream zos = new ZipOutputStream(fos);

Adding Entries

Once created, you don't just write bytes to a ZipOutputStream. Instead, you need to treat the output stream as a collection of components. Each component of a ZipOutputStream is paired with a ZipEntry. It is this ZipEntry that you create and then add to the ZipOutputStream before actually writing its contents to the stream.

String name = ...; 
ZipEntry entry = new ZipEntry(name);
zos.putNextEntry(entry);
zos.write(<< all the bytes for entry >>);

Each entry serves as a marker in the overall stream, where you'll find the bytes related to the entry in the library file. After the ZIP file has been created, when you need to get the entry contents back, just ask for the related input stream:

ZipFile zip = new ZipFile("afile.zip"); 
ZipEntry entry = zip.getEntry("anEntry.name");
InputStream is = zip.getInputStream(entry);

Now that you've seen how to create the zip file and add entries to that file, it is important to point out that the java.util.zip libraries offer some level of control for the added entries of the ZipOutputStream. First, the order you add entries to the ZipOutputStream is the order they are physically located in the .zip file. You can manipulate the enumeration of entries returned back by the entries() method of ZipFile to produce a list in alphabetical or size order, but the entries are still stored in the order they were written to the output stream.

Compressing Files

Files added to a ZIP/JAR file are compressed individually. Unlike Microsoft CAB files which compress the library package as a whole, files in a ZIP/JAR file are each compressed or not compressed separately. Before adding a ZipEntry to the ZipOutputStream, you determine whether its associated bytes are compressed. The setMethod method of ZipEntry allows you to specify which of the two available compression formats to use. Use the STORED constant of ZipEntry to give you an uncompressed file and the DEFLATED setting for a compressed version. You cannot control the compression efficiency. That depends on the type of data in the associated entry. Straight text can be compressed to around 80% of its size quite easily, whereas MP3 or JPEG data will be compressed much less.
While you might think it obvious that everything should be compressed, it does take time to compress and uncompress a file. If the task of compressing is too costly a task to do at the point of creation, it may sometimes be better to just store the data of the whole file in a STORED format, which just stores the raw bytes. The same can be said of the time cost of uncompression. Of course, uncompressed files are larger, and you have to pay the cost with either higher disk space usage or bandwidth when transferring file. Keep in mind that you need to change the setting for each entry, not the ZipFile as a whole. However, it is more typical to compress or not compress a whole ZipFile, as opposed to different settings for each entry.
There is one key thing you need to know if you use the STORED constant for the compression method: you must explicitly set certain attributes of the ZipEntry which are automatically set when the entry is compressed. These are the size, compressed size, and the checksum of the entry's input stream. Assuming an input file, the size and compressed size can just be the file size. To compute the checksum, use the CRC32 class in the java.util.zip package. You cannot just pass in 0 or -1 to ignore the checksum value; the CRC value will be used to validate your input when creating the ZIP and when reading from it later.

ZipEntry entry = new ZipEntry(name);
entry.setMethod(ZipEntry.STORED);
entry.setCompressedSize(file.length());
entry.setSize(file.length());
CRC32 crc = new CRC32();
crc.update(<< all the bytes for entry >>); 
entry.setCrc(crc.getValue());
zos.putNextEntry(entry);

To demonstrate, the following program will combine a series of files using the STORED compression method. The first argument to the program will be the ZIP file to create. Remaining arguments represent the files to add. If the ZIP file to create already exists, the program will exit without modifying the file. If you add a non-existing file to the ZIP file, the program will skip the non-existing file, adding any remaining command line arguments to the created ZIP.

import java.util.zip.\*;
import java.io.\*;

public class ZipIt {
    public static void main(String args[]) throws IOException {
        if (args.length < 2) {
            System.err.println("usage: java ZipIt Zip.zip file1 file2 file3");
            System.exit(-1);
        }
        File zipFile = new File(args[0]);
        if (zipFile.exists()) {
            System.err.println("Zip file already exists, please try another");
            System.exit(-2);
        }
        FileOutputStream fos = new FileOutputStream(zipFile);
        ZipOutputStream zos = new ZipOutputStream(fos);
        int bytesRead;
        byte[] buffer = new byte[1024];
        CRC32 crc = new CRC32();
        for (int i=1, n=args.length; i < n; i++) {
            String name = args[i];
            File file = new File(name);
            if (!file.exists()) {
                System.err.println("Skipping: " + name);
                continue;
            }
            BufferedInputStream bis = new BufferedInputStream(
                new FileInputStream(file));
            crc.reset();
            while ((bytesRead = bis.read(buffer)) != -1) {
                crc.update(buffer, 0, bytesRead);
            }
            bis.close();
            // Reset to beginning of input stream
            bis = new BufferedInputStream(
                new FileInputStream(file));
            ZipEntry entry = new ZipEntry(name);
            entry.setMethod(ZipEntry.STORED);
            entry.setCompressedSize(file.length());
            entry.setSize(file.length());
            entry.setCrc(crc.getValue());
            zos.putNextEntry(entry);
            while ((bytesRead = bis.read(buffer)) != -1) {
                zos.write(buffer, 0, bytesRead);
            }
            bis.close();
        }
        zos.close();
    }
}

For More info Creating Zip & Jar Files in Java

Using Callable to Return Results From Runnables

2011-12-29T14:31:00.001+05:30

The Runnable interface has been around since the beginning of time for the Java platform. It allows you to define a task to be completed by a thread. As most people probably know already, it offers a single method run() that accepts no arguments and returns no values, nor can it throw any checked exceptions. If you need to get a value back from the now-completed task, you must use a method outside the interface and wait for some kind of notification message that the task completed. For example, the following demonstrates what you might do for just such a scenario:

Runnable runnable = ...;

Thread t = new Thread(runnable);

t.start();

t.join();

String value = someMethodtoGetSavedValue()

Nothing is inherently wrong with this code, but it can be done differently now, thanks to the Callable interface introduced in J2SE 5.0. Instead of having a run() method, the Callable interface offers a call() method, which can return an Object or, more specifically, any type that is introduced in the genericized form:

public interface Callable<V> {

V call() throws Exception;

}

Because you cannot pass a Callable into a Thread to execute, you instead use the ExecutorService to execute the Callable object. The service accepts Callable objects to run by way of the submit() method:

<T> Future<T> submit(Callable<T> task)

As the method definition shows, submitting a Callable object to the ExecutorService returns a Future object. The get() method of Future will then block until the task is completed. This is the equivalent of the join() call in the first example. Actually, it is the equivalent of both the join() call and the get value call as get() returns the value calculated by the Callable instance.

To demonstrate, the following example creates separate Callable instances for each word passed in on the command line and sums up their length. Each Callable will just calculate the sum of its individual word. The set of Future objects are saved to acquire the calculated value from each. If the order of the returned values needed to be preserved, a List could be used instead.

import java.util.\*;

import java.util.concurrent.\*;

public class CallableExample {

public static class WordLengthCallable

implements Callable {

private String word;

public WordLengthCallable(String word) {

this.word = word;

}

public Integer call() {

return Integer.valueOf(word.length());

}

public static void main(String args[]) throws Exception {

ExecutorService pool = Executors.newFixedThreadPool(3);

Set<Future<Integer>> set = new HashSet<Future≶Integer>>();

for (String word: args) {

Callable<Integer> callable = new WordLengthCallable(word);

Future<Integer> future = pool.submit(callable);

set.add(future);

}

int sum = 0;

for (Future<Integer> future : set) {

sum += future.get();

}

System.out.printf("The sum of lengths is %s%n", sum);

System.exit(sum);

}

The WordLengthCallable saves each word and uses the word's length as the value returned by the call() method. This value could take some time to generate but in this case is known immediately. The only requirement of call() is the value is returned at the end of the call. When the get() method of Future is later called, the Future will either have the value immediately if the task runs quickly, as in this case, or will wait until the value is done generating. Multiple calls to get() will not cause the task to be rerun in the thread.

Because the goal of the program is to calculate the sum of all word lengths, it doesn't matter in which order the Callable tasks finish. It is perfectly OK if the last task completes before the first three. The first get() call to Future will just wait for the first task in the Set to complete. This does not block other tasks from running to completion separately. It is just waiting for that one thread or task to complete.

For more information on the use of executors and thread pools, see the Executors lesson in the Java Tutorial.

Using Generics With Wildcards and Extends

2011-12-29T14:21:00.001+05:30

J2SE 5.0 introduced generics to the Java programming. Generics allow for the identification of what you want to store in a collection. So instead of saying that your program has a List of Objects, you can now specify that you have a List of String objects or some other class type. Then, if you accidentally try to add something to the List that is of the wrong type, the compiler notifies you of the error and it can be fixed at compile time, rather than having to wait until you run the program and the program reaches the point in code where the fetch operation produces a runtime casting exception. Iterators now become typesafe. The next() method of the Iterator interface returns the typesafe version of the next element of the collection.

Most people don't fully understand the use of the extends keyword when using generics. A typical example shown to explain the use of extends has to do with drawing shapes. Instead, this tech tip will use an example that uses Swing components so that you do not have to create extra new classes. In a very limited case, the class hierarchy for Swing button components is shown here, with Object as the real root:

Component

|- Container

|- JComponent

|- AbstractButton

|- JButton

|- JMenuItem

|- JCheckBoxMenuItem

|- JMenu

|- JRadioButtonMenuItem

|- JToggleButton

|- JCheckBox

|- JRadioButton

One thing that all AbstractButton subclasses share in common is a getText() method. So in the spirit of generics, you can define a method that takes a List of AbstractButton items and return a List of the String labels of those buttons. Here's the first version of such a method:

public static List<String> getLabels(List<AbstractButton> list) {

List<String> labelList = new ArrayList<String>(list.size());

for (AbstractButton button: list) {

labelList.add(button.getText());

}

return labelList;

}

And here is how you might use the method. First, define a List of AbstractButton types, fill it up, and call the method:

List<AbstractButton> buttonList =

new ArrayList<AbstractButton>();

buttonList.add(new JButton("Hello"));

buttonList.add(new JCheckBox("World"));

buttonList.add(new JRadioButton("Hola"));

buttonList.add(new JMenuItem("Mundo"));

List labels = getLabels(buttonList);

System.out.println(labels);

"Hola, Mundo" is the Spanish translation of "Hello, World," according to Google. The results of the println() call is as follows:

[Hello, World, Hola, Mundo]

With a List of AbstractButtons, everything functions fine, but this breaks down when the List is of something else, specifically a subclass. One would logically think that with a List of JButton items, everything would work fine, because JButton is a subclass of AbstractButton. Shouldn't you be able to call getLabels(List<AbstractButton>) with a List of a subclass of AbstractButton?

List<JButton> buttonList = ...

// ... Fill list ...

List<String> labels = getLabels(buttonList);

Well, that isn't the case. Because this is a compile-time check, and because the definition of getLabels() is defined to accept only an AbstractButton List, you cannot pass anything else to it. The compilation-time error message follows:

GetList.java:13: getLabels(java.util.List<javax.swing.AbstractButton>)

in GetList cannot be applied to (java.util.List<javax.swing.JButton>)

List<String> labels = getLabels(buttonList);

1 error

And this is where the extends keyword comes in handy. Instead of defining the getLabels() method to accept only an AbstractButton list, define it to accept any List of AbstractButton subclasses:

public static List<String> getLabels(

List<? extends AbstractButton> list) {

The wildcard ? here says that the method doesn't care what the exact class type is, as long as it is a subclass of AbstractButton. Here's a complete example that puts all the pieces together:

import java.util.\*;

import javax.swing.\*;

public class GetList {

public static void main(String args[]) {

List<JButton> buttonList =

new ArrayList<JButton>();

buttonList.add(new JButton("Hello"));

buttonList.add(new JButton("World"));

buttonList.add(new JButton("Hola"));

buttonList.add(new JButton("Mundo"));

List labels = getLabels(buttonList);

System.out.println(labels);

}

public static List<String> getLabels(

List<? extends AbstractButton> list) {

List<String> labelList = new ArrayList<String>(list.size());

for (AbstractButton button: list) {

labelList.add(button.getText());

}

return labelList;

}

Now, when you are defining your own classes and methods with generics and are thinking of accepting an abstract class as the generic argument, or any superclass, remember to use wildcards so that the same method works best with subclasses too.

Oracle 11g R2 Recovering database on Solaris 10 : ORA-00600: internal error code, arguments: [kcratr_nab_less_than_odr]

2011-12-29T11:37:00.001+05:30

ORA-00600: internal error code, arguments: [kcratr_nab_less_than_odr]

I have an Oracle 11g R2 database on a Solaris 10. I got this error many times, it was due to Solaris illegal shutdown.

Here are the steps I performed to resolve this error

Launch SQL Plus from Oracle\bin folder ( not from Client folder)

SQL> conn sys/sys as sysdba

Connected to an idle instance.

SQL> startup mount

ORACLE instance started.

SQL> alter database recover;

Database altered.

SQL> alter database open;

alter database open

*

ERROR at line 1:

ORA-00600: internal error code, arguments: [kcratr_nab_less_than_odr], [1],

[136], [65730], [65738], [], [], [], [], [], [], []

SQL> shutdown immediate;

ORACLE instance shut down.

SQL> startup mount

ORACLE instance started.

SQL> alter database recover until cancel using backup controlfile;

alter database recover until cancel using backup controlfile

*

ERROR at line 1:

ORA-00279: change 3997604 generated at 02/11/2011 21:08:59 needed for thread 1
ORA-00289: suggestion :
C:\APP\RMANNI\RECOVERY_AREA\ORCLDB11G\ARCHIVELOG\2011_02_14\O1_MF_1_136_%U_.ARC
ORA-00280: change 3997604 for thread 1 is in sequence #136

Since my database is not running in archive log mode, I couldn't find the file specified in the above error message. I proceeded with the following

SQL> alter database recover continue default;

alter database recover continue default

*

ERROR at line 1:

ORA-00308: cannot open archived log

'C:\APP\RMANNI\RECOVERY_AREA\ORCLDB11G\ARCHIVELOG\2011_02_14\O1_MF_1_136_%U_.ARC'

ORA-27041: unable to open file

OSD-04002: unable to open file

O/S-Error: (OS 2) The system cannot find the file specified.

SQL> alter database recover cancel;

Database altered.

If the above step errored out, then proceed with the lines shown below inbetween the dotted lines, if not

SQL> alter database open resetlogs;

Database altered.

SQL> Your database is good to go, You should now be able to connect

-----------If Alter database recover cancel Failed ------------------

SQL> alter database recover cancel;

alter database recover cancel

*

ERROR at line 1:

ORA-10879: error signaled in parallel recovery slave

ORA-01547: warning: RECOVER succeeded but OPEN RESETLOGS would get error below

ORA-01194: file 1 needs more recovery to be consistent

ORA-01110: data file 1: 'C:\APP\RMANNI\ORADATA\ORCLDB\SYSTEM01.DBF'

SQL> recover database using backup controlfile until cancel;

ORA-00275: media recovery has already been started

SQL> shutdown immediate;

ORACLE instance shut down.

SQL> startup mount

ORACLE instance started.

Now, when you try to recover, Oracle will provide a suggestion,provide the path for your REDO log files. One of the log files will fix your database. I started with Redo03, but Redo01 fixed my database. You probably don't need to shutdown and restart the database for each Redo log flies.

SQL> recover database using backup controlfile until cancel;

ORA-00279: change 2448238 generated at 11/16/2010 22:05:53 needed for thread 1

ORA-00289: suggestion :

C:\APP\RMANNI\FLASH_RECOVERY_AREA\ORCLDB\ARCHIVELOG\2011_02_14\O1_MF_1_67_%U_.ARC

ORA-00280: change 2448238 for thread 1 is in sequence #67

Specify log: {=suggested
filename
AUTO
CANCEL}

C:\app\rmanni\oradata\ORCLDB\REDO03.LOG

ORA-00310: archived log contains sequence 66; sequence 67 required

ORA-00334: archived log: 'C:\APP\RMANNI\ORADATA\ORCLDB\REDO03.LOG'

ORA-10879: error signaled in parallel recovery slave

ORA-01547: warning: RECOVER succeeded but OPEN RESETLOGS would get error below

ORA-01194: file 1 needs more recovery to be consistent

ORA-01110: data file 1: 'C:\APP\RMANNI\ORADATA\ORCLDB\SYSTEM01.DBF'

SQL> shutdown immediate;

ORACLE instance shut down.

SQL> startup mount

ORACLE instance started.

SQL> recover database using backup controlfile until cancel;

ORA-00279: change 2448238 generated at 11/16/2010 22:05:53 needed for thread 1

ORA-00289: suggestion :

C:\APP\RMANNI\FLASH_RECOVERY_AREA\ORCLDB\ARCHIVELOG\2011_02_14\O1_MF_1_67_%U_.ARC

ORA-00280: change 2448238 for thread 1 is in sequence #67

Specify log: {=suggested filename AUTO CANCEL}

C:\app\rmanni\oradata\ORCLDB\REDO02.LOG

ORA-00310: archived log contains sequence 65; sequence 67 required

ORA-00334: archived log: 'C:\APP\RMANNI\ORADATA\ORCLDB\REDO02.LOG'

ORA-10879: error signaled in parallel recovery slave

ORA-01547: warning: RECOVER succeeded but OPEN RESETLOGS would get error below

ORA-01194: file 1 needs more recovery to be consistent

ORA-01110: data file 1: 'C:\APP\RMANNI\ORADATA\ORCLDB\SYSTEM01.DBF'

SQL> Shutdown immediate;

ORACLE instance shut down.

SQL> startup mount;

ORACLE instance started.

SQL> recover database using backup controlfile until cancel;

ORA-00279: change 2448238 generated at 11/16/2010 22:05:53 needed for thread 1

ORA-00289: suggestion :

C:\APP\RMANNI\FLASH_RECOVERY_AREA\ORCLDB\ARCHIVELOG\2011_02_14\O1_MF_1_67_%U_.ARC

ORA-00280: change 2448238 for thread 1 is in sequence #67

Specify log: {=suggested filename AUTO CANCEL}

C:\app\rmanni\oradata\ORCLDB\REDO01.log

Log applied.

Media recovery complete.

SQL> alter database open resetlogs;

Database altered.

-----------If Alter database recover cancel Failed ------------------

Word of the day

2011-12-29T11:31:00.001+05:30

bespectacled adj

Wearing spectacles (glasses).

Step by step installation of oracle on Solaris 10

2011-12-29T10:59:00.001+05:30

Oracle installation

1. /usr/sbin/groupadd oinstall
2. /usr/sbin/groupadd dba
3. /usr/sbin/groupadd oper
4. mkdir /export/home/oracle
5. /usr/sbin/useradd -g oinstall -G dba,oper -d /export/home/oracle oracle
6. chown oracle:oinstall /export/home/oracle
7. mkfile 5gb /tempswap
8. swap -a /tempswap
9. prctl -n project.max-shm-memory -v 6gb -r -i project default
10 connect to oracle user
11. ./runInstaller

Jersey Restful Webservices API document automation using maven

2011-12-29T10:58:00.001+05:30

1. 1. Include following configuration in pom.xml

<id>release</id>

<build>

<groupId>org.apache.maven.plugins</groupId>

<artifactId>maven-javadoc-plugin</artifactId>

<links>

</links>

</configuration>

</plugin>

</plugins>

</build>

</profile>

</profiles>

<groupId>org.apache.maven.plugins</groupId>

<artifactId>maven-javadoc-plugin</artifactId>

<goals>

<goal>javadoc</goal>

</goals>

<phase>package</phase>

</execution>

</executions>

<verbose>false</verbose>

<show>public</show>

<subpackages>com.abc.webservices</subpackages>

<doclet>com.sun.jersey.wadl.resourcedoc.ResourceDoclet</doclet>

<groupId>com.sun.jersey.contribs</groupId>

<artifactId>wadl-resourcedoc-doclet</artifactId>

<version>${jersey-release-version}</version>

</docletArtifact>

<!--

Also specify jersey and xerces as doclet artifacts as the ResourceDoclet

uses classes provided by them to generate the resourcedoc.

-->

<groupId>com.sun.jersey</groupId>

<artifactId>jersey-server</artifactId>

<version>${jersey-release-version}</version>

</docletArtifact>

<groupId>xerces</groupId>

<artifactId>xercesImpl</artifactId>

</docletArtifact>

</docletArtifacts>

<additionalparam>-output ${project.build.outputDirectory}/resourcedoc.xml</additionalparam>

</configuration>

</plugin>

<groupId>com.sun.jersey.contribs</groupId>

<artifactId>maven-wadl-plugin</artifactId>

<version>${jersey-release-version}</version>

<id>generate</id>

<goals>

<goal>generate</goal>

</goals>

<phase>package</phase>

</execution>

</executions>

<wadlFile>${project.build.outputDirectory}/application.wadl</wadlFile>

<baseUri>http://localhost:8080/api</baseUri>

<param>com.abc.webservices</param>

</packagesResourceConfig>

<className>com.sun.jersey.server.wadl.generators.WadlGeneratorApplicationDoc</className>

<name>applicationDocsFile</name>

<value>${basedir}/src/main/resources/application-doc.xml</value>

</property>

</properties>

</wadlGeneratorDescription>

<className>com.sun.jersey.server.wadl.generators.WadlGeneratorGrammarsSupport</className>

<name>grammarsFile</name>

<value>${basedir}/src/main/resources/application-grammars.xml</value>

</property>

</properties>

</wadlGeneratorDescription>

<className>com.sun.jersey.server.wadl.generators.resourcedoc.WadlGeneratorResourceDocSupport</className>

<name>resourceDocFile</name>

<value>${project.build.outputDirectory}/resourcedoc.xml</value>

</property>

</properties>

</wadlGeneratorDescription>

</wadlGenerators>

</configuration>

</plugin>

<groupId>org.codehaus.mojo</groupId>

<artifactId>xml-maven-plugin</artifactId>

<goals>

<goal>transform</goal>

</goals>

<phase>package</phase>

</execution>

</executions>

<dir>${project.build.outputDirectory}</dir>

<include>application.wadl</include>

</includes>

<stylesheet>${basedir}/src/main/resources/wadl_documentation.xsl</stylesheet>

<outputDir>${project.build.directory}</outputDir>

</fileMapper>

</fileMappers>

</transformationSet>

</transformationSets>

</configuration>

<groupId>net.sf.saxon</groupId>

<artifactId>saxon</artifactId>

</dependency>

</dependencies>

</plugin>

</plugins>

2. Copy application-doc.xml, application-grammars.xml and wadl_documentation.xsl in src/main/resources directory
3. Run mvn clean install

InfoAlly

Android: Adding easy share

Using lists in Android (ListView) - Tutorial

1.1. Using lists in Android

1.2. Views for handling lists

1.3. Possible input types for lists

1.4. Adapters

Tip

1.5. Filtering and sorting

1.6. Data updates in the adapter

1.7. Listener

2. Default adapter

2.1. Default platform adapter

2.2. Using ArrayAdapter

Warning

2.3. ListView example with ArrayAdapter

3. Custom adapter implementations

3.1. Developing a custom adapter

Tip

3.2. Preparing a row for the list

Note

3.3. Example for a custom adapter

3.4. Updating the data model from the adapter

4. ListActivity and ListFragment

4.1. Default container for using ListView

4.2. ListActivity and custom layout

Warning

4.3. Placeholder for an empty list

5. Exercise: Using ListView and ListActivity

6. Exercise: ListActivity with own layout

7. Tutorial: Implementing your own adapter

8. ListViews and performance

8.1. Motivation

8.2. Time consuming operations

8.3. Avoiding layout inflation and object creation

8.4. View holder pattern

8.5. Example

9. Storing the selection of a view

10. Contextual action mode for ListViews

11. Implementing undo for an action

11.1. When should you offer an undo action?

11.2. Example

12. Performance Optimization

13. Tutorial: How to display two items in a ListView

14. Selecting multiple items in the ListView

14.1. Interaction between the model and Listview

14.2. Tutorial: Domain Model and Rows interaction

15. Implementing an expandable ListView

15.1. ExpandableListView

15.2. ExpandableListView example

16. Tutorial: Miscellaneous

16.1. Adding a longclick listener to the list items

16.2. Header and Footer

17. SimpleCursorAdapter

AngularJS - REST Services

Dependencies

Template

Service

Controller

Test

Securing REST Services with Spring Security and OAuth2

Resource Owner Password Flow

Building the project

Running the Web Application

Testing with Curl

Web Context

Configuring OAuth flows to support

Protecting the token endpoint

Configuring User Authentication Services

Configuring Token Services

Protecting access to resources

Trying it out

Using OAuth 2.0 to Access Google APIs

Contents

Basic steps

1. Obtain OAuth 2.0 credentials from the Google Developers Console.

2. Obtain an access token from the Google Authorization Server.

3. Send the access token to an API.

4. Refresh the access token, if necessary.

Scenarios