Java Talks

How to upload an artifact to maven remote repository?

2011-10-17T02:27:00.000-07:00

If you want to deploy artifacts that were not build using maven, or which were build using maven but their POMs did not contains the deployment detials, then you need to deploy them using the following:

mvn -e deploy:deploy-file
-DgroupId=com.test.jpa
-DartifactId=jpa-demo
-Dversion=1.0.0
-Dpackaging=jar
-Dfile=jpa-demo-1.0.0.jar
-Durl=http://localhost:8080/archiva/repository/internal/
-DrepositoryId=reppoId

url: specifies the remote maven repository to where the jar is to be uploaded
repositoryId: Id repository is secured, repositoryId is used to specify the credentials that are to be used for uploading. Repositories are defined in settings.xml.
e.g.
<servers>
    <server>
      <id>deploymentRepo</id>
      <username>repouser</username>
      <password>repopwd</password>
    </server>
</servers>

Maven repository will return code 401 if credentials are missing or invalid.

Better way is to use deploy phase of the default build lifecycle. For that include a valid <distributionManagement/> section in project's pom.xml and define the remote repository using <repository/>.

If the repository is secured, you should configure your settings.xml file to define corresponding <server/> entries which provides authentication information.

pom.xml

...
<distributionManagement>
    <repository>
      <id>my.internal.repo</id>
      <name>Internal Repository</name>
      <url>http://...</url>
    </repository>
</distributionManagement>
...

settings.xml

...
<server>
      <id>my.internal.repo</id>
      <username>user</username>
      <password>pass</password>
</server>
...

maven deploy will not deploy the artifact to your remote repository.

Error validating server certificate / The certificate is not issued by a trusted authority

2011-08-01T01:06:00.000-07:00

I was able to use SVN with ease (checkin, checkout, update code) until recently the SVN server went through some changes. I started to see the following on each SVN command:

Error validating server certificate for 'https://svn.myserver.com:443':
- The certificate is not issued by a trusted authority. Use the
fingerprint to validate the certificate manually!
- The certificate hostname does not match.
Certificate information:
- Hostname: de-v-svn
- Valid: from ...
- Issuer: I...
- Fingerprint: ...
(R)eject, accept (t)emporarily or accept (p)ermanently?

It worked fine when I selected (p)ermanently but had to do it again next time I used SVN command.

Solution:
Delete ~/.subversion folder.
svn cleanup
svn up

log4j - use logger instead of category

2011-07-19T07:44:00.000-07:00

Do not use 'category'.

In log4j 1.2, the Category class has marked as being deprecated and has been replaced by the Logger class. I am using log4j-1.2.14.jar and category didn't work for me.

Example:

Was:

GlassFish Server - Full Profile vs Web Profile

2011-06-17T11:06:00.000-07:00

When you are about to download Glassfish server 3.x, you need to decide you want to download Full Profile or Web Profile version.

View the differences.

svn credentials caching

2011-01-03T02:01:00.000-08:00

SVN client has a built-in system for caching authentication credentials on disk. It saves the credentials in the user's private runtime configuration area

~/.subversion/auth/ (Unix-like systems)
%APPDATA%/Subversion/auth/ (Windows)

If you dont want to catch the credeitials for a commit, use --no-auth-cache.
$ svn commit --no-auth-cache

Here we are telling the svn client that dont cach authentication credentials.

You can disable credential caching permanently by editing your runtime config file (located next to the auth/ directory). Set store-auth-creds to no.

[auth]
store-auth-creds = no

Comparable interface

2010-08-25T04:43:00.000-07:00

Lists and Arrays of objects that implement Comparable interface can be sorted automatically by Collections.sort and Arrays.sort respectively.

Implementation Comparable is easy. You just have to implement compareTo(Object o). It should return negative integer, zero, or a positive integer as this object is less than, equal to,or greater than the specified object.

Here goes an example:

public void testListSort(){

Calendar cal = Calendar.getInstance();
cal.set(2010, 10, 1);
License msWindows7 = new License("Windows", "7",new Date(cal.getTimeInMillis()));
cal.clear();
cal.set(2010, 11, 10);
License msWindowsVista = new License("Windows", "Vista", new Date(cal.getTimeInMillis()));
cal.clear();
cal.set(2010, 11, 5);
License lotusNotes = new License("Notes", "1.1", new Date(cal.getTimeInMillis()));

List list = new ArrayList(3);

list.add(lotusNotes);
list.add(msWindowsVista);
list.add(msWindows7);

Collections.sort(list);

for(License l : list){
System.out.println(l);
}
}

private class License implements Comparable{
String id;
String version;
Date expiryDate;

public License(String id, String version,
Date expiryDate) {
this.id = id;
this.version = version;
this.expiryDate = expiryDate;
}

@Override
public int compareTo(License license) {
// Returns a negative integer, zero, or a positive integer as this object is less than,
// equal to,or greater than the specified object.

if(this.expiryDate.after(license.expiryDate)){
return 1;
}
else{
return 0;
}
}

@Override
public String toString(){
return "id: " + id + "\n" +
"version: " + version + "\n" +
"expiryDate: " + expiryDate + "\n\n";
}
}

Your comments are welcome as always :)

desending sort algo

2010-08-25T03:00:00.000-07:00

...
double []test = new double []{88.6,88.9,-1,25,88.6};
int size = test.length;

System.out.println("*** un-sorted ***");
for (double d : test){
System.out.println(d);
}

// descending sort algo *************************************
int counter = 0;
int indexOfMax = 0;

// after each iteration of while, test[counter] should have the correct value
while (counter < size){
indexOfMax = counter; // assuming that test[counter] has the max value
// this loop finds the index of max value (stores in indexOfMax) from the test array starting from index counter+1
for(int i = counter+1; i < size; i++){
if (test[i]>test[indexOfMax]){
indexOfMax = i;
}
} // end of for loop -- now indexOfMax should have the max value

// swapping
double tmp = test[counter];
test[counter] = test[indexOfMax];
test[indexOfMax] = tmp;
counter++;
}
// end of algo *********************************************

System.out.println("*** sorted ***");
for (double d : test){
System.out.println(d);
}
...

relocating/switching SVN repository

2010-08-02T05:05:00.000-07:00

My SVN repository changed recently and I was worried about associating my Java workspace with the new repository . Checking out from the new repository was always an option but of course, I would have lost my non committed changes.

After googling for half an hour, I found a way to switch my SVN repository.

1. Find the current repository's URL to which your files/folders are associated.
svn info

2. Switch the repo.
svn switch --relocate

3. Verify the current repo's URL.
svn info

Hope this helps.

Useful SVN commands

2010-08-02T04:37:00.000-07:00

svn info
Print information about paths in your working copy.

svn status / svn st
Print the status of working copy files and directories.

svn update / svn up
updates the working copy.

svn commit -m "message goes here" / svn ci
Send changes from your working copy to the repository

svn log -l 10
Prints last 10 commits in reverse-chronological order by default.

SVN red book

2010-06-09T01:51:00.000-07:00

I normally use Subclipse plugin for Eclipse for SVN operations. It really makes life easy. I am a novice when it comes to performing svn operations using SVN commands.

I found a very useful resource for that:

HTML version of SVN red book (for subversion 1.5)

Hope you find this useful :)

Tomcat for J2EE

2010-03-02T07:26:00.000-08:00

Apache Tomcat now supports J2EE applications.

JAR search engine

2009-09-01T02:47:00.000-07:00

I have been using FindJar which is a JAR search engine that helps to find JAR files containing required Java classes. Try it out.

Parameter vs Argument

2009-06-30T11:16:00.000-07:00

The parameter is the local variable in the method and the argument is the caller-supplied value/reference.

In the given example, the parameter for doSomething is 'a' and the argument is 22.

public static void doSomething(int a)
{
System.out.println("The argument was " + a);
}

public static void main(String[] s)
{
doSomething(22);
}

measurement of code quality - WTF’s/minute

2009-04-17T01:46:00.000-07:00

An Interesting article about how WTFs can improve Code quality in a team

How WTF’s improve code quality awareness

SCJP resource (Kathy Sierra's EBook)

2009-03-22T12:58:00.000-07:00

One of the best resource for SCJP is Kathy Sierra's Java 5 EBook.

Download from RapidShare

Autoboxing example

2009-03-13T02:02:00.000-07:00

You can’t put a primitive value into a collection since collections can only hold object references. To do so, you need to box primitive values into the appropriate wrapper class. When retriving, you get an object out of the collection and you need to unbox the it. Java 5 provides autoboxing and unboxing feature that eliminates the pain.

 import java.util.ArrayList;
   
     public class Autoboxing {
       public static void main(String[] args) {
           ArrayList list = new ArrayList();
           for(int i = 0; i < 10; i++){
              list.add(i);
           }
           int sum = 0;
          for ( Integer j : list){
            sum += j;
          }
         System.out.printf("The sum is %d.", sum );
       }
     }

Anonymous Classes

2009-03-04T05:18:00.000-08:00

Anonymous class is normally used to provide a simple implementation of an adapter class. Many developers don’t just wanna use these because they feel its not really required and is toocomplex.

For sure you may do the required task without using anonymous classes but sometimes it is really wise to use these. Let me list features of anonymous classes for you:

is a local class without a name
is defined and instantiated in a single expression using the new operator
anonymous class definition is an expression
it can be included as part of a larger expression (method call)

When to use it

When a local class is used only once, consider using anonymous class syntax. It places the definition and use of the class in exactly the same place.

Syntax

We use new keyword for defining an anonymous class and creating an instance of that class. It is followed by the name of a class and a class body definition in curly braces. If you wish to subclass your anonymous class, then the name following the new keyword should be the name of some superclass. This way the anonymous class is a subclass of the named class.

If you wish your subclass to implement an interface, then the name following new should be an interface. This way your anonymous class implements that interface and extends Object. Remember that the syntax does not include any way to specify extends or implements keyword.

Example

// The anonymous class is defined as part of the return statement
return new MyClass() {

public String getName() {

...

}

};
// Note the required semicolon: it terminates the return statement

Since anonymous class has no name, it is not possible to define a constructor for it within the class body. But if you provide any arguments between the parentheses following the superclass name then they are implicitly passed to the superclass constructor.

Getting warnings from JDBC Connection

2009-02-23T14:14:00.000-08:00

Sometimes it is a wise decision to retrieve the first warning reported by calls on this Connection object. This can be done using getWarnings() method. The code sample below shows how to print all the warnings with their sates and messages.

Class.forName( "sun.jdbc.odbc.JdbcOdbcDriver" ) ;
Connection conn = DriverManager.getConnection( "jdbc:odbc:Database" ) ;

// Print all warnings
for( SQLWarning warn = conn.getWarnings(); warn != null; warn = warn.getNextWarning() )
{
System.out.println( "SQL Warning:" ) ;
System.out.println( "State : " + warn.getSQLState() ) ;
System.out.println( "Message: " + warn.getMessage() ) ;
System.out.println( "Error : " + warn.getErrorCode() ) ;
}

Java Freelancing

2009-02-21T18:22:00.000-08:00

If you have good programming skills, then you may make good money doing freelancing.

Browse the follwoing

Elance
RentACoder

I may also have some work for Java gurus. Ping me for that.

mvn eclipse:eclipse

2009-02-19T14:57:00.000-08:00

mvn eclipse:eclipse is used to treat all the projects in an Eclipse workspace as Java projects.

JAR file

2008-03-03T07:02:00.000-08:00

The JAR file format is based on the popular ZIP file format, and is used for aggregating many files into one. Unlike ZIP files, JAR files are used not only for archiving and distribution, but also for deployment and encapsulation of libraries, components, and plug-ins, and are consumed directly by tools such as compilers and JVMs. Special files contained in the JAR, such as manifests and deployment descriptors, instruct tools how a particular JAR is to be treated.

A JAR file might be used:

* For distributing and using class libraries
* As building blocks for applications and extensions
* As deployment units for components, applets, or plug-ins
* For packaging auxiliary resources associated with components

Java Data Objects

2008-02-21T01:23:00.000-08:00

JDO has nothing to do with where methods are executed. JDO simply specifies how the fields of a petent object should be managed in-memory, being transparently stored to and retrieved from an underlying datastore. With JDO, methods are invoked on persistent object by an application, as per any regular in-memory Java object.

JDO has many implementations. Visit the following link to know about the available implementations.

http://db.apache.org/jdo/impls.html

valiateCharacterSetAscii

2008-02-07T02:11:00.000-08:00

The method below replaces all the non ASCII printable characters in the ArrayList provided as argument with null.

public static ArrayList valiateCharacterSetAscii(ArrayListfileContents){

ArrayList tmpList = new ArrayList();
String str = "";

for(int j=0; j < str =" fileContents.get(j);" resultantstring = "" i="0;i=33 && charCode <=126))) resultantString += str.charAt(i); else resultantString += null; } tmpList.add(resultantString); } return tmpList; }

Accessing static variables

2008-02-04T02:15:00.000-08:00

Although a static method can't access instance variables, it can access static variables. A common use of static variables is to define "constants". Examples from the Java library are Math.PI or Color.RED. They are qualified with the class name, so you know they are static. Any method, static or not, can access static variables. Instance variables can be accessed only by instance methods.

Why declare a method static

2008-02-04T01:58:00.000-08:00

Static methods can be called without using the class reference (object). Following are the two reasons, one can use static methods:

Documentation Anyone seeing that a method is static will know how to call it (see below). Similarly, any programmer looking at the code will know that a static method can't interact with instance variables, which makes reading and debugging easier.

Efficiency A compiler will usually produce slightly more efficient code because no implicit object parameter has to be passed to the method.