JavaBeat Tips

Use a4j:status to display status of the request

When there is a request to the server, the client have to wait untill he gets the response. It will be nice if you give status of the server request processing. use a4j:status tag in the RichFaces to implement this feature in your webpages. In this example this tag is used with a4j:support and showing the status message while user types in the text field.

a4j:support - How to use action attribute?

This example program demonstrates how to use action attribute to update the server values and display in the screen. In this example user inputs are passed to update method and processed. The values are updated in the h:panelGrid component. The advantage of using a4j:support tag is it can be updated the whole region by specifying the reRender attribute.

a4j:support - Simple Example on onkeyup event

This example program demonstrates how to get started with a4j:support tag in the RiachFaces tag libraray. This is part of Ajax4jsf libraray. But, from RiachFaces 3.0, Ajax4jsf is merged with RichFaces tag libraray. a4j:support is used inside any component to provide ajax support on that particular field.

How to write Throws Advice in Spring AOP?

Throws Advice is used when throwing exception from the business methods. This interceptor will be called when there is any exception, so one can do any logic to candle the exception.

How to write Interception Around Advice in Spring AOP?

In this tips we explore how to use the Interception Around Advice in Spring's Aspect Oriented Programming(AOP). Interception Around Advice is fundamental advice type in the Spring framework. Also this advice type is derived from other frameworks like AspectJ. So it is interoporable with other framework, other advices in the Spring AOPs are specific to Spring Framework and cannot be used in the other similar frameworks.

Simple example for Before advice and After Advice in Spring Framework

This tips presents a very simple program for invoking the Before Advice and After Advice in the Spring Framework. Thsese two methods are part of Spring's AOP implementation and used as interceptor methods.

Editing eclipse classpath file

While creating a project in Eclipse, by default it creates a .classpath file in the project directory. That file will be usedfor storing file names and other dependent files needed in the classpath to compile and execute the project successfully.

Baisc steps to configure Log4j using xml and properties file

This example demonstrated how to configure Log4j setup using the Proerties file and XML file. These are the two most widely used techniques for configuring the Log4j for your application. But, in the recent days configuring with properties files are considered to be old technique and recommended using XML.

Batch insert in Hibernate

This example program shows how to insert multiple rows using the batch processing in hibernate. when there are thousand of rows to be persisted, everytime iterating and inserting will cause the memory problem. Hibernate stored all the persisted objects in the memory. To avoid this problem use batch processing in the hibernate.

Hibernate basic configuration example

This example demonstrates how to configure hibernate framework for running a simple standalone program. Here the sample program uses programmatic configuration to set all the properties required for running hibernate. Also the example uses derby as the database to connect and update the values. This is not the big change, you only have to change few parameters if you are using any other databases.

Accessing Managed Bean methods programmatically in JSF 1.1

As we know JSF managed beans are mostly access only through the JSP pages are faces-config.xml. But, there is some schenarios where you will need information stored in the managed beans for the business logic in some other beans. JSF provides API to access those values where ever you want.

How to use Managed Bean reference inside faces-config.xml?

Managed Bean in JSF can refer another managed bean inside the faces-config.xml. There is no restriction for the type of bean can be refered. But, JSF does not support the cyclic dependencies for Managed Bean reference. For example, you cannot refer bean B from bean A while bean B also refers to bean A. The following simple program demonstrates how to refer a listBean inside a normal JSF Managed Bean. For simplicity purpose this example use List as managed bean. You can use any type of bean for the reference.

How to initialize Map property in Managed Mean?

JSF Managed Beans can initialize its Map properties in the faces-config.xml. There is a property in the faces-config.xml as map-entries. This cane be used for initializing the values and can be accessed directly through the Managed Beans in any JSP pages.

How to initialize List property in Managed Mean?

JSF Managed Beans can initialize its List properties in the faces-config.xml. There is a property in the faces-config.xml as list-entries. This cane be used for initializing the values and can be accessed directly through the Managed Beans in any JSP pages.

Lists and Maps as Managed Beans in JSF

This tips explain how to use List and Map classes directly as Managed Beans. Here notice that you cannot use List and Map interfaces directly as Managed Beans, you can use only the implementations classes like ArrayList, Map,etc. There is no way to call constructor in the interfaces if you use List or Map directly.

Publish and Subscribe messages using JMS Topic in JBoss Server

This tips gives overview on how to write Java Messaging Service(JMS) code for creating Topic in the Tomcat server. This is very basic example and only show how to get started instead of looking into the advanced concepts in JMS technology.

How to use h:selectOneRadio inside h:dataTable in JSF?

This tips explains how to use the h:selectOneRadio tag inside h:dataTable iteration tag. Using h:selectOneRadio is not straight forward since JSF dowsn't provide easy mechanism for toggling the radio button selectios. Programmer has to write the manual script code to toggle the radio selections.

Write your own Validator in JSF

This tips presents sample programs for how to write the custom validator in JSF application. There is many built-in validators available in JSF.

Create simple custom Converter implementation class in JSF

This article explains the simple Converter class implementation. Converter class is used for converting any given input to the desired output format or with any business logic to the input values. This example also includes the PhaseListener to identify in which JSF lifecycle phase the convertion happens.

How to implement f:phaseListener for h:commandButton?

How to implement f:phaseListener for h:commandButton? - PhaseListener in JSF

How to read xml file and inject bean reference using Spring Framework?

This article presents sample source code for creating the Bean instance using the Spring Framework. This is basic example to read configuration file from the file system and create the beans from the applicationContext.xml file. This xml file define two beans Employee and Address.

How to implement ActionListener (f:actionListener) in JSF?

This article explains how to implement the ActionListener class in the JSF core tag library. An ActionListener is an event handler interface for a class that can respond to user events in your JSF page. The body content of this tag must be empty.

f:convertDateTime tag in JSF

f:convertDateTime is used for validating the date input. If the user enters any invlid input, it will throw the error message to the screen. Also it allows the user to specify the apttern of date format using the 'pattern' attribute.

h:outputFormat tag in JSF

The outputFormat tag renders parameterized text and allows you to customize the appearance of this text using CSS styles. Parameterized text is compound text containing placeholder values to be replaced by actual values at rendering time.

f:convertNumber Tag in JSF

This tag is used to register the NumberConverter instance on the enclosing component. This class is responsible to convert String to java.util.Number object and vice-versa.

Create EJB 3.0 project in NetBeans 6.1

This article explains how to create EJB 3.0 project using NetBeans IDE 6.1. This article will not explain the details of EJB 3.0 but will give basic knowledge on how to create simple EJB 3.0 project using NetBeans 6.1 IDE.

Entity Beans in EJB(BMP)

Thus far, we acquainted ourselves with Sessionbeans ( both stateless and stateful) and also CMP Entity bean. In this instalment, we take up the most difficult type, (ie) Bean-Managed Persistent Entity bean.(BMP)

Entity Beans in EJB(CMP)

As already mentioned ,Entity beans can be thought of as a record ( or row) in a table of a relational database. ( This is just for easy understanding because, the database can also be Object Database, XML database etc.)

Java Security Packages using JCA/JCE

In this tutorial, the author explains the cryptography-related concepts and packages in JDK,with code examples.Many of the concepts and technical terms thus learnt will be useful in understanding the Cryptography API in MFC also.

Java Messaging Service(JMS)

A brief note and demo for JMS ( Java Messaging Service)

JSTL and SQL-TAGS

In this fourth and last part of the tutorial on JSTL,the author deals with the 'sql' tags in JSTL and shows how they greatly simplify simple database operations like 'select' queries. In another demo, common database operations like 'add','modify' , 'delete' and 'verify'also are dealt with.

JSTL and XML-TAGS

In this third part of the tutorial on JSTL, the author explains the use of xml tags of the JSTL and shows their wonderful simplicity ,ease of use and raw power.

Core Tags in JSTL

In the second part of this tutorial on JSTL, the author explains how the tags in the core-group can be used in JSP pages, with a number of simple examples.

An Introduction to JSTL

As J2EE programmers, we are familiar with Servlets , JSP and JavaBeans. Any JSP page should encapsulate the business logic in a bean and invoke it by using jsp:useBean tag. Till recently, a combination of Servlets, JSP and beans was the standard practice. But, the JCP realeased an API for enabling programmers to create custom tags and use them in their JSP pages. The difference between javabean and java custom tags was that, though both made use of java classes, tags can be used by non-programmers also without knowledge of Java programming, just as they would use html tags.( From a programmers perspective,however, a much more important distinction is that tags are specific to the page in which they are created while javabeans are general. )

Getting Started with Flex 2.0

Flex2 is the latest RIA technolgy based on MXML and Flash.Originally from Macromedia, this software is now being provided by Adobe, as Adobe has recently acquired Macromedia. The Flex2 software was given in DeveloperIQ CD in August-2006. That edition carried a very interesting and informative interview with Dave Gruber of Adobe by the editor Mr.Ramdas. Flex2 is being positioned and promoted as a better technology than Ajax. ( this is the impression that we gain, from their advertisements in JavaLobby site). The aim of this introductory tutorial is to explore the technology at a very basic level. However, what we see by these basic experiments is that it is just like DotNet Framework and ASP.net , atleast so far as naming of controls etc are concerned and partly like an applet( it is executed in client-side).

What is Spring?

Spring is grate framework for development of Enterprise grade applications. Spring is a light-weight framework for the development of enterprise-ready applications. Spring can be used to configure declarative transaction management, remote access to your logic using RMI or web services, mailing facilities and various options in persisting your data to a database. Spring framework can be used in modular fashion, it allows to use in parts and leave the other components which is not required by the application.

Display error messages in JSF [ h:messages ] - part 1

h:selectOneMenu - Java Server Faces (JSF)

h:selectManyMenu - Java Server Faces (JSF)

h:selectManyCheckBox - Java Server Faces (JSF)

h:selectBooleanCheckBox - Java Server Faces (JSF)

How to use Resource Bundle in JSF?

h:dataTable - Java Server Faces (JSF)

How to set selected tab in rich:tabPanel tag?

h:commandLink - How to pass Parameter to next page?

How to use h:selectBooleanCheckBox within h:dataTable?

f:attribute Tag in Java Server Faces (JSF)

Display error messages in JSF [ h:message ] - part 2

Display error messages in JSF [ h:messages ] - part 1

Knowing about your Database

We use the Jdbc APIs for accessing the data from the database system. However, the different databases from different vendors will vary a lot in their underlying model and functionalities. For example, a feature supported in one database might not be supported in another database. So, even before working with a database, it is important to know the supported features and other related information. Java provides an interface called DatabaseMetaData to achieve this.

Customizing Dragging and Dropping for Swing Components

Swing's Drop and Drop API can be used for customizing Drag and Drop support. For most of the commonly used components like Text Components, Color Chooser, File Chooser etc, the dropping support is enabled by default. We have to explicitly enable the dragging support by calling the setDragEnabled() method. Before getting into customizing them, let us see a simple example,

Locking Files using Java

File Locking can be achieved in java by making use of the New I/O API (nio). Before the advent of New I/O API, there was no direct support in Java for locking a file. It is important to understand that File locking is hugely dependent on the native operating system on which the program is executing.

File Upload and Download using Java

File Upload and Download is always a handy utility to know. There will be some need to upload a file to an FTP server, Like if you generate a report or store some data in .xls file, then it needs to be uploaded to a FTP server for further use. like wise we need to download some data (data stored in .xls files)for manuplation from the server in our projects. Here we have the code to do this for us. The FileUploadDownload utility.

Precise rounding of decimals using Rounding Mode Enumeration

The Rounding Mode Enum in java.math package is used to perform precise rounding of decimal values. It was introduced in Java 5.0. This Enum provides various constants each of which is used for different modes of rounding. The decimal value would be rounded off to the number of decimal places based on the scale that is defined for the decimal value.

Using the Prototype pattern to clone objects

Prototype pattern is one of the creational patterns that concentrate on duplicating objects if needed. Assuming that we are in process of creating a template. Most of the times, we copy an existing template, do some changes in it and then will use it.

Sending mail from Java

The Java Mail API provides support for sending and receiving electronic mail messages. The API provides a plug-in architecture where vendor's implementation for their own proprietary protocols can be dynamically discovered and used at the run time. Sun provides a reference implementation and its supports the following protocols namely,

Passing arguments and properties from command line

Arguments and properties can be passed to a java application from command line. In this techical tip, let us see how to pass arguments as well as properties from command line.

Generation of Random Numbers

Random numbers in java can be generated either by using the Random class in java.util package or by using the random() method in the Math class in java.lang package.

Downloading Content from the Internet

Let us write a Simple Downloader in this techincal tip by making use of the classes with java.net package. URL stands for Uniform Resource Locator and it is used to locate a resource in the Web in a standard fashion. A resource in the Web can be anything;

Creating user defined exceptions

Though Java provides an extensive set of in-built exceptions, there are cases in which we may need to define our own exceptions in order to handle the various application specific errors that we might encounter.

Copying File Contents using FileChannel

In this technical tip, let us see an easy way of achieving file copy using File Channels. File Channels are part of Java New I/O Packages. A file can be viewed as a sequence of bytes. The various Buffer classes in New I/O Packages serve as a container for manipulating the primitive byte contents.

Logging Messages using Java Logging API

The Logging API in Java enables Applications to log messages of some level which will be very useful for debugging purpose. Say, if a system fails for some reasons, then the reason can be easily traced out by looking at the information available in the log file. In this section, let us see an overview of using Logging facility in Java.

Working with Virtual Proxy Pattern

Application is often a collection of components and in most of the situations it may be the case that a component should be loaded until it is first accessed by the Client. Reasons may be that the component in consideration may be using most of the system resources. For example,

Making use of the Properties class

In this section, let us make use of the Properties class for storing and loading application related configuration values as well as other user information. It is also possible to query or modify the various System properties using this class. For example, the following code tries to get all the properties that are available for the currently executing JVM.

Parsing Input using Scanner

A Scanner object can be used to read text input from a number of sources. The input source can be a file, an input stream or even from a string. It internally uses the Regular Expression Api for parsing and getting the input. Let us see a simple example to parse a String object,

Parsing XML Documents using SAX

Xml Parsers are used to parse and extract information from Xml Documents. The most commonly used Xml Parsers are Simple API for Xml Parsing and Document Object Model. SAX Parsers are preferred when the size of the Xml Document is comparatively large and the application doesn't wish to store and reuse the Xml information in the future. In this tip, let us see how to parse an Xml Document using SAX Technique.

Persisting Object State in Xml Format

Persistence is the process of saving the state of an object permanently to a storage like file or database, and the state of the object can be restored at a later time. In Java terms, Persistence is nothing but Serialization. For example, the following code is used to save the state of an object in a file.

Randomly accessing the file contents

In this techincal tip, let us see how to access the contents of a file randomly instead of the traditional sequential access. Imagine that we want to search for a particular record in a file. If we prefer Sequential access in this case, then it will involve traversing over the file byte by byte and searching for the relevant record. This won't be an ideal solution particularly if the size of the file is too big.

Sorting Custom Types in Java

The class java.util.Collections provides many Utility methods for simplifying the most commonly used operations. One of the methods available in that class is sort() which is used for sorting elements. Let us the see how the Collections.sort() method operates on pre-defined data-types as well as user-defined data-types.

Recursively traversing files and folders using Java File API

In this section, let us see how to recursively traverse over files and folders by making use of Java File API. Whether it is a folder or a file, both are represented as a java.io.File object. For example, consider the following code snippet,

Factory pattern - Design Patterns in Java/J2EE

Creational pattern deals with the creation of objects and it hides the complex logic involved in the object creation object from the clients. One of the common creational patterns is the Factory pattern and it is used extensively in Applications. Let us understand what factors should be considered in mind while designing a Factory pattern or a Factory method pattern.

Conversion between Array and List types

In some cases, we may need to convert an array to a list or vice versa. The method asList() is available in the Arrays class, and the toArray() method in list and set classes serve this purpose.

Querying Class Information at Runtime using Java Reflection API

Java Reflection API provides support for querying information about a class at run-time. This information includes the list of public as well as private members (methods) available for the class, the various public operations it supports etc. This section will guide you in making use of the Reflection API.

Using the Jar Utility

Jar stands for Java Archive file and it is used to compress and archive one or more files. It is equivalent to Zip file in Window operating system. A typical jar file contains Java class files in addition to source files as well as resource files, like images and properties.

Storing Application Data using Preferences API

Applications can now make use of the Java Preferences API for storing and retrieving Application related data. The location where the Data gets stored is implementation specific. Two levels of Preferences come into picture, one is the User Preferences for storing user information and the other is the System Preferences that deals with information common to all users as well as configuration details.

Threads Synchronization

Synchronization is done in order to protect a segment of code from being accessed by more than a single Thread at any particular instance of time. In Java, synchronization is achieved with the use of synchronized keyword. Synchronization can be applied to methods as well as to a block of code.

Overriding the toString() method in Object class

The toString() method in the Object class is used to display some information regarding any object. If any code needs some information of an object of a class, then it can get it by using this method

Using the Externalizable Interface

Serialization is the process of giving persistence storage to Java objects so that they can be restored at a later time. Classes can be made persistent in Java by implementing the Serializable interface. Serializable is a marker interface meaning that it has no methods within it. Any Serializable class can be passed on to ObjectOutputStream.writeObject(object) for saving the object state and a call back to ObjectInputStream.readObject() will get the object back from the storage.

Enhanced for-loop for User-defined objects

Enhanced For-loop is a new syntax for traversing over a collection of objects and it was introduced from Java 5.0. Let us see how Enhanced for-loop operates on user-defined Objects. The following example shows the syntax of using enhanced for-loop on a Collection object,

HashCode and equals methods

HashTable, HashMap and HashSet are the Collection classes in java.util package that make use of hashing algorithm to store objects. In all these Collection classes except HashSet, objects are stored as key-value pairs. For the storage and the retrieval of any user-defined objects it is a good practice to override the following methods which is mentioned below,

Using the new Process Builder class

We all know how to execute programs from within a Java Application by making use of the Runtime Api. For example, assume that we want to launch the Internet Explorer browser within the Java code. Then the following code snippet will just do that,

Singleton Pattern - Design Patterns in Java/J2EE

Situations often will demand for the existence of only one object for a particular class in an Application. For example, the existence of only one Database Connection for a particular session, one object referencing the set of Global properties being shared across the various modules, etc.

Template method Pattern - Design Patterns in Java/J2EE

A Template method pattern provides a skeleton for performing any sort of algorithm or an operation, and it allows the sub-classes to re-define part of the logic. Let us directly get into an example to clarify things in a much better manner. For example, if we wish to write a String Decorator class,

State Pattern - Design Patterns in Java/J2EE

State pattern falls under the category of Behavioural patterns. Assume that we have an object and its behavior is largely dependent on the state of its internal variables. Consider the following example,

Expression Language in JSP 2.0

Expression Language was first introduced in JSTL 1.0 (JSP Standard Tag Library ). Before the introduction of JSTL, scriptlets were used to manipulate application data.JSTL introduced the concept of an expression language (EL) which simplified the page development by providing standerd tag libraries. These tag libraries provide support for common, structural tasks, such as: iteration and conditionals, processing XML documents, internationalization and database access using the Structured Query Language (SQL). The Expression Language introduced in JSTL 1.0 is now incorporated in JavaServer Pages specification(JSP 2.0). This articie gives some idea about what is Expression Language and how to simplify the maintenance for JSP applications by avoiding scripting elements.