session bean

8/14/2019 Session Bean

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What is Session Bean?

Session is one of the EJBs and it represents a single client inside the Application Server.Stateless session is easy to develop and its efficient. As compare to entity beans sessionbeans require few server resources.

A session bean is similar to an interactive session and is not shared; it can have only oneclient, in the same way that an interactive session can have only one user. A session beanis not persistent and it is destroyed once the session terminates.

Session Bean Types

Session Beans are of two types, Stateful Session Bean and Stateless Session Bean.

Stateless Session Beans

A stateless session bean does not maintain a conversational state for the client. When aclient invokes the method of a stateless bean, the bean's instance variables may contain a

state, but only for the duration of the invocation.

Because stateless session beans can support multiple clients, they can offer betterscalability for applications that require large numbers of clients. Typically, an applicationrequires fewer stateless session beans than stateful session beans to support the samenumber of clients.

Stateful Session Beans

The state of an object consists of the values of its instance variables. In a stateful sessionbean, the instance variables represent the state of a unique client-bean session. Because

the client interacts ("talks") with its bean, this state is often called the conversationalstate.

Writing Stateful Session Bean

A Session Bean is composed of the following parts:

Remote Interface: The Remote Interface is the client view of the bean.

Home Interface: The Home Interface contains all the methods for the bean life

cycle (creation, suppression) used by the client application. Bean Class: The bean implementation class implements the business methods.

Deployment Descriptor: The deployment descriptor contains the bean

properties that can be edited at assembly or deployment time.

Steps involved in developing the Stateful Session Bean can be summarized in followingsteps:

1. Define Home Interface2. Define Remote Interface3. Develop EJB class


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4. Write deployment descriptors5. Package, deploy and test the application

Define Home Interface

The Session bean's home interface defines one or more create(...) methods and each

create method must be named create and must match one of the ejbCreate methodsdefined in the enterprise Bean class. The return type of a create method is the Bean'sremote interface type.

In case of Stateless Session Bean there is one create method with no arguments. Aremote home interface extends the javax.ejb.EJBHome interface, while a local home

interface extends the javax.ejb.EJBLocalHome interface.

Here is the source code of ourhome interface:

/*

* TestSessionBeanHome.java*/package examples;

/*** Home interface for TestSessionBean.* @author Deepak Kumar* @Web http://www.roseindia.net* @Email [email protected]*/

public interface TestSessionBeanHome extends javax.ejb.EJBHome{

public examples.TestSessionBean create() throws javax.ejb.CreateException,java.rmi.RemoteException;

}

Define Remote Interface

As mentioned earlier, Remote Interface is the client view of the bean and the functionsdefined in the remote interface is visible to the client. There should be an implementationin the Bean class for the all the functions defined in the remote interface.

Here is the source code of ourRemote Interface:

/** TestSessionBean.java**/

package examples;

/*** Remote interface for TestSessionBean.


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* @author Deepak Kumar* @Web http://www.roseindia.net* @Email [email protected]*/

public interface TestSessionBean

extends javax.ejb.EJBObject{ /** * The method that returns Hello Message */ public java.lang.String SayHello( ) throws java.rmi.RemoteException;

}

Define Enterprise Bean Class

In the EJB class we write all the business methods along with required that is necessary

to implement. In the EJB class methods are defined public. The Session Bean interfacemethods that the EJB provider must be defined in the Session bean class are:

public voidsetSessionContext(SessionContext ic);

This method is used by the container to pass a reference to the SessionContext tothe bean instance.

public voidejbRemove();

This method is invoked by the container when the instance is in the process ofbeing removed by the container.

public voidejbPassivate();

This method is invoked by the container when it wants to passivate the instance.

public voidejbActivate();This method is invoked by the container when the instance has just beenreactivated.

A stateful session Bean with container-managed transaction demarcation can optionallyalso implements the javax.ejb.SessionSynchronization interface.

The Session Synchronization interface methods that must be developed are:

public voidafterBegin();

This method notifies a session Bean instance that a new transaction has started.

public voidafterCompletion(boolean committed);This method notifies a session Bean instance that a transaction commit protocolhas completed and tells the instance whether the transaction has been committedor rolled back.

public voidbeforeCompletion();

This method notifies a session Bean instance that a transaction is about to becommitted.


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Here is the source code of ourSession Bean class:

/** SessionBean.java**/

package examples;

import java.rmi.RemoteException;import javax.ejb.CreateException;import javax.ejb.EJBException;import javax.ejb.SessionBean;import javax.ejb.SessionContext;

/*** @author Deepak Kumar* @Web http://www.roseindia.net* @Email [email protected]*/

public class MyTestSessionBean implements SessionBean{

public voidejbCreate() throws CreateException {

}

public voidsetSessionContext( SessionContext aContext ) throws EJBException {

}

public voidejbActivate() throws EJBException {

}

public voidejbPassivate() throws EJBException {

}

public voidejbRemove() throws EJBException {

}

/** * The method that returns Hello Message *

*/public String SayHello(){ String msg="Hello! I am Session Bean"; System.out.println(msg); return msg; }

}


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Writing Deployment Descriptor of Stateless Session

Bean

In this section we will write the deployment descriptor for the session bean. We need thedeployment descriptor for application (application.xml), ejb deployment descriptors (ejb-jar.xml and weblogic-ejb-jar.xml) and web.xml files.

Application Deployment descriptor:

We need the following application deployment descriptor to create our ear file(example.ear).

Stateless Session Bean Example

example.war/example

example.jar

EJB Deployment descriptor:

To create example.jar file we need ejb-jar.xml and weblogic-ejb-jar.xml files. Here is thecode forejb-jar.xml file:
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EJB ExamplesEJB Examples

Shopping Cart Session BeanShopping Cart Session Bean

ShoppingCart

examples.ShoppingCartHomeexamples.ShoppingCartexamples.ShoppingCartStatefulSessionBeanStatefulContainer

EJB Test Session BeanEJB Test Session Bean

TestSessionBean

examples.TestSessionBeanHome

examples.TestSessionBean

examples.TestSessionBeanLocalHome

examples.TestSessionBeanLocal

examples.MyTestSessionBean

Stateless

Container

testSessionBean

java.lang.String

Test Bean


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EJB Calculator Session Bean


CalculatorBean

examples.CalculatorBeanHomeexamples.CalculatorBeanexamples.CalculatorBeanLocalHomeexamples.CalculatorBeanLocalexamples.CalculatorSessionBeanStatelessContainer

CalculatorBeanjava.lang.StringCalculator bean

Session BeanSession BeanShoppingCart

*

ShoppingCart


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*Supports

The name of our session bean is TestSessionBean, we will call this bean from servlet (asdescribed in the next page).

The code for weblogic specific ejb deployment descriptor(weblogic-ejb-jar.xml) is asfollows:

Session Bean ExampleShoppingCart

ShoppingCart

TestSessionBean

TestSessionBeanTestSessionBeanLocal

CalculatorBean


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CalculatorSessionBeanCalculatorBeanLocal

The JNDI name for our Staeless Session bean is TestSessionBean. We will use this JNDIname to lookup the Bean and call it from Servlet.

Web.xml file for war file:

web.xml file describes the example.war file, which is our web application. Here is thecode of web.xml file:

sessionTest

Session Test Servletnet.roseindia.web.servlets.SessionTestServlet

1

sessionTest/SessionServlet

Note that in the above web.xml file we have define a servlet named sessionTest. We willuse this servlet to call the Staleless Session Bean. Here is the code of servlet used to callsession bean:

/** SessionTestServlet.java


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**/

package net.roseindia.web.servlets;

import javax.servlet.*;import

javax.servlet.http.*;import java.io.*;import javax.naming.*;import javax.rmi.PortableRemoteObject;

import examples.*;

/*** @author Deepak Kumar* @Web http://www.roseindia.net* @Email [email protected]* @web.servlet name="sessionTest"* display-name="Session Test Servlet"

* load-on-startup="1"* @web.servlet-mapping url-pattern="/SessionServlet"*/

public class SessionTestServlet extends HttpServlet {

TestSessionBeanHome testSessionBean;

public voidinit(ServletConfig config) throws ServletException{//Look up home interfacetry {

InitialContext ctx = new InitialContext(); Object objref = ctx.lookup("TestSessionBean"); testSessionBean = (TestSessionBeanHome)

PortableRemoteObject.narrow(objref,

TestSessionBeanHome.class);} catch (Exception NamingException) { NamingException.printStackTrace();}

}

public voiddoGet (HttpServletRequest request,HttpServletResponse response)throws ServletException, IOException{

PrintWriter out;response.setContentType("text/html");String title = "EJB Example";out = response.getWriter();


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out.println("");out.println("");out.println("Hello World Servlet!");out.println("");

out.println("");out.println("

Servlet

Calling Session Bean
");
try{TestSessionBean beanRemote;beanRemote = testSessionBean.create();out.println("

Message from

Session Bean is: " +

beanRemote.SayHello() + "
");beanRemote.remove();}catch(Exception CreateException){CreateException.printStackTrace();}
out.println("

Go to Home
");out.println("");out.println("");
out.close();}

public voiddestroy() {System.out.println("Destroy");}}

Deploying and testing Stateless Session Bean
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In this EJB tutorial we will build, deploy and test the Stateles Session Bean developed inthe last section. We will use ant build tool to build ear file. We will deploy our applicationusing WebLogic console.

Building ear file using ant build tool

I am assuming that you have ant build tool installed on your development environment.Download the source code from here and extract in your favorite directory. Opencommand prompt and navigate to the directory /sessionbean/codeand type ant there. Ant build tool will compile, package and create example.ear in the/sessionbean directory. Here is the code of our ant build file:.
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Deploying the Application on Web Logic 6.0 Server

Run the WebLogic default server:

To deploy the application we will use WebLogic console. Typehttp://localhost:7001/consoleand enter user name and password to open the WebLogicconsole.
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Navigate to "Applications" and then click on "Install a new Application", followingscreen will be displayed:


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Browse "example.ear" and then click on the Upload button. This will upload the file to

the WebLogic server directory and then install the application.


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Testing the application

To test the application open browser and type http://localhost:7001/example/index.jsp,following page should be displayed:

Click on the link "Call Session Test Servlet", it should show you the following output:
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check the WebLogic server dos console, it should be displaying the message "Hello! I amSession Bean" as show below in the screen shot:


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Writing Calculator Stateless Session Bean

In this EJB tutorial we will learn how to Write Staleles Session Bean for multiplying thevalues entered by user. We will use ant build tool to build ear file. We will deploy ourapplication using WebLogic console.

Enterprise Bean remote interface

All remote interfaces must extend javax.ejb.EJBObject. Remote interface is the clientview of session bean. Methods defined in the remote interface are accessible to the client.
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In our example we have defined thepublic int multiply(int a, int b)

method for calling from JSP. Here is code of our Remote Interface:

package examples;

/*** Remote interface for CalculatorBean.*/

public interface CalculatorBean extends javax.ejb.EJBObject{ /** * The method that returns the multiplied value */ public int multiply( int val1,int val2 ) throws java.rmi.RemoteException;

}

Enterprise Bean Home interface

All home interfaces must extend javax.ejb.EJBHome. 'create()' method of homeinterface of the application enables the client to create and remove the session object.

package examples;

/*** Home interface for CalculatorBean.*/

public interface CalculatorBeanHome extends javax.ejb.EJBHome{ public static final String COMP_NAME="java:comp/env/ejb/CalculatorBean"; public static final String JNDI_NAME="CalculatorSessionBean";

public examples.CalculatorBean create() throws javax.ejb.CreateException,java.rmi.RemoteException;

}

Enterprise Bean class

All Bean class are defined as public and implements the javax.ejb.SessionBean. In thebean class we have implemented the code for

public int multiply(int a, int b)


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Besides this method other required methods which is to be implemented are:

1. ejbCreate()2. ejbRemove()3. ejbActivate()

4. ejbPassivate()5. setSessionContext(SessionContext aContext)

Here is the code for our Calculator Session Bean:

/** SessionBean.java**/

package examples;

import java.rmi.RemoteException;import javax.ejb.CreateException;import javax.ejb.EJBException;import javax.ejb.SessionBean;import javax.ejb.SessionContext;

/*** @author Deepak Kumar* @Web http://www.roseindia.net* @Email [email protected]*/

/*** This is the Test Session Bean**/

public class CalculatorSessionBean implements SessionBean{

public voidejbCreate() throws CreateException {

}

public voidsetSessionContext( SessionContext aContext ) throws EJBException {

}

public voidejbActivate() throws EJBException {

}

public voidejbPassivate() throws EJBException {


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}

public voidejbRemove() throws EJBException {

}

/** * The method that returns the multiplied value * */public int multiply(int val1, int val2){ System.out.println("I am from multiply : " + val1 + " * " + val2); return val1*val2; }

}

Jar Descriptor File

For creating example.jarejb-jar.xml and weblogic-ejb-jar.xml files are required whichexplains the content of jar file.

ejb-jar.xml file:

EJB ExamplesEJB Examples

Shopping Cart Session BeanShopping Cart Session Bean

ShoppingCart

examples.ShoppingCartHomeexamples.ShoppingCartexamples.ShoppingCartStatefulSessionBeanStatefulContainer


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EJB Test Session BeanEJB Test Session Bean

TestSessionBean

examples.TestSessionBeanHome

examples.TestSessionBeanexamples.TestSessionBeanLocalHomeexamples.TestSessionBeanLocalexamples.MyTestSessionBeanStatelessContainer

testSessionBeanjava.lang.StringTest Bean



CalculatorBean

examples.CalculatorBeanHome

examples.CalculatorBean

examples.CalculatorBeanLocalHome

examples.CalculatorBeanLocal

examples.CalculatorSessionBean

StatelessContainer

CalculatorBean

java.lang.String

Calculator bean

Session BeanSession Bean


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ShoppingCart*

ShoppingCart*Supports

Above deployment descriptor defines remote, home and bean class for the bean andassigns a name 'CalculatorBean' to the session bean. Please note that bean of Stateless typeand is defined by:Stateless

weblogic-ejb-jar.xml file:

Session Bean Example

ShoppingCartShoppingCart

TestSessionBean

TestSessionBeanTestSessionBeanLocal

CalculatorBean


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CalculatorSessionBean

CalculatorBeanLocal

The WebLogic deployment descriptor assigns jndi name 'CalculatorSessionBean' to the'CalculatorBean' bean.

Writing JSP and Web/Ear component

Our JSP file access the session bean and uses it for the calculation and displays the result.

For this purpose we are using calculator.jsp which displays a form to accept two numbers

from the user and submits the form data to calculator.jsp. Here is our calculator.jsp:


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Calculator Bean

CalculatorCalculate *

Result =


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Web-Component Descriptor File

For creating war file we need web.xml, which is same as in previous lesson.

J2EE Enterprise Archive (ear) Descriptor File

For creating example.earapplication.xml, file is required which explains the content ofenterprise archive, which is same as in previous lesson.

Building ear file using ant build tool

I am assuming that you have ant build tool installed on your development environment.Download the source for from here and extract in your favorite directory. Opencommand prompt and navigate to the directory /sessionbean/code

and type ant there. Ant build tool will compile, package and create example.ear in the/sessionbean directory. Here is the code of our ant build file:.

Deploying the Application on Web Logic 6.0 Server

Please refer to previous lesson for deploying the application on WebLogic Server.

Testing the application

To test the application open browser and type http://localhost:7001/example/index.jsp,following page should be displayed:
https://www.vtunnel.com/index.php/1010110A/953077409dd2e2c326a8de4481e2280937951f46f8ed8eecc8e639d6403c92d59f301fac4512670f6bf1b86c627e6a4a19056https://www.vtunnel.com/index.php/1010110A/953077409dc9fad769b6d95897ff7c5a6ec40007f8e1c0ebd9fc3d9b4c3398c3c86d10ac4619056https://www.vtunnel.com/index.php/1010110A/953077409dd2e2c326a8de4481e2280937951f46f8ed8eecc8e639d6403c92d59f301fac4512670f6bf1b86c627e6a4a19056https://www.vtunnel.com/index.php/1010110A/953077409dc9fad769b6d95897ff7c5a6ec40007f8e1c0ebd9fc3d9b4c3398c3c86d10ac4619056


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Click on the link "Calculator Links", it should display the form to enter the two values:

Click on the Calculate button to view the result. Following should be displayed:


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Understanding Stateful and Stateless Session Bean Life

Cycle

In this section of EJB tutorial, we will learn about the lifecycle of Stateful and StatelessSession Beans.

Stateless Session Bean Life cycle

There are two stages in the Lifecycle of Stateless Session Bean. These are:

a) Does Not Exist

In the Does Not Exist stage, bean does not have instance in the memory. In this stagebean has not been instantiated.

b) Method Ready PoolIn the Method Ready Pool stage bean has instance(s) in the memory of the EJB containerand it is ready to serve clients. On the startup of the EJB container some instances of thebean are created and placed in the pool. EJB container creates the new instance of theBean and then sets the session context (setSessioncontext()) and it calls the ejbCreate()
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method to place the bean in the Method Ready Pool stage. Container calls theejbRemove() method to move the bean into Does Not Exist state.

Following Diagram shows the Life cycle of Stateless Session Bean

Stateful Session Bean Life cycle

There are there stages in the life cycle of Stateful Session bean Life cycle. These are:

a) Does Not ExistThis is the Does Not Exist stage, bean does not have instance in the memory. In this stagebean has not been instantiated.

b) Method Ready PoolIn the Method Ready Pool stage bean has instance in the memory of the EJB containerand it is ready to serve client. One instance of the Stateful Session Bean servers only oneclient. When Client Calls create(args) method on the Home Interface, server creates newinstance of the bean and sets the Session Context and then container calls theejbCreate(args) method on the bean and places the bean into Method Ready Pool stage.ejbRemove or Timeout moves the bean into Does Not Exist stage.

c) Passive stateIn the Passive state the bean is passivated to conserve the resource. The passivate methodis called before the instance enters the "passive" state. The instance should release any

resources that it can re-acquire later in the ejbActivate() method. After the passivatemethod completes, the instance must be in a state that allows the container to use the JavaSerialization protocol to externalize and store away the instance's state. ejbRemove orTimeout moves the bean into Does Not Exist stage.

Following Diagram shows the Life cycle of Statelful Session Bean


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session bean

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