Sample EJB

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Hello World applicationwith EJB

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Hello World application

z Simple server that prints the string “Hello, world !”

z Implemented using a stateless session bean

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Steps to be followed

1. Component development * Describe Remote interface * Describe Home interface * Implement the Bean class

2. Write deployment descriptor(s)

3. Package in an archive (jar file) all EJB files

4. Deployment into the container

5. Implement the client application

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Remote interface : HelloWorld.java

z Corresponds to the interface descriptionz Gives the list of the methods the client can call

import java.rmi.*;

import javax.ejb.*;

public interface HelloWorld extends EJBObject {

public String sayHello() throws RemoteException;

}

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Home interface : HelloWorldHome.java

z Provides methods for the client to create, find or remove an EJB.z To use an EJB, a client must first get a reference to its Home

interface using JNDI (Java Naming and Directory Interface).z The create() method returns a reference to the EJB remote

interface (HelloWorld).

import java.rmi.RemoteException;

import java.ejb.CreateException;

import javax.ejb.EJBHome ;

public interface HelloWorldHome extends EJBHome {

public HelloWorld create() throwsCreateException, RemoteException;

}

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Bean implementation class :HelloWorldBean.java

import javax.ejb.SessionBean;

import javax.ejb.SessionContext;

public class HelloWorldBean implements SessionBean {

// Methods of Remote interface

public String sayHello() {

return "Hello, world !";

}

// Methods of Home interface

public void ejbCreate() {}

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Bean implementation class :HelloBean.java (cont.)

// Methods of SessionBean interface

protected SessionContext ctx;

public void setSessionContext(SessionContext ctx) {

this.ctx = ctx;

}

public void ejbRemove() {}

public void ejbActivate() {}

public void ejbPassivate() {}

}

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Deployment Descriptor : ejb-jar.xml<ejb-jar>

<description>HelloWorld deployment descriptor</description>

<display-name>HelloWorld</display-name>

<enterprise-beans>

<session>

<description> HelloWorld deployment descriptor </description>

<display-name>HelloWorld</display-name>

<ejb-name>HelloWorld</ejb-name>

<home>HelloWorldHome</home>

<remote>HelloWorld</remote>

<ejb-class>HelloWorldBean</ejb-class>

<session-type>Stateless</session-type>

<transaction-type>Container</transaction-type>

</session>

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Deployment Descriptor : ejb-jar.xml (cont.)

</enterprise-beans>

<assembly-descriptor>

<container-transaction>

<method>


<method-name>*</method-name>

</method>

<trans-attribute>Required</trans-attribute>

</container-transaction>

</assembly-descriptor>

</ejb-jar>

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Additional Deployment Descriptor(specific to Jonas) : jonas-ejb-jar.xml

<jonas-ejb-jar>

<jonas-session>


<jndi-name>myHelloWorld</jndi-name>

</jonas-session>

</jonas-ejb-jar>

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Packaging and deploying the EJB

z An EJB must be packaged in a “.jar” file containing

ª Class files

ª Deployment descriptors

z In order to be used, an EJB must first be deployed

ª Copy the jar file in a specific directory for the container to get it from

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Client : HelloClient.java

import java.util.Properties;

import javax.naming.InitialContext;

import javax.naming.Context;

import javax.transaction.UserTransaction;

import javax.rmi.PortableRemoteObject;

public class HelloClient {

public static void main(String args[]) {

...

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Client : HelloClient.java (cont.)try {

Context initialContext = new InitialContext();

Object objref = initialContext.lookup("myHelloWorld");

HelloWorldHome home =(HelloWorldHome)PortableRemoteObject.narrow(objref,HelloWorldHome.class);

HelloWorld myHelloWorld = home.create();

String message = myHelloWorld.sayHello();

System.out.println(message);

} catch (Exception e) {

System.err.println(" Erreur : " + e);

System.exit(2);

}

}

}

Documents

Sample EJB