( PUBLISHED IN DEVELOPERIQ

http:://in.geocities.com/rsramsam/linker.htm

Invoking an EntityBean

by using a SessionBean

( Façade Pattern)

R.S.RAMASWAMY

(rsramsam@yahoo.co.in)

( PUBLISHED IN DEVELOPERIQ.....DECEMBER-2003)

( in continuation of Entity beans..BMP).

======================================================================================

So far, in all our examples, the client program for invoking the EJBean has either been a console mode program or a servlet.Sometimes, it will be a better method if we make a SessionBean invoke other beans in the EJB server. This will reduce network traffic to a great extent.

In this case, the end user sends data to the servlet, the servlet invokes a session bean and the session bean invokes the session and entity beans in the EJB server. As both the invoking and invoked EJB's are available within the EJB server itself, it speeds up things and reduces repeated calls over the network, thereby resulting in quicker response.

In our example, we will however use a console-mode client

to invoke a stateless sessionbean which in-turn invokes a CMP.

Let us call our stateless sessionbean in this demo 'linker',as we use it to link with the CMP bean already in the EJB server.

Please review the CMPBean code already dealt with. In that demo, the client was a console mode program.This console mode client located the CMPBean by the following code fragment:

----------------------------------------------------

Properties props = new Properties();

props.put(Context.INITIAL_CONTEXT_FACTORY,

"weblogic.jndi.WLInitialContextFactory");

props.put(Context.PROVIDER_URL,

"t3://127.0.0.1:7001" );

Context context = new InitialContext(props);

customerHome home= (customerHome) context.lookup

("customerJndi");

-------------------------------------------------

We will be using the same code to invoke the customerHome

by using 'linker' session bean. This can be seen from the code

given for 'linkerBean', below.

Apart from this , there is no difference. However, we will have to modify the ejb-jar.xml file as well as weblogic-ejb-jar.xml files,suitably as shown, to reflect the fact that there is reference to ejb from another ejb.

-------------------------------------------------------------

//************** linkerRemote.java *********************

import javax.ejb.*;

import java.rmi.*;

public interface linkerRemote extends EJBObject

{

public String getdata(String s) throws RemoteException;

}

-------------------------------------------------------------

// ***************** linkerHome.java ******************

import javax.ejb.*;

import java.rmi.*;

public interface linkerHome extends EJBHome

{

public linkerRemote create() throws RemoteException, CreateException;

}

---------------------------------------------------------

//*************** linkerBean.java **********************

import javax.ejb.*;

import javax.naming.*;

import customerRemote;

import customerHome;

import java.util.*;

public class linkerBean implements SessionBean

{

public void ejbCreate() { }

public void ejbRemove() { }

public void ejbActivate() { }

public void ejbPassivate() { }

public void setSessionContext(SessionContext context) { }

//=============================================

public String getdata(String s)

{

String s3="";

try

{

Properties props = new Properties();

props.put(Context.INITIAL_CONTEXT_FACTORY,

"weblogic.jndi.WLInitialContextFactory");

props.put(Context.PROVIDER_URL,

"t3://127.0.0.1:7001");

Context context = new InitialContext(props);

customerHome home =

(customerHome) context.lookup("customerJndi");

customerRemote remote=home.findByPrimaryKey(s);

String s1 = remote.getName();

String s2 = remote.getPlace();

s3=s1+"......."+s2;

}catch(Exception e1){System.out.println(""+e1);}

return s3;

}

=======================================================================

We now create the required xml files. Pay particular attention to

the ejb-ref section in ejb-jar.xml file! This is how we link with the CMPBean.

Similarly, note the section 'referencedescriptor ' in weblogic-ejb-jar.xml file.

// ****************** ejb-jar.xml ***************

-------------------------------------------------

<?xml version="1.0" ?>

<!DOCTYPE ejb-jar PUBLIC

"-//Sun Microsystems, Inc.//DTD Enterprise JavaBeans 1.1//EN"

"http://java.sun.com/dtd/ejb-jar_1_1.dtd">

<ejb-jar>

<enterprise-beans>

<ejb-name>linkerBean</ejb-name>

<home>linkerHome</home>

<remote>linkerRemote</remote>

<ejb-class>linkerBean</ejb-class>

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

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

<ejb-ref>

<ejb-ref-name>customerJndi</ejb-ref-name>

<ejb-ref-type>Entity</ejb-ref-type>

<home>customerHome</home>

<remote>customerRemote</remote>

<ejb-link></ejb-link>

</ejb-ref>

</session>

</enterprise-beans>

</ejb-jar>

======================================================================

weblogic-ejb-jar.xml

===================

<?xml version="1.0" ?>

<!DOCTYPE weblogic-ejb-jar PUBLIC

'-//BEA Systems, Inc.//DTD WebLogic 5.1.0 EJB//EN'

'http://www.bea.com.servers/wls510/dtd/weblogic-ejb-jar.dtd'>

<weblogic-ejb-jar>

<weblogic-enterprise-bean>

<ejb-name>linkerBean</ejb-name>

<reference-descriptor>

<ejb-reference-description>

<ejb-ref-name>customerJndi</ejb-ref-name>

<jndi-name>customerJndi</jndi-name>

</ejb-reference-description>

</reference-descriptor>

<jndi-name>linkerJndi</jndi-name>

</weblogic-enterprise-bean>

</weblogic-ejb-jar>

--------------------------------------------------------------------

Finally, we have to modify the weblogic.properties file as follows:

# # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #

# WEBLOGIC EJB DEMO PROPERTIES

# --------------------------------------------------

weblogic.ejb.deploy=\

c:/weblogic/beans/cmp/customer1.jar,\

c:/weblogic/beans/linker/linker1.jar

-------------------------------------------------------

WEBLOGIC DEMO CONNECTION POOL PROPERTIES

# --------------------------------------------------

weblogic.jdbc.connectionPool.demoPool=\

# url=jdbc:cloudscape:demo,\

url=jdbc:odbc:customer,\

# driver=COM.cloudscape.core.JDBCDriver,\

driver=sun.jdbc.odbc.JdbcOdbcDriver,\

initialCapacity=3,\

maxCapacity=5,\

capacityIncrement=3,\

props=user=none;password=none;server=none

# Add a TXDataSource for the connection pool:

# weblogic.jdbc.TXDataSource.weblogic.jdbc.jts.demoPool=demoPool

weblogic.jdbc.TXDataSource.customer=demoPool

# Add an ACL for the connection pool:

weblogic.allow.reserve.weblogic.jdbc.connectionPool.demoPool=everyone

-------------------------------------------------------------------

The procedure for compiling the source files, creating the jar file and deploying the jar file in weblogic server is the same as before.

-------------------------------------------

After successfully deploying the two EJ-beans, ( check up that you get the message that customerBean and linkerBean have been deployed). we create the following client file .

// *************** linkerClient.java *********************

import javax.ejb.*;

import java.rmi.*;

import javax.rmi.*;

import javax.naming.*;

import java.util.*;

import linkerRemote;

import linkerHome;

import java.io.*;

public class linkerClient

{

public static void main(String args[])

{

try

{

Properties props = new Properties();

props.put(Context.INITIAL_CONTEXT_FACTORY,

"weblogic.jndi.WLInitialContextFactory");

props.put(Context.PROVIDER_URL,

"t3://127.0.0.1:7001");

System.out.println("please wait: contacting remote server!");

Context ctx = new InitialContext(props);

linkerHome home = (linkerHome)ctx.lookup("linkerJndi");

linkerRemote remote = home.create();

String a = remote.getdata(args[0]);

System.out.println(a);

} catch(Exception e1) { System.out.println(" " + e1); }

} // main

}// class

//******************************************************************

We compile this file and then run the program.

>java linkerClient 543

( We have already created a record "543","SAM", "MADRAS")

So, we get the response as :

SAM......MADRAS

That completes the lesson on invoking an EntityBean using a SessionBean.

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