Exercise 4.2: A Simple Session Bean

In this exercise, you will create and build the TravelAgent EJB. This simple bean illustrates the use of a stateless session bean and mirrors the code shown in Chapter 4 of the EJB section of this book.

Start Up JBoss

If you already have JBoss running, there is no reason to restart it. Otherwise, start it up as instructed in the JBoss Installation and Configuration chapter.

Initialize the Database

The database should contain the 100 rows created by a successful execution of the test programs from the previous exercise, Client_1 and Client_2.

Build and Deploy the Example Programs

Perform the following steps:

  1. Open a command prompt or shell terminal and change to the ex04_2 directory created by the extraction process.

  2. Set the JAVA_HOME and JBOSS_HOME environment variables to point to where your JDK and JBoss 4.0 are installed. Examples:

    Windows: C:workbookex04_2> set JAVA_HOME=C:jdk1.4.2 C:workbookex04_2> set JBOSS_HOME=C:jboss-4.0
    Unix: $ export JAVA_HOME=/usr/local/jdk1.4.2 $ export JBOSS_HOME=/usr/local/jboss-4.0

  3. Add ant to your execution path. Ant is the build utility.

    Windows: C:workbookex04_2> set PATH=..antin;%PATH%
    Unix: $ export PATH=../ant/bin:$PATH

  4. Perform the build by typing ant.

As in the last exercise, you will see titan.jar rebuilt, copied to the JBoss deploy directory, and redeployed by the application server.

Examine the JBoss-Specific Files

In this example, the jboss.xml deployment descriptor overrides the default JNDI binding for the deployed EJBs. CabinEJB is bound to CabinHomeRemote and TravelAgentEJB is bound to TravelAgentHomeRemote.

jboss.xml

<jboss>
  <enterprise-beans>
    <entity>
      <ejb-name>CabinEJB</ejb-name>
      <jndi-name>CabinHomeRemote</jndi-name>
    </entity>
    <session>
      <ejb-name>TravelAgentEJB</ejb-name>
      <jndi-name>TravelAgentHomeRemote</jndi-name>
      <ejb-ref>
        <ejb-ref-name>ejb/CabinHomeRemote</ejb-ref-name>
        <jndi-name>CabinHomeRemote</jndi-name>
      </ejb-ref>
    </session>
  </enterprise-beans>
</jboss>

The EJB book describes how you must use <ejb-ref> declarations when one EJB references another. The TravelAgent EJB references the Cabin entity bean, so the following XML is required in ejb-jar.xml.

ejb-jar.xml

<ejb-ref>
  <ejb-ref-name>ejb/CabinHomeRemote</ejb-ref-name>  
  <ejb-ref-type>Entity</ejb-ref-type>
  <home>com.titan.cabin.CabinHomeRemote</home>
  <remote>com.titan.cabin.CabinRemote</remote>
</ejb-ref>

If you have a <ejb-ref-name> declared in your ejb-jar.xml file, you must have a corresponding <ejb-ref> declaration in your jboss.xml file that maps the portable JNDI name used by the TravelAgent EJB to the real JNDI name of the Cabin EJB.

jboss.xml

<jboss>
  <enterprise-beans>
    <entity>
      <ejb-name>CabinEJB</ejb-name>
      <jndi-name>CabinHomeRemote</jndi-name>
    </entity>
    <session>
      <ejb-name>TravelAgentEJB</ejb-name>
      <jndi-name>TravelAgentHomeRemote</jndi-name>
      <ejb-ref>
       <ejb-ref-name>ejb/CabinHomeRemote</ejb-ref-name>
       <jndi-name>CabinHomeRemote</jndi-name>
      </ejb-ref>
    </session>
  </enterprise-beans>
</jboss>

Examine and Run the Client Application

The example program in this section invokes the TravelAgent EJB to list cabins that meet certain criteria.

Client_3.java

...
Context jndiContext = getInitialContext( );           

Object ref = jndiContext.lookup("TravelAgentHomeRemote");               
TravelAgentHomeRemote home = (TravelAgentHomeRemote) 
   PortableRemoteObject.narrow(ref,TravelAgentHomeRemote.class);
       
TravelAgentRemote travelAgent = home.create( );
        
// Get a list of all cabins on ship 1 with a bed count of 3.
String list [] = travelAgent.listCabins(SHIP_ID,BED_COUNT);
        
for(int i = 0; i < list.length; i++)
{
   System.out.println(list[i]);
}
...

The client code does a JNDI lookup for the TravelAgent home and does a simple create( ) method invocation to obtain a reference to a TravelAgent EJB. The client then calls listCabins( ) and receives a list of cabin names that meet the provided criteria.

Let’s examine a little of the code in TravelAgent EJB’s listCabins( ) method to see how it works.

TravelAgentBean.java

public String [] listCabins(int shipID, int bedCount) 
{
   try 
   {
      javax.naming.Context jndiContext = new InitialContext( );
       Object obj = 
             jndiContext.lookup("java:comp/env/ejb/CabinHomeRemote");


       CabinHomeRemote home =
   ...

When a deployed EJB in JBoss wants to access JNDI, all that’s needed is a simple new InitialContext( ). JBoss will automatically create an optimized, in-process reference to the JNDI server running inside the application server, to avoid the overhead of a distributed network call when accessing it. The rest of listCabins( ) is pretty straightforward, so you can just go on to running the client application.

Run the Client_3 application by invoking ant run.client_42 at the command prompt. Remember to set your JBOSS_HOME and PATH environment variables.

The output of Client_3 should look something like this:

C:workbookex04_2>ant run.client_42
Buildfile: build.xml

prepare:

compile:

ejbjar:

run.client_42:
     [java] 1,Master Suite,1
     [java] 3,Suite 101,1
     [java] 5,Suite 103,1
     [java] 7,Suite 105,1
     [java] 9,Suite 107,1
     [java] 12,Suite 201,2
     [java] 14,Suite 203,2
     [java] 16,Suite 205,2
     [java] 18,Suite 207,2
     [java] 20,Suite 209,2
     [java] 22,Suite 301,3
     [java] 24,Suite 303,3
     [java] 26,Suite 305,3
     [java] 28,Suite 307,3
     [java] 30,Suite 309,3
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