Chapter 23. Referencing EJB3 beans in EJB2.1 and vice versa

EJB3 beans may reference EJB2.1 and vice versa. This tutorial demonstrates mechanisms for such references.

To start, take a look at the EJB3 SLSB org.jboss.tutorial.reference21_30.bean.Stateless3Bean, the EJB2.1 SLSB org.jboss.tutorial.reference21_30.bean.Stateless2Bean and the deployment descriptors for the EJB2.1 SLSB ejb21_app/src/main/resources/META-INF/ejb-jar.xml and ejb21_app/src/main/resources/META-INF/jboss.xml:

				
<session>
   	<ejb-name>ejb/Stateless2</ejb-name>
   	<home>org.jboss.tutorial.reference21_30.bean.Stateless2Home</home>
   	<remote>org.jboss.tutorial.reference21_30.bean.Stateless2</remote>
   	<ejb-class>org.jboss.tutorial.reference21_30.bean.Stateless2Bean</ejb-class>
   	<session-type>Stateless</session-type>
   	<transaction-type>Container</transaction-type>
    <ejb-ref>
			<ejb-ref-name>ejb/Stateless3</ejb-ref-name>
			<ejb-ref-type>Session</ejb-ref-type>
			<home>org.jboss.tutorial.reference21_30.bean.Stateless3Home</home>
			<remote>org.jboss.tutorial.reference21_30.bean.Stateless3</remote>
	</ejb-ref>
</session>

Important

Notice, the ejb-jar.xml use a 2.x dtd for this EJB2.x application:

						
<!DOCTYPE ejb-jar PUBLIC "-//Sun Microsystems, Inc.//DTD Enterprise JavaBeans 2.0//EN"
                         "http://java.sun.com/dtd/ejb-jar_2_0.dtd">

The ejb-ref element references the 3.0 EJB. This mapping will make available the Stateless3 bean in the ENC (java:comp/env) namespace of the Stateless2 EJB.

Important

Observe carefully, the use of <home> and <remote> in the ejb-ref. Remember that we can provide a EJB2.1 view for an EJB3 bean. See the "ejb21_client_adaptors" for more details. We have intentionally exposed the home and remote view for the EJB3 Stateless3Bean so that it can be referenced by a EJB2.1 bean, without which the EJB2.1 bean would not have been able to reference this bean through its local ENC (because the home/remote are mandatory for a ejb-ref for EJB2.1 app)

						
@Stateless
@RemoteHome(Stateless3Home.class)
public class Stateless3Bean
{
...

						
public interface Stateless3Home extends EJBHome
{

   public Stateless3Remote create() throws java.rmi.RemoteException, javax.ejb.CreateException;
...

EJB3 referencing EJB2.1 bean:

Two mechanisms for referencing EJB2.1 from a EJB3 are demonstrated. The first mechanism uses annotations exclusively. Note the @EJBs annotation on org.jboss.tutorial.reference21_30.bean.Stateless3Bean. The name parameter for the @EJB specifies the name with which the 2.1 EJB will be bound in the ENC (java:comp/env) namespace of the Stateless3Bean. The mapped-name parameter specifies the global JNDI binding of the 2.1 EJB.

				
@EJBs(
{@EJB(name = "injected/Stateless2", mappedName = "Stateless2")})
public class Stateless3Bean
{
...

Note

The testAccess method in the Stateless3Bean looks up this EJB2.1 using the ENC jndi-name:

						
Stateless2Home home = (Stateless2Home) jndiContext.lookup(Container.ENC_CTX_NAME + "/env/injected/Stateless2");
Stateless2 test2 = home.create();

Also note that since the bean being looked up is a EJB2.1 bean, the lookup will return the home interface of the bean.

The second mechanism of referencing a EJB2.1 bean in a EJB3 bean is through the deployment descriptors. Take a look at the ejb3_app/src/main/resources/META-INF/ejb-jar.xml and ejb3_app/src/main/resources/META-INF/jboss.xml

				
<session>
	<ejb-name>Stateless3Bean</ejb-name>
	<ejb-ref>
		<ejb-ref-name>ejb/Stateless2</ejb-ref-name>
		<ejb-ref-type>Session</ejb-ref-type>
	</ejb-ref>
</session>

Important

The ejb-jar.xml should use the ejb-jar 3.0 xsd:

						
<ejb-jar
        xmlns="http://java.sun.com/xml/ns/javaee"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
                            http://java.sun.com/xml/ns/javaee/ejb-jar_3_0.xsd"
        version="3.0">

This binds the Stateless2 bean to the ENC (java:comp/env) namespace of the Stateless3Bean. Also take a look at the ejb3_app/src/main/resources/META-INF/jboss.xml which maps the global jndi name of the Stateless2 bean with the ejb-ref-name.

				
<session>
	<ejb-name>Stateless3Bean</ejb-name>
	<ejb-ref>
		<ejb-ref-name>ejb/Stateless2</ejb-ref-name>
		<jndi-name>Stateless2</jndi-name>
	</ejb-ref>
</session>

This reference is then used to inject the Stateless2 bean in the Stateless3Bean using @EJB annotation:

				
@EJB (name="ejb/Stateless2")
private Stateless2Home stateless2Home;

Note

The org.jboss.tutorial.reference21_30.bean.Stateless3Bean also exposes a business-remote interface, so that the org.jboss.tutorial.reference21_30.servlet.EJBReferenceServlet can use the business-remote interface.

					
@Stateless
@Remote(Stateless3.class)
@RemoteBinding(jndiBinding = "Stateless3")
public class Stateless3Bean
{
...

Important

There's a very important difference between the remote and a business-remote interface. The EJB2.x remote interfaces, which extend from EJBObject, are referred through the <remote> tag in the ejb-jar.xml. On the other hand, the EJB3 style Plain Old Java Interface which is implemented by your EJB3 style POJO bean is known as the business-remote interface and is represented by the @Remote and it's corresponding <business-remote> tag in ejb-jar.xml. Similar is the case with <local> and the <business-local> tags in ejb-jar.xml.

Building and Running

Note

To build and run the example, make sure you have installed JBoss 5.x. See the Section 1.1, “JBoss Application Server 5.x” for details.

From the command prompt, move to the "reference21_30" folder under the Section 1.3, “Set the EJB3_TUTORIAL_HOME”

Ant Users:

Make sure your JBossAS-5.x is running

	
$ ant

This will deploy the ear into the JBossAS-5.x server ("default" configuration).

To access the servlet, open a web browser and enter http://localhost:8080/jboss-ejb3-tutorial-reference21_30_webapp. This will bring up a page where you can click on the Test button to check that the EJB2.1 and EJB3 beans are referencing each other.

Maven Users: Make sure the AS is not running.

$ mvn clean install -PRunSingleTutorial

This will create the EAR in the target folder of the tutorial. Copy this EAR to the deploy folder of JBossAS-5.x and start the server (if it's already not started). Then follow the steps mentioned above, to access the servlet from the web browser.