Page added by David Blevins

Overview

This example shows how to configure JNDI to lookup other EJBs using either the @EJB annotation or the ejb-jar.xml deployment descriptor.

There are a couple interesting aspects in this example intended to flush out some of the more confusing, and perhaps frustrating, aspects of referring to EJBs.

beans themselves do not have JNDI names (this was only recently added in Java EE 6)

This is the most frustrating and hard to accept. Java EE 5 does not have a global namespace and therefore there is no singular name for your EJB. It does not matter what you do to your EJB, there is no standard way to "give" the bean a name that can be used by the application globally.

each EJB owns it's own private java:comp/env namespace (java:comp/env is not global and cannot be treated that way)
names do not magically appear in "java:comp/env", they must be explicitly added.
to get a reference to bean B in the java:comp/env namespace of bean A, bean A must declare a reference to bean B.

You read this right. If you have 10 EJBs and all want to refer to bean B, then you must declare bean B as a reference 10 times (once for each of the 10 beans). There is no standard way in Java EE 5 to do this just once for all beans. In Java EE 6 there is a "java:global" namespace, a "java:app" namespace, and a "java:module" namespace where names can be defined with the desired scope.

There are two things which make this even more confusing:

Servlets have always defined "java:comp/env" differently. In a webapp, the "java:comp/env" namespace is shared by all servlets. This is essentially equivalent to the "java:module" namespace in Java EE 6. Understand there is a conflict in definition here and that for EJBs, "java:comp" is scoped at the component (the EJB itself) not the module as with webapps.
All vendors have some proprietary concept of global JNDI. So you may be able to lookup "java:/MyBean" or "MyBeanLocal", but these are vendor-specific and non-portable.

As well this example shows some other interesting aspects of referring to EJBs:

Two beans may use the same business interfaces, the interface alone does not necessarily identify the exact bean
circular references are possible

To illustrate all of this, we have two simple @Stateless beans, RedBean and BlueBean. Both implement the same business local interface, Friend. Both RedBean and BlueBean define java:comp/env/myFriend differently which is allowed as java:comp is a namespace that is private to each bean and not visible to other beans – so the names do not have to match.

The source for this example is the "lookup-of-ejbs" directory located in the openejb-examples.zip available on the download page.

The Code

Here we show the code for RedBean and BlueBean and their shared business local interface Friend.

@Stateless
@EJB(beanInterface = Friend.class, beanName = "BlueBean", name = "myFriend")
public class RedBean implements Friend {


    public String sayHello() {
        return "Red says, Hello!";
    }

    public String helloFromFriend() {
        try {
            Friend friend = (Friend) new InitialContext().lookup("java:comp/env/myFriend");
            return "My friend " + friend.sayHello();
        } catch (NamingException e) {
            throw new EJBException(e);
        }
    }
}

@Stateless
@EJB(beanInterface = Friend.class, beanName = "RedBean", name = "myFriend")
public class BlueBean implements Friend {

	public String sayHello() {
		return "Blue says, Hello!";
	}

    public String helloFromFriend() {
        try {
            Friend friend = (Friend) new InitialContext().lookup("java:comp/env/myFriend");
            return "My friend " + friend.sayHello();
        } catch (NamingException e) {
            throw new EJBException(e);
        }
    }
}

@Local
public interface Friend {
	
    public String sayHello();
    public String helloFromFriend();
	
}

The key items in the above are the following:

@EJB has been used at the class level to declare myFriend in the java:comp/env namespace of each EJB
because both beans share the same interface, Friend, we need to add beanName to the @EJB usage to specify the exact EJB we want
for BlueBean the java:comp/env/myFriend name has been configured to point to RedBean
for RedBean the java:comp/env/myFriend name has been configured to point to BlueBean

Alternative to annotations

If there is a desire to not use annotations, the above annotation usage is equivalent to the following ejb-jar.xml

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<ejb-jar xmlns="http://java.sun.com/xml/ns/javaee">
    <enterprise-beans>
        <session>
            <ejb-name>BlueBean</ejb-name>
            <business-local>org.superbiz.ejblookup.Friend</business-local>
            <ejb-class>org.superbiz.ejblookup.BlueBean</ejb-class>
            <session-type>Stateless</session-type>
            <transaction-type>Container</transaction-type>
            <ejb-local-ref>
                <ejb-ref-name>myFriend</ejb-ref-name>
                <local>org.superbiz.ejblookup.Friend</local>
                <ejb-link>RedBean</ejb-link>
            </ejb-local-ref>
        </session>
        <session>
            <ejb-name>RedBean</ejb-name>
            <business-local>org.superbiz.ejblookup.Friend</business-local>
            <ejb-class>org.superbiz.ejblookup.RedBean</ejb-class>
            <session-type>Stateless</session-type>
            <transaction-type>Container</transaction-type>
            <ejb-local-ref>
                <ejb-ref-name>myFriend</ejb-ref-name>
                <local>org.superbiz.ejblookup.Friend</local>
                <ejb-link>BlueBean</ejb-link>
            </ejb-local-ref>
        </session>
    </enterprise-beans>
</ejb-jar>

Writing a unit test for the example

Writing an unit test for this example is quite simple. We need just to write a setup method to create and initialize the InitialContext, and then write our test methods

public class EjbDependencyTest extends TestCase {

    private InitialContext initialContext;

    protected void setUp() throws Exception {
        Properties properties = new Properties();
        properties.setProperty(Context.INITIAL_CONTEXT_FACTORY, "org.apache.openejb.client.LocalInitialContextFactory");

        initialContext = new InitialContext(properties);
    }

    public void testRed() throws Exception {

        Friend red = (Friend) initialContext.lookup("RedBeanLocal");

        assertNotNull(red);
        assertEquals("Red says, Hello!", red.sayHello());
    	assertEquals("My friend Blue says, Hello!", red.helloFromFriend());

    }

    public void testBlue() throws Exception {

        Friend blue = (Friend) initialContext.lookup("BlueBeanLocal");

        assertNotNull(blue);
        assertEquals("Blue says, Hello!", blue.sayHello());
        assertEquals("My friend Red says, Hello!", blue.helloFromFriend());

    }

}

Running

Running the example is fairly simple. In the "lookup-of-ejbs" directory of the examples zip, just run:

$ mvn clean install

Which should create output like the following.

-------------------------------------------------------
 T E S T S
-------------------------------------------------------
Running org.superbiz.ejblookup.EjbDependencyTest
Apache OpenEJB 3.1.5-SNAPSHOT    build: 20101129-09:51
http://openejb.apache.org/
INFO - openejb.home = /Users/dblevins/work/openejb-3.1.x/examples/lookup-of-ejbs
INFO - openejb.base = /Users/dblevins/work/openejb-3.1.x/examples/lookup-of-ejbs
INFO - Configuring Service(id=Default Security Service, type=SecurityService, provider-id=Default Security Service)
INFO - Configuring Service(id=Default Transaction Manager, type=TransactionManager, provider-id=Default Transaction Manager)
INFO - Found EjbModule in classpath: /Users/dblevins/work/openejb-3.1.x/examples/lookup-of-ejbs/target/classes
INFO - Beginning load: /Users/dblevins/work/openejb-3.1.x/examples/lookup-of-ejbs/target/classes
INFO - Configuring enterprise application: classpath.ear
INFO - Configuring Service(id=Default Stateless Container, type=Container, provider-id=Default Stateless Container)
INFO - Auto-creating a container for bean BlueBean: Container(type=STATELESS, id=Default Stateless Container)
INFO - Enterprise application "classpath.ear" loaded.
INFO - Assembling app: classpath.ear
INFO - Jndi(name=BlueBeanLocal) --> Ejb(deployment-id=BlueBean)
INFO - Jndi(name=RedBeanLocal) --> Ejb(deployment-id=RedBean)
INFO - Created Ejb(deployment-id=RedBean, ejb-name=RedBean, container=Default Stateless Container)
INFO - Created Ejb(deployment-id=BlueBean, ejb-name=BlueBean, container=Default Stateless Container)
INFO - Deployed Application(path=classpath.ear)
Tests run: 2, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 1.244 sec

Results :

Tests run: 2, Failures: 0, Errors: 0, Skipped: 0

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Lookup of other EJBs Example