EJB Refs ( coded name and JNDI name )

Question

Hi
I am just starting to develop EJBs . I can't get to work the EJB refs as expected . In a session bean I have a lookup for an Entity bean . Both beans are in separate JAR files , but in the same ear .
The lookup from session bean to entity bean only works when
the coded name in EJB ref is defined exactly the same as JNDI name for enity bean , also the name in lookup method must be the same in session bean .
To my surprise , the JNDI name for the target EJB , defined in EJB ref for session bean , does not mater at all . Even if I change it to a non existant name , the bean lookup works .
Theoritacally I understand that EJB ref is there to provide a mapping between the name of bean mentioned in code to the actual JNDI name of another bean , at the time of deployment .
The above is happening in J2EE 1.4 envoirment .
Please let me know , what am I doing here that is wrong .
( All examples and tutorials , usually give coded name same as JNDI name ) .
Thanks
Tarun

Answer 1

Hi Tarun,
The ejb-ref-name lives in a different namespace than the global JNDI names. Any names of ejb-refs, ejb-local-refs, resource-refs, etc. are scoped within a particular component's private namespace. All environment references are accessed via the java:comp/env namespace at runtime. So, if your ejb-ref-name(a.k.a "coded name") is ejb/foo in the deployment descriptor, you would access it from the code as follows :
initialContext.lookup("java:comp/env/ejb/foo");
This way, neither the standard deployment descriptor nor the code has any dependency on the global JNDI name. That's a good thing since the decision about which target EJB should be linked to is often not made until deployment time rather than development time. Furthermore, it means if you want to change the linking you can always do it without recompiling your code.
As for the global JNDI names, the first thing to note is that they are completely vendor-specific. That's why they don't appear in the standard deployment descriptor. In the J2EE SDK, each EJB that exposes a Remote view is assigned a global JNDI name in sun-ejb-jar.xml. This JNDI name is assigned from the global namespace of the application server. There's nothing stopping it from also being "ejb/foo", but it refers to a different thing than the "ejb/foo" above.
Now we have an ejb-ref called ejb/foo and an ejb whose JNDI name is ejb/foo, but we haven't linked the two. When it comes to linking, you have two choices:
1. If the target ejb is in the same .ear as the client component, you can use the ejb-link mechanism. This allows you to specify the target ejb by referring to its ejb-name. Since ejb-name is only guaranteed to be unique within an ejb-jar, the syntax allows for you to give the uri of the containing ejb-jar, followed by #, followed by ejb-name.
2. Alternatively, you can specify the global JNDI name of the target ejb using sun-ejb-jar.xml Note that this will work whether the target ejb is in the same .ear or not. However, it's the only option if the target ejb is in a different .ear. In this case, you would create an ejb-ref entry for the client component within the sun-ejb-jar.xml. e.g. :
<ejb>
<ejb-name>MyClientBean</ejb-name>
<ejb-ref>
<ejb-ref-name>ejb/foo</ejb-ref-name>
<jndi-name>ejb/foo</jndi-name>
</ejb-ref>
</ejb>
Again, it's just a coincidence that both names happen to be ejb/foo. They refer to different things.
When you do a global lookup from your code, initialContext.lookup('ejb/foo"), it will work in some environments because you're simply bypassing the level of indirection provided by your component environment and going straight to the global namespace. This is non-portable and not a good idea, since you've now tightly coupled the name of the target ejb to your client component. That means if it changes you need to recompile your code. Hope this helps.
--ken