EJB 3.0 @Stateless @EJB @Resource and JNDI clarity..

Question

Hi,
I am trying to configure an EJB 3.0 but not able to do so properly.
I have a single business interface and 2 bean implementation class of the same business interface doing different things. How do I access the EJB's if I have the same business interface class.I am getting JNDI error while trying to lookup.
Also what does the "name" and "mappedName" in @Stateless(name ="...",mappedName="") signify.
Then in case of Dependency injection,how should I look for the EJB? What would be it's JNDI name in this case?
@EJB(name="",beanName="",mappedName="")
private HelloEJB hello;
What does the name,benaName and mappedName in case of an @EJB annotation signify??
Please clear me with these attributes of @Stateless and @EJB and @Resource. I am getting toatlly confused with what should be the logic name and what is the JNDI name????
Thanks

Answer 1

In @Stateless, @name() is the annotation equivalent of <ejb-name> in ejb-jar.xml. It gives a unique bean name identifier to the component within the ejb-jar. It is completely independent of mappedName. If no @Stateless name() is specified, it defaults to the unqualified bean class name.
In @Stateless, mappedName() is used to assign a global JNDI name to the bean's remote interface. This can be used to explicitly lookup the EJB reference to that interface or as one way to resolve a caller's EJB dependency.
In @EJB, if the target of the dependency lives within the same application, you can always fully resolve it using only beanName(). beanName() takes the value specified in @Stateless name(), or the default as described above.
@EJB name() assigns a name to the client dependency within the caller's component environment. It is optional. In most cases that value doesn't matter since if the dependency is being injected you never have to refer to the name() attribute anywhere else.
@EJB mappedName() is used to resolve an EJB dependency that spans applications. It holds a global JNDI name, e.g. the one specified in @Stateless mappedName(). mappedName() is not required to be supported by all vendors.
So, to sum it all up, it's fine to have two different beans that expose the same interface. E.g. :
@Stateless(name="A1", mappedName="A1Global")
public class A1 implements A { ... }
@Stateless(mappedName="A2Global") // name() defaults to "A2"
public class A2 implements A { ... }
In a caller within the same application :
@EJB(beanName="A1")
private A a;
@EJB(beanName="A2")
private A a;
In a caller within a different application :
@EJB(mappedName="A1Global")
private A a;
@EJB(mappedName="A2Global")
private A a;
You can find additional information in our EJB FAQ :
https://glassfish.dev.java.net/javaee5/ejb/EJB_FAQ.html#EJB_ejb-ref_ejb_local_ref