消除EJB注释和注入

Question

I'm currently puzzled with the way Glassfish 3.1.2.2 handles EJBs.

I have an OSGi project, which consists of many OSGi bundles (jars). Also, there are a few WARs, including a Tapestry web application.

In one such bundle, let's call it "interfaces.jar", I have an interface defined:

public interface MyInterface() {
    public static final String JNDI_NAME = "java:global/MyInterface";
    void myMethod();
}

The implementation of that interface is as following, and it's contained in bundle "beans.jar":

@Stateless
@EJB(name = MyInterface.JNDI_NAME, beanInterface = MyInterface)
public class MyBean implements MyInterface() {
    void myMethod() {
        ...
    }
}

I am calling it from my Tapestry WAR app via JNDI lookup:

InitialContext.doLookup(MyInterface.JNDI_NAME);

Now, I was reading EJB 3.1 specification, and it says that I can one of the following scenarios:

1. Interface has @Local annotation; EJB is implementing this interface.
2. Interface is a plain Java interface without annotation; EJB with @Local annotation is implementing it.
3. Interface is a plain Java interface without annotation; EJB is implementing it.
4. Interface is a plain Java interface without annotation; EJB with @Local annotation is not implementing it.
5. EJB doesn't have any special annotations.

So, by elimination:

1. I don't have @Local on interface
2. I don't have @Local on EJB
3. Seems somewhat right
4. I don't have @Local on EJB
5. I have @EJB annotation on my EJB

So, it seems that it's case 3:

"Because it's the only implemented interface of the EJB, a container assumes that it must be a local business interface."

Now, a few questions:

1. Is my interface a local or remote one, since there is no local or remote annotation?
2. If it is local, I should be able to inject it with @EJB annotation, but it fails?
3. If it's remote, it is not in compliance with the explanation a few lines above?
4. If I add either @Local or @Remote , and perform JNDI lookup, I get a naming exception and NPE telling me there is nothing under that JNDI_NAME . How is that possible?
5. What exactly does @EJB(name = ..., beanInterface = ...) do on bean class and how does it interact with @Local and @Remote annotations?

Answer 1

1.) First, let's see your example without the "unnecessary" @EJB annotation

@Stateless
public class MyBean implements MyInterface() {
    void myMethod() {
        ...
    }
}

You can now see clearly, that the EJB implements only one interface. As you mentioned in the 3rd points, "Interface is a plain Java interface without annotation; EJB is implementing it.", so MyInterface is a Local Business Interface of the MyBean EJB.

2.)

You use wrong JNDI name for the lookup:

@Stateless
public class MyBean implements MyInterface() {
    ...

The global JNDI name of your EJB:

java:global[/app-name][/module-name]/MyBean[!interface-name]

The interface-name is "MyInterface", but it is optional if there are no other business interfaces for your beans, like here, so you can skip it.

You have to figure out what the application- and module-name is for your bean in case of OSGI. In a simple EJB application, the application-name is the name of the .ear file, and the module-name is the name of the .war/.jar file. application-name can be skipped if your module is not packaged in an ear.

So for example:

new InitialContext().lookup("java:global/myModuleName/MyBean");

5.)

@Stateless
@EJB(name = "MyInterface", beanInterface = MyInterface.class)
public class MyBean implements MyInterface() {
    void myMethod() {
        ...
    }
}

Here the @EJB annotation creates an EJB and put a reference to it into the Environment Naming Context (ENC). So it does nothing with the MyBean EJB, just expand its ENC with a new entry.

So from the business method of the current bean you can lookup for that new entry:

    void myMethod() {
        new InitialContext().lookup("java:comp/env/MyInterface")
    }

You can locate the bean's ENC by "java:comp/env/" JNDI name.

As you can see, the name parameter defines the name of the entry in the ENC.

The beanInterface defines the Business Interface of the created Bean. If the Bean has more business interfaces, then you have to define beanName too, so the container could determine wich Bean you would like to create.

You can read about this topic here: http://thegreyblog.blogspot.hu/2010/09/introduction-to-ejb-30-injection-and.html