Callback between EJBs / local EJB calls - interface

Question

Can you register EJB A as callback in an MDB B?
B.register(Aref)
in B: A.callback()
What would be Aref if the EJBs use local calls?
SessionContext.getEJBLocalObject()?

Answer 1

What you ask is not really possible in the proposed way.
If B is a Message Driven Bean, then it's never possible to call a method on it. In the messaging paradigm, the type of the receiver of a message is unknown. You thus can't reference an instance of the MDB. Instead, you post messages to a queue or topic and if your MDB is configured to listen to that its onMessage() method will be invoked.
Secondly, in EJB you don't often pass references around like in your example code. What kind of EJB bean is A supposed to be? A stateless session bean, or a stateful session bean?
In case it's a stateless session bean, the instance might not matter and you can probably just inject it:
#MessageDriven
public class NSMessageDrivenBean implements MessageListener {
#EJB
private A yourABean;
public void onMessage(Message message) {
// process message and then call A
yourABean.someMethod();
}
}
If the callback needs to be done to a type that is unknown in advance (depending on the message being send), then one mechanism for this is via a JMS reply.
In the message being send to the message driven bean, you then include code like this:
message.setJMSReplyTo(someDestination);
message.setJMSCorrelationID(someCorrelationID);
someDestination represents your callback, it's a destination to which something is listening, and this something can then invoke the call on the stateless session bean (in the context of the client).
E.g. something like:
connection.createSession(false, Session.AUTO_ACKNOWLEDGE).createConsumer(someDestination).setMessageListener(
new MessageListener() {
#Override
public void onMessage(Message message) {
yourABean.someMethod();
}
}
In this case, someDestination can be a temporary destination.