Register Observer Programmatically using CDI?

[paulmooney]

Is there a way to programmatically register an observer? I've noticed there is an interface for an ObserverMethod, but I haven't been able to find a place in CDI to register an observer programmatically as opposed to decoratively.

[nickarls]

Probably not in pure CDI but you might want be able to by casting to a Weld BeanManagerImpl. Never done it so I haven't checked if it's usable (resolving reset etc)

[paulmooney]

Thanks, I'll try out the BeanManagerImpl.addObserver() method. I'm okay with not going pure CDI, it just would have been a nice to have.

Now the challenge is going to be handling the lifecycle of these non-contextual/non-managed java objects I want to have observers for.

[swd847]

There is also AfterBeanDiscovery.addObserverMethod()

[swiegersf.francois.swiegers.gmail.com]

Your use case statement is a bit vague, so this may not be what you are looking for, but it should be possible to add observers dynamically at runtime using a normal Observer pattern.

(warning, I'm coding out of my head so the below won't compile, but I hope you get the general idea).

Like so:

@ApplicationScoped
public class Observer {

  private Set<Listener> myListeners ...;

  public void addSomeListener(Listener l) {
    myListeners.add(l);
  }

  public void afterEvent(@Observes SomeEvent event) {
    for (Listener l : myListeners) { //not thread safe!
      l.notify(event);
    }
  }

}

Then add a observer dynamically:

public class SomeClass {

 @Inject Observer observer;

 public void readyToRegisterMyObserver() {
   observer.addSomeListener(new Listener() ...);
 }

}

Of course, all the usual disclaimers regarding the fragile observer pattern applies.