Question

I need to run a task inside a RMI service and it needs an event listener implemented for it. Right now when I pass the EventListener over RMI it does execute the call however the callback method of the Listener is not being invoked and it remains in the wait state. How should I get this to work?

public class MyEventListener implements Serializable, ABCEventListener {

    private static final long serialVersionUID = -4686421592620210489L;
    private boolean registrationCompleted = false;

    public boolean getRegistrationCompleted(){
        return registrationCompleted;
    }
    @Override
    public void onSomethingDiscovered(Agent agent) {            
        System.out.println("Added agent "+agent.toString()+" to the set \n");

    }

    @Override
    public void onDiscoveryComplete() {
        this.registrationCompleted = true;
        System.out.println("Discovery process completed. \n");
    }
}

Here is where I pass the eventlistener to the RMI service ‘ds’

MyEventListener myEL = new MyEventListener();
ds.discoverAsync(val, myEL);
waitForRegistration();
.
.
    private void waitForRegistration() {

    try{
    while(!dcev.getRegistrationCompleted()){
        System.out.println("Please wait...");
        Thread.sleep(15000);
    }
    }catch(InterruptedException e){
        logger.error("InterruptedException raised while waiting for registration",e);
        e.printStackTrace();
    }

}

Answer 1

The problem is that because your event listener is serializable the data fields of your event listener get sent across the wire and a new object created on the server side. The method is called on this copy of your event listener. This makes perfect sense for data objects, but for the likes of event listeners doesn’t work as you want your client code to get the call.

I believe you can make this work if your event listener extends RemoteObject. If you do this, instead of your object being copied, it will be exposed as an RMI service when you call the server. The server instead of getting a copy of your object, will get a proxy to your event listener. The call to the event listener will result in an RMI call in the reverse direction to call your event listener.

See Passing Remote Objects in the RMI guide for more details.