Java, Design pattern : Multiple event sources and One event Handler

Question

Hello everybody,

I want to implement a design in Java where I have multiple event sources (Threads). Such event source accomplish a specific task and had to notify the unique Event Handler (Class) and this one have to accomplish other tasks according to event sources notifications.

My question is : how to implement this desiqn in the appropriate manner in Java? There is a design pattern similar to this design?

Thank you in advance :).

Answer 1

I think you are looking for the Observer pattern. Java does have some standard interfaces (java.util.Observer, java.util.Observable), though these are not type specific; so you might consider your own if the domain seems to require it.

class MyThread implements Runnable {
 Observable observable;

 public MyThread(EventHandler observer) {
  observable = new Observable();
  observable.addObserver(observer);
 }

 public void run() {
  while (!done())  {
   Object result = doStuff();
   observable.notifyObservers(result);
  }
 }
}

// might have this be singleton
class EventHandler implements Observer {
 public synchronized void update(Observable o, Object arg) {
  accomplishOtherTask();
 }
}

Answer 2

Hi,

Sounds like an actor pattern to me. Each thread acts as an actor, accomplishing one single task. Th eoutcome is set on a queue (yes) to be processed by the next actor.

I have no experience with java actor frameworks, though. Consult Google for that.

Answer 3

In GWT, this is called the event bus. Either GWT.HandlerManager or GWTx.PropertyChangeSupport are Google recommended implementations. The latter is available in J2SE since 1.4.2

Answer 4

Maybe I don't understand your question, but I think you don't need any design pattern, but something from the java.util.concurrent package.

A ThreadPoolExecutor ?