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java Callable FutureTask Excecuter: How to listen to finished task

I'm quite new to executer services. Liked doing everything myself, but I think it's time to trust these services.

I want to hand by Executer a Runnable. The executer wraps that in a FutureTask and hands it back to me. Now I call poll the done() method. But I would like to be notified when then done() method would return true.

There is a get() method that blocks until the Runnable has finished, but then I would need a extra thread for every job, just to see when it's finished.

Can I hand my executer some extra Callable to get notified about the task finishing?

What's the way to go here? I could add some code to the end of the run method, but then done() might still be false...

Solution

  • If you can make a specific assumption of using a java.util.concurrent.ThreadPoolExecutor, then you can use its hook methods; afterExecute() and beforeExecute().

    http://download.oracle.com/javase/6/docs/api/java/util/concurrent/ThreadPoolExecutor.html

    They are not as elegant as the ListenableFuture, but it might be an adequate solution provided you need only one type of a "listener" for a given executor instance.