How to use ScheduledExecutorService in java to call a Callable implementation at fixed interval?

Question

ScheduledExecutorService has methods like scheduleAtFixedRate(Runnable command,long initialDelay,long period,TimeUnit unit) to invoke Runnable classes at fixed intervals. I want my Thread to return some value after execution. So I implemented Callable interface. I could not find an equivalent method for invoking my Callable class at regular interval. Is there any other way to implement this? If this is functionality is not provided by Java, what is the rational behind that decision? Please let me know. Thanks.

Answer 1

You can't schedule Callable for periodic execution since it's unclear how to return a result from such an execution.

If you have your own approach to returning the result (for example, placing a result into a queue), you can wrap Callable into Runnable and implement your approach:

final BlockingQueue<Result> q = new ArrayBlockingQueue<Result>();
final Callable<Result> action = ...;

s.scheduleAtFixedRate(new Runnable() {
    public void run() {
        q.put(action.call());
    }
}, ...);