Java set a callback from ExecutorService

Question

I have a fixedThreadPool that I am using to run a bunch of worker threads to achieve parallel execution of a task with many components.

When all threads have finishe

Answer 1

You can add a callback for when a thread returns in Java 8+ using CompletableFuture as in the following, where t is the result of your long-running computation,

CompletableFuture.supplyAsync(() -> {
    T t = new T();
    // do something
    return t;
}).thenApply(t -> {
    // process t
});

If you want to use callbacks in just Java 7, you could do something like,

int x = 10;
ExecutorService fixedThreadPool = Executors.newFixedThreadPool(x);
Future result = fixedThreadPool.submit(() -> {
    // do calculation
    return T;
});
fixedThreadPool.submit(() -> {
    long minutesToWait = 5;
    T t = null;
    try {
        t = result.get(minutesToWait, TimeUnit.MINUTES);
    } catch (InterruptedException | ExecutionException | TimeoutException e) {
        LOGGER.error(e);
    }
    if (t != null) {
        // process t
    }
});