How to handle exception from Callable

Question

I would like to know how to handle exceptions from my Callable when I use Void as a return type.

Something like this:

ExecutorService executor = Executors.newSingleThreadExecutor();
executor.submit(new Callable<Void>() {

        @Override
        public Void call() throws Exception {
            call a third party code where an exception is thrown...
            return null;
        }

});

Since I don't need any result from this callable I don't call get() on the Future returned from calling executor.submit(). Thus the exception is swallowed.

What is the right way to handle such exceptions?

Your code looks fishy to me. You can't even return null if you mention void as return type of the method — user3505725, Jul 31 '14 at 09:01
Actually, you can return null as long as the type is not primitive :) — Silviu Burcea, Jul 31 '14 at 09:02
@user3505725 the big Void is used to hold the Void.Type which is void.class — Yehia Awad, Jul 31 '14 at 09:06
http://stackoverflow.com/questions/8417903/exception-during-callable-execution => `Future.get` IS the right way ;) — Mik378, Jul 31 '14 at 09:08
@Mik378 That's a blocking call and defeats OP's purpose not to have blocking. — Marko Topolnik, Jul 31 '14 at 09:08
@MarkoTopolnik Nothing in the OP evokes the issue of blocking call. — Mik378, Jul 31 '14 at 09:15
@Mik378 It is implicit in using an executor service in the first place. — Marko Topolnik, Jul 31 '14 at 09:19

Arve · Accepted Answer · 2014-07-31T09:22:41.153

3

How about try/catch within your call() method? - I suppose it depends on what you want to do if an exception occurs.

public Void call() throws Exception {
    try {
        ThirdParty.doSomething();
    } catch(SomeTypeException e) {
        SomeErrorHandler.handleThisError(e); // E.g. report it to the user
    }
    return null;
}

edited Jul 31 '14 at 09:22

answered Jul 31 '14 at 09:05

Arve

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I just need to push the exception up in calling stack. Our application catches all runtime exceptions and shows a dialog for the user. – Jan Krakora Jul 31 '14 at 09:14
@Behnil That's obviously impossible for a task you fork off to another thread. That thread has its own call stack, where at the top is a call to your submitted task. There is no exception handler there if you don't put it in. – Marko Topolnik Jul 31 '14 at 09:17
It won't appear on the same stack, as it is executed on the thread of the Executor. – Arve Jul 31 '14 at 09:17

How to handle exception from Callable

1 Answers1