Throw a Composite Exception in Java

Question

I'm using ExecutorService, Future and Callable to do parallel processing. Though the Callable's exception can be caught when invoking Future#get, how to catch all the exceptions thrown by all callables and then throw a huge, compound exception, like:

ExecutorService service = Executors.newFixedThreadPool(5);
List<Future<Void>> futures = new ArrayList<Future<Void>>();
futures.add(service.submit(new TaskA());
futures.add(service.submit(new TaskB());

for (Future<Void> future : futures) {
    try {
        future.get();
    } catch (Exception e) {
        // ???
    }
}

// throw the big exception here

service.shutdown();

Answer 1

If you want to associate multiple exceptions with a single throw, use addSuppressed on your outermost exception.

It won't help you much on the catch side, but comprehensive error handling is never easy, especially after joining multiple threads of control.

Answer 2

Maybe I'm missing something, but

public class CompositeException extends Exception {
    private List<Exception> exceptions = new ArrayList<Exception>();
    public List<Exception> getExceptions() {
        return exceptions;
    }
}

Instantiate one of these puppies and load it up with all the exceptions before throwing it.