Question

Say that I have the following code:

ExecutorService executor = Executors.newSingleThreadExecutor();
executor.execute(myRunnable);

Now, if myRunnable throws a RuntimeExcpetion, how can I catch it? One way would be to supply my own ThreadFactory implementation to newSingleThreadExecutor() and set custom uncaughtExceptionHandlers for the Threads that come out of it. Another way would be to wrap myRunnable to a local (anonymous) Runnable that contains a try-catch -block. Maybe there are other similar workarounds too. But… somehow this feels dirty, I feel that it shouldn’t be this complicated. Is there a clean solution?

Answer 1

The clean workaround is to use ExecutorService.submit() instead of execute(). This returns you a Future which you can use to retrieve the result or exception of the task:

ExecutorService executor = Executors.newSingleThreadExecutor();
Runnable task = new Runnable() {
  public void run() {
    throw new RuntimeException("foo");
  }
};

Future<?> future = executor.submit(task);
try {
  future.get();
} catch (ExecutionException e) {
  Exception rootException = e.getCause();
}