// Disable new tasks from being submitted
executorService.shutdown();
try {
    // Wait a while for existing tasks to terminate
    if (!executorService.awaitTermination(500, TimeUnit.MILLISECONDS)) {
        // Cancel currently executing tasks
        executorService.shutdownNow();
    }
} catch (InterruptedException e) {
    // (Re-)Cancel if current thread also interrupted
    executorService.shutdownNow();
}