生成deamon线程的executor

参考SwingWorker代码：

   /**
     * returns workersExecutorService.
     *
     * returns the service stored in the appContext or creates it if
     * necessary.
     *
     * @return ExecutorService for the {@code SwingWorkers}
     */
    private static synchronized ExecutorService getWorkersExecutorService() {
        final AppContext appContext = AppContext.getAppContext();
        ExecutorService executorService =
            (ExecutorService) appContext.get(SwingWorker.class);
        if (executorService == null) {
            //this creates daemon threads.
            ThreadFactory threadFactory =
                new ThreadFactory() {
                    final ThreadFactory defaultFactory =
                        Executors.defaultThreadFactory();
                    public Thread newThread(final Runnable r) {
                        Thread thread =
                            defaultFactory.newThread(r);
                        thread.setName("SwingWorker-"
                            + thread.getName());
                        thread.setDaemon(true);
                        return thread;
                    }
                };

            executorService =
                new ThreadPoolExecutor(MAX_WORKER_THREADS, MAX_WORKER_THREADS,
                                       10L, TimeUnit.MINUTES,
                                       new LinkedBlockingQueue<Runnable>(),
                                       threadFactory);
            appContext.put(SwingWorker.class, executorService);

            // Don't use ShutdownHook here as it's not enough. We should track
            // AppContext disposal instead of JVM shutdown, see 6799345 for details
            final ExecutorService es = executorService;
            appContext.addPropertyChangeListener(AppContext.DISPOSED_PROPERTY_NAME,
                new PropertyChangeListener() {
                    @Override
                    public void propertyChange(PropertyChangeEvent pce) {
                        boolean disposed = (Boolean)pce.getNewValue();
                        if (disposed) {
                            final WeakReference<ExecutorService> executorServiceRef =
                                new WeakReference<ExecutorService>(es);
                            final ExecutorService executorService =
                                executorServiceRef.get();
                            if (executorService != null) {
                                AccessController.doPrivileged(
                                    new PrivilegedAction<Void>() {
                                        public Void run() {
                                            executorService.shutdown();
                                            return null;
                                        }
                                    }
                                );
                            }
                        }
                    }
                }
            );
        }
        return executorService;
    }