Java CountDownLatch完成异步回调实例详解

public class AsyncDemo {  private static void doSomeTask() {    System.out.println("Hello World");  }  private static void onCompletion() {    System.out.println("All tasks finished");  }  public static void main(String[] args) {    ExecutorService executor = Executors.newCachedThreadPool();    final CountDownLatch latch = new CountDownLatch(2);    executor.execute(new Task(latch));    executor.execute(new Task(latch));    executor.execute(() -> {      try {        latch.await();      } catch (InterruptedException e) {        e.printStackTrace();      }      onCompletion();    });    executor.shutdown();  }  private static class Task implements Runnable {    /**     * CountDownLatch 是JDK提供的一个简单的线程监测工具     * 基于简单的计数，调用countDown()方法表明当前线程已经终止     * 在监测线程中调用await()方法,该方法会一直挂起直到所有其它线程终止     */    private final CountDownLatch latch;    public Task(CountDownLatch latch) {      this.latch = latch;    }    @Override    public void run() {      try {        doSomeTask();      } catch (Exception e) {        e.printStackTrace();      } finally {        latch.countDown();      }    }  }}