import java.util.concurrent.CountDownLatch;

import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;/** * CountDownLatch维护一个计数器,等待这个CountDownLatch的线程必须等到计数器为0时才可以继续. * 以下实例模拟服务器的启动,假设启动一个服务器需要初始化3个组件,当3个组件初始化完毕后,服务器才算成功启动. *//** * 使用CountDownLatch的关键技术点如下: * 1.构造CountDownLatch对象时,需要指定计数器的初始值,该值必须大于等于0,一旦对象被创建,其初始值将不能被改变. * 2.CountDownLatch的await方法使当前线程进入等待状态,直到计数器为0 * 3.CountDownLatch的 和countDown方法使计数器减1. */public class CountDownLatchTest { /** 初始化组件的线程 */ public static class ComponentThread implements Runnable { CountDownLatch latch; //计数器 int ID; //组件ID //构造方法 public ComponentThread(CountDownLatch latch, int ID) { this.latch = latch; this.ID = ID; } public void run() { //初始化组件 System.out.println("Initializing component " + ID); try { Thread.sleep(500 * ID); } catch (InterruptedException e) {} System.out.println("Component " + ID + " initialized!"); latch.countDown(); //将计数器减1 } } /** 启动服务器 */ public static void startServer() throws Exception { System.out.println("Server is starting."); //初始化一个初始值为3的CountDownLatch CountDownLatch latch = new CountDownLatch(3); //启动3个线程分别去3个组件 ExecutorService service = Executors.newCachedThreadPool(); service.submit(new ComponentThread(latch, 1)); service.submit(new ComponentThread(latch, 2)); service.submit(new ComponentThread(latch, 3)); service.shutdown(); latch.await();//等待3个组件的初始化工作都完成 System.out.println("Server is up!");//当所需的三个组件都完成时,Server就可以继续了 } public static void main(String... args) throws Exception { CountDownLatchTest.startServer(); }

本文转自远哥博客园博客，原文链接：http://www.cnblogs.com/taven/archive/2011/12/17/2291475.html，如需转载请自行联系原作者