复制代码 代码如下:
package com.yao;

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

/**
* CountDownLatch是个计数器，它有一个初始数，
* 等待这个计数器的线程必须等到计数器倒数到零时才可继续。
*/
public class CountDownLatchTest {

/**
* 初始化组件的线程
*/
public static class ComponentThread implements Runnable {
// 计数器
CountDownLatch latch;
// 组件ID
int 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!");
//将计数器减一
latch.countDown();
}
}

/**
* 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);
//起3个线程分别去启动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();

//等待3个组件的初始化工作都完成
latch.await();

//当所需的三个组件都完成时，Server就可继续了
System.out.println("Server is up!");
}

public static void main(String[] args) throws Exception {
CountDownLatchTest.startServer();
}
}