[Java] CountDownLatch和ExecutorService的简单使用

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[Java] CountDownLatch和ExecutorService的简单使用

一、前言

• 环境说明：

JDK：1.8

官方API文档：https://docs.oracle.com/javase/8/docs/api/index.html

参考：

https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/CountDownLatch.html

https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ExecutorService.html

二、记录

场景说明：

1.模拟多个动物，同时喂食，并记录过程

• 动物接口

package com.demo.thread;/*** 动物接口* */
public interface IAnimal {/*** 喂食* */public String feeding() throws InterruptedException;}

• 动物类：狗

package com.demo.thread;/*** 狗* */
public class Dog implements IAnimal {@Overridepublic String feeding() throws InterruptedException {Thread.sleep(3000); // 模拟耗时StringBuffer stringBuffer = new StringBuffer();stringBuffer.append("准备美味的骨头");stringBuffer.append(" > 开始喂食");return stringBuffer.toString();}
}

• 动物类：猫

package com.demo.thread;/*** 猫* */
public class Cat implements IAnimal {@Overridepublic String feeding() throws InterruptedException {Thread.sleep(5000); // 模拟耗时StringBuffer stringBuffer = new StringBuffer();stringBuffer.append("准备美味的小鱼");stringBuffer.append(" > 开始喂食");return stringBuffer.toString();}
}

• 任务类：喂食

package com.demo.thread;import java.util.Map;
import java.util.concurrent.CountDownLatch;/*** 任务类* */
public class FeedingTask implements Runnable {private String id;private IAnimal iAnimal;private CountDownLatch countDownLatch;private Map<String, String> map; // 结果// constructorpublic FeedingTask(String id, IAnimal iAnimal, CountDownLatch countDownLatch, Map<String, String> map){this.id = id;this.iAnimal = iAnimal;this.countDownLatch = countDownLatch;this.map = map;}@Overridepublic void run() {try {long start = System.currentTimeMillis(); // 开始时间戳String flow = iAnimal.feeding(); // 开始喂食map.put(id, flow); // 记录过程long end = System.currentTimeMillis(); // 结束时间戳System.out.println(id + " exec="+ (end - start) +"ms");} catch (InterruptedException e) {e.printStackTrace();}finally {countDownLatch.countDown(); // 计数器递减}}
}

• 主入口

package com.demo.thread;import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;public class MainDemo {public static void main(String[] args) throws InterruptedException {Map<String, String> map = new HashMap<>();CountDownLatch countDownLatch = new CountDownLatch(2); // M 个喂食任务ExecutorService executorService = Executors.newFixedThreadPool(2); // N 个任务同时执行（线程池）// Dog FeedingexecutorService.execute(new FeedingTask("DOG", new Dog(), countDownLatch, map));// Cat FeedingexecutorService.execute(new FeedingTask("CAT", new Cat(), countDownLatch, map));// 等待所有动物喂食完成（等待计数器归零）countDownLatch.await();executorService.shutdown(); // 关闭执行线程池// 输出结果System.out.println(map.toString());}
}

• 输出结果

DOG exec=3000ms
CAT exec=5000ms
{CAT=准备美味的小鱼 > 开始喂食, DOG=准备美味的骨头 > 开始喂食}

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