小编给大家分享一下Java中CountDownLatch异步转同步工具类的示例分析，希望大家阅读完这篇文章之后都有所收获，下面让我们一起去探讨吧！
使用场景
由于公司业务需求，需要对接socket、MQTT等消息队列。
众所周知 socket 是双向通信，socket的回复是人为定义的，客户端推送消息给服务端，服务端的回复是两条线。无法像http请求有回复。
下发指令给硬件时，需要校验此次数据下发是否成功。
用户体验而言，点击按钮就要知道此次的下发成功或失败。
如上图模型，
第一种方案使用Tread.sleep
优点:占用资源小，放弃当前cpu资源
缺点: 回复速度快，休眠时间过长，仍然需要等待休眠结束才能返回，响应速度是固定的，无法及时响应第二种方案使用CountDownLatch
package com.lzy.demo.delay;import java.util.Map;import java.util.concurrent.ArrayBlockingQueue;import java.util.concurrent.ConcurrentHashMap;import java.util.concurrent.CountDownLatch;import java.util.concurrent.DelayQueue;import java.util.concurrent.Delayed;import java.util.concurrent.ExecutorService;import java.util.concurrent.ThreadPoolExecutor;import java.util.concurrent.TimeUnit;public class CountDownLatchPool { //countDonw池 private final static Map<Integer, CountDownLatch> countDownLatchMap = new ConcurrentHashMap<>(); //延迟队列 private final static DelayQueue<MessageDelayQueueUtil> delayQueue = new DelayQueue<>(); private volatile static boolean flag =false; //单线程池 private final static ExecutorService t = new ThreadPoolExecutor(1, 1, 0L, TimeUnit.MILLISECONDS, new ArrayBlockingQueue<>(1)); public static void addCountDownLatch(Integer messageId) { CountDownLatch countDownLatch = countDownLatchMap.putIfAbsent(messageId,new CountDownLatch(1) ); if(countDownLatch == null){ countDownLatch = countDownLatchMap.get(messageId); } try { addDelayQueue(messageId); countDownLatch.await(3L, TimeUnit.SECONDS); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("阻塞等待结束~~~~~~"); } public static void removeCountDownLatch(Integer messageId){ CountDownLatch countDownLatch = countDownLatchMap.get(messageId); if(countDownLatch == null) return; countDownLatch.countDown(); countDownLatchMap.remove(messageId); System.out.println("清除Map数据"+countDownLatchMap); } private static void addDelayQueue(Integer messageId){ delayQueue.add(new MessageDelayQueueUtil(messageId)); clearMessageId(); } private static void clearMessageId(){ synchronized (CountDownLatchPool.class){ if(flag){ return; } flag = true; } t.execute(()->{ while (delayQueue.size() > 0){ System.out.println("进入线程并开始执行"); try { MessageDelayQueueUtil take = delayQueue.take(); Integer messageId1 = take.getMessageId(); removeCountDownLatch(messageId1); System.out.println("清除队列数据"+messageId1); } catch (InterruptedException e) { e.printStackTrace(); } } flag = false; System.out.println("结束end----"); }); } public static void main(String[] args) throws InterruptedException { //提前创建线程，清空countdown new Thread(()->{ try { Thread.sleep(500L); removeCountDownLatch(1); } catch (InterruptedException e) { e.printStackTrace(); } }).start(); //开始阻塞 addCountDownLatch(1); //通过调整上面的sleep我们发现阻塞市场取决于countDownLatch.countDown()执行时间 System.out.println("阻塞结束----"); }}class MessageDelayQueueUtil implements Delayed { private Integer messageId; private long avaibleTime; public Integer getMessageId() { return messageId; } public void setMessageId(Integer messageId) { this.messageId = messageId; } public long getAvaibleTime() { return avaibleTime; } public void setAvaibleTime(long avaibleTime) { this.avaibleTime = avaibleTime; } public MessageDelayQueueUtil(Integer messageId){ this.messageId = messageId; //avaibleTime = 当前时间+ delayTime //重试3次，每次3秒+1秒的延迟 this.avaibleTime=3000*3+1000 + System.currentTimeMillis(); } @Override public long getDelay(TimeUnit unit) { long diffTime= avaibleTime- System.currentTimeMillis(); return unit.convert(diffTime,TimeUnit.MILLISECONDS); } @Override public int compareTo(Delayed o) { //compareTo用在DelayedUser的排序 return (int)(this.avaibleTime - ((MessageDelayQueueUtil) o).getAvaibleTime()); }}由于socket并不确定每次都会有数据返回，所以map的数据会越来越大，最终导致内存溢出
需定时清除map内的无效数据。
可以使用DelayedQuene延迟队列来处理，相当于给对象添加一个过期时间
使用方法 addCountDownLatch 等待消息,异步回调消息清空removeCountDownLatch
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