生成订单30分钟未支付，则自动取消，该怎么实现？

智能摘要文章源自JAVA秀-https://www.javaxiu.com/42308.html

本身的易用度要依赖于rabbitMq的运维.因为要引用rabbitMq，所以复杂度和成本变高。最近面试BAT，整理一份面试资料《Java面试BATJ通关手册》，覆盖了Java核心技术、JVM、Java并发、SSM、微服务、数据库、数据结构等等。文章源自JAVA秀-https://www.javaxiu.com/42308.html

原文约 3945 字 | 图片 8 张 | 建议阅读 8 分钟 | 评价反馈文章源自JAVA秀-https://www.javaxiu.com/42308.html

生成订单30分钟未支付，则自动取消，该怎么实现？

戳一戳→ 程序员的成长之路 文章源自JAVA秀-https://www.javaxiu.com/42308.html

文章源自JAVA秀-https://www.javaxiu.com/42308.html

程序员的成长之路文章源自JAVA秀-https://www.javaxiu.com/42308.html

互联网/程序员/技术/资料共享 文章源自JAVA秀-https://www.javaxiu.com/42308.html

关注文章源自JAVA秀-https://www.javaxiu.com/42308.html

阅读本文大概需要 10 分钟。文章源自JAVA秀-https://www.javaxiu.com/42308.html

来自：https://blog.csdn.net/hjm4702192/article/details/80519010文章源自JAVA秀-https://www.javaxiu.com/42308.html

# 引言

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

在开发中，往往会遇到一些关于延时任务的需求。例如文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

• 生成订单30分钟未支付，则自动取消文章源自JAVA秀-https://www.javaxiu.com/42308.html

• 生成订单60秒后,给用户发短信文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

对上述的任务，我们给一个专业的名字来形容，那就是延时任务。那么这里就会产生一个问题，这个延时任务和定时任务的区别究竟在哪里呢？一共有如下几点区别文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

1. 定时任务有明确的触发时间，延时任务没有文章源自JAVA秀-https://www.javaxiu.com/42308.html

2. 定时任务有执行周期，而延时任务在某事件触发后一段时间内执行，没有执行周期文章源自JAVA秀-https://www.javaxiu.com/42308.html

3. 定时任务一般执行的是批处理操作是多个任务，而延时任务一般是单个任务文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

下面，我们以判断订单是否超时为例，进行方案分析文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

# 方案分析

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

(1)数据库轮询

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

该方案通常是在小型项目中使用，即通过一个线程定时的去扫描数据库，通过订单时间来判断是否有超时的订单，然后进行update或delete等操作文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

博主当年早期是用quartz来实现的(实习那会的事)，简单介绍一下文章源自JAVA秀-https://www.javaxiu.com/42308.html

maven项目引入一个依赖如下所示文章源自JAVA秀-https://www.javaxiu.com/42308.html

<dependency><groupId>org.quartz-scheduler</groupId><artifactId>quartz</artifactId><version>2.2.2</version></dependency>

调用Demo类MyJob如下所示文章源自JAVA秀-https://www.javaxiu.com/42308.html

package com.rjzheng.delay1;import org.quartz.JobBuilder;import org.quartz.JobDetail;import org.quartz.Scheduler;import org.quartz.SchedulerException;import org.quartz.SchedulerFactory;import org.quartz.SimpleScheduleBuilder;import org.quartz.Trigger;import org.quartz.TriggerBuilder;import org.quartz.impl.StdSchedulerFactory;import org.quartz.Job;import org.quartz.JobExecutionContext;import org.quartz.JobExecutionException;publicclassMyJobimplementsJob{public void execute(JobExecutionContext context)throwsJobExecutionException {System.out.println("要去数据库扫描啦。。。"); }publicstatic void main(String[] args) throwsException {// 创建任务JobDetail jobDetail = JobBuilder.newJob(MyJob.class) .withIdentity("job1", "group1").build();// 创建触发器 每3秒钟执行一次Trigger trigger = TriggerBuilder .newTrigger() .withIdentity("trigger1", "group3") .withSchedule(SimpleScheduleBuilder.simpleSchedule() .withIntervalInSeconds(3).repeatForever()) .build();Scheduler scheduler = new StdSchedulerFactory().getScheduler();// 将任务及其触发器放入调度器 scheduler.scheduleJob(jobDetail, trigger);// 调度器开始调度任务 scheduler.start(); }}

运行代码，可发现每隔3秒，输出如下文章源自JAVA秀-https://www.javaxiu.com/42308.html

要去数据库扫描啦。。。文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

优缺点文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

优点:简单易行，支持集群操作文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

缺点:文章源自JAVA秀-https://www.javaxiu.com/42308.html

(1)对服务器内存消耗大文章源自JAVA秀-https://www.javaxiu.com/42308.html

(2)存在延迟，比如你每隔3分钟扫描一次，那最坏的延迟时间就是3分钟文章源自JAVA秀-https://www.javaxiu.com/42308.html

(3)假设你的订单有几千万条，每隔几分钟这样扫描一次，数据库损耗极大文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

(2)JDK的延迟队列文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

思路文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

该方案是利用JDK自带的DelayQueue来实现，这是一个无界阻塞队列，该队列只有在延迟期满的时候才能从中获取元素，放入DelayQueue中的对象，是必须实现Delayed接口的。文章源自JAVA秀-https://www.javaxiu.com/42308.html

DelayedQueue实现工作流程如下图所示文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

其中Poll():获取并移除队列的超时元素，没有则返回空文章源自JAVA秀-https://www.javaxiu.com/42308.html

take():获取并移除队列的超时元素，如果没有则wait当前线程，直到有元素满足超时条件，返回结果。文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

定义一个类OrderDelay实现Delayed，代码如下文章源自JAVA秀-https://www.javaxiu.com/42308.html

package com.rjzheng.delay2;import java.util.concurrent.Delayed;import java.util.concurrent.TimeUnit;publicclassOrderDelayimplementsDelayed{private String orderId;privatelong timeout; OrderDelay(String orderId, long timeout) {this.orderId = orderId;this.timeout = timeout + System.nanoTime(); }publicintcompareTo(Delayed other){if (other == this)return0; OrderDelay t = (OrderDelay) other;long d = (getDelay(TimeUnit.NANOSECONDS) - t .getDelay(TimeUnit.NANOSECONDS));return (d == 0) ? 0 : ((d < 0) ? -1 : 1); }// 返回距离你自定义的超时时间还有多少publiclonggetDelay(TimeUnit unit){return unit.convert(timeout - System.nanoTime(),TimeUnit.NANOSECONDS); }voidprint(){ System.out.println(orderId+"编号的订单要删除啦。。。。"); }}

运行的测试Demo为，我们设定延迟时间为3秒文章源自JAVA秀-https://www.javaxiu.com/42308.html

package com.rjzheng.delay2;import java.util.ArrayList;import java.util.List;import java.util.concurrent.DelayQueue;import java.util.concurrent.TimeUnit;publicclassDelayQueueDemo {publicstaticvoidmain(String[] args){ // TODO Auto-generated method stub  List<String> list = new ArrayList<String>(); list.add("00000001"); list.add("00000002"); list.add("00000003"); list.add("00000004"); list.add("00000005");  DelayQueue<OrderDelay> queue = newDelayQueue<OrderDelay>(); long start = System.currentTimeMillis(); for(int i = 0;i<5;i++){ //延迟三秒取出queue.put(new OrderDelay(list.get(i),  TimeUnit.NANOSECONDS.convert(3,TimeUnit.SECONDS))); try { queue.take().print();  System.out.println("After " +  (System.currentTimeMillis()-start) + " MilliSeconds");  } catch (InterruptedException e) { // TODO Auto-generated catch block  e.printStackTrace();  }  }  } }

输出如下文章源自JAVA秀-https://www.javaxiu.com/42308.html

00000001编号的订单要删除啦。。。。After3003 MilliSeconds00000002编号的订单要删除啦。。。。After6006 MilliSeconds00000003编号的订单要删除啦。。。。After9006 MilliSeconds00000004编号的订单要删除啦。。。。After12008 MilliSeconds00000005编号的订单要删除啦。。。。After15009 MilliSeconds

可以看到都是延迟3秒，订单被删除文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

优点:效率高,任务触发时间延迟低。文章源自JAVA秀-https://www.javaxiu.com/42308.html

缺点:文章源自JAVA秀-https://www.javaxiu.com/42308.html

(1)服务器重启后，数据全部消失，怕宕机文章源自JAVA秀-https://www.javaxiu.com/42308.html

(2)集群扩展相当麻烦文章源自JAVA秀-https://www.javaxiu.com/42308.html

(3)因为内存条件限制的原因，比如下单未付款的订单数太多，那么很容易就出现OOM异常文章源自JAVA秀-https://www.javaxiu.com/42308.html

(4)代码复杂度较高文章源自JAVA秀-https://www.javaxiu.com/42308.html

(3)时间轮算法

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

先上一张时间轮的图(这图到处都是啦)文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

时间轮算法可以类比于时钟，如上图箭头（指针）按某一个方向按固定频率轮动，每一次跳动称为一个 tick。这样可以看出定时轮由个3个重要的属性参数，ticksPerWheel（一轮的tick数），tickDuration（一个tick的持续时间）以及 timeUnit（时间单位），例如当ticksPerWheel=60，tickDuration=1，timeUnit=秒，这就和现实中的始终的秒针走动完全类似了。文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

如果当前指针指在1上面，我有一个任务需要4秒以后执行，那么这个执行的线程回调或者消息将会被放在5上。那如果需要在20秒之后执行怎么办，由于这个环形结构槽数只到8，如果要20秒，指针需要多转2圈。位置是在2圈之后的5上面（20 % 8 + 1）文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

我们用Netty的HashedWheelTimer来实现文章源自JAVA秀-https://www.javaxiu.com/42308.html

给Pom加上下面的依赖文章源自JAVA秀-https://www.javaxiu.com/42308.html

<dependency><groupId>io.netty</groupId><artifactId>netty-all</artifactId><version>4.1.24.Final</version></dependency>

测试代码HashedWheelTimerTest如下所示文章源自JAVA秀-https://www.javaxiu.com/42308.html

package com.rjzheng.delay3;import io.netty.util.HashedWheelTimer;import io.netty.util.Timeout;import io.netty.util.Timer;import io.netty.util.TimerTask;import java.util.concurrent.TimeUnit;publicclassHashedWheelTimerTest{staticclassMyTimerTaskimplementsTimerTask{boolean flag;publicMyTimerTask(boolean flag){this.flag = flag; }publicvoidrun(Timeout timeout)throws Exception {// TODO Auto-generated method stub System.out.println("要去数据库删除订单了。。。。");this.flag =false; } }publicstaticvoidmain(String[] argv){ MyTimerTask timerTask = new MyTimerTask(true); Timer timer = new HashedWheelTimer(); timer.newTimeout(timerTask, 5, TimeUnit.SECONDS);int i = 1;while(timerTask.flag){try { Thread.sleep(1000); } catch (InterruptedException e) {// TODO Auto-generated catch block e.printStackTrace(); } System.out.println(i+"秒过去了"); i++; } }}

输出如下文章源自JAVA秀-https://www.javaxiu.com/42308.html

1秒过去了2秒过去了3秒过去了4秒过去了5秒过去了要去数据库删除订单了。。。。6秒过去了

优缺点文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

优点:效率高,任务触发时间延迟时间比delayQueue低，代码复杂度比delayQueue低。文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

缺点:文章源自JAVA秀-https://www.javaxiu.com/42308.html

(1)服务器重启后，数据全部消失，怕宕机文章源自JAVA秀-https://www.javaxiu.com/42308.html

(2)集群扩展相当麻烦文章源自JAVA秀-https://www.javaxiu.com/42308.html

(3)因为内存条件限制的原因，比如下单未付款的订单数太多，那么很容易就出现OOM异常文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

(4)redis缓存文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

思路一文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

利用redis的zset,zset是一个有序集合，每一个元素(member)都关联了一个score,通过score排序来取集合中的值文章源自JAVA秀-https://www.javaxiu.com/42308.html

 zset常用命令文章源自JAVA秀-https://www.javaxiu.com/42308.html

• 添加元素:ZADD key score member [[score member] [score member] …]文章源自JAVA秀-https://www.javaxiu.com/42308.html

• 按顺序查询元素:ZRANGE key start stop [WITHSCORES]文章源自JAVA秀-https://www.javaxiu.com/42308.html

• 查询元素score:ZSCORE key member文章源自JAVA秀-https://www.javaxiu.com/42308.html

• 移除元素:ZREM key member [member …]文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

测试如下文章源自JAVA秀-https://www.javaxiu.com/42308.html

# 添加单个元素redis> ZADD page_rank 10 google.com(integer) 1# 添加多个元素redis> ZADD page_rank 9 baidu.com 8 bing.com(integer) 2redis> ZRANGE page_rank 0 -1 WITHSCORES1) "bing.com"2) "8"3) "baidu.com"4) "9"5) "google.com"6) "10"# 查询元素的score值redis> ZSCORE page_rank bing.com"8"# 移除单个元素redis> ZREM page_rank google.com(integer) 1redis> ZRANGE page_rank 0 -1 WITHSCORES1) "bing.com"2) "8"3) "baidu.com"4) "9"

那么如何实现呢？我们将订单超时时间戳与订单号分别设置为score和member,系统扫描第一个元素判断是否超时，具体如下图所示文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

文章源自JAVA秀-https://www.javaxiu.com/42308.html

package com.rjzheng.delay4;import java.util.Calendar;import java.util.Set;import redis.clients.jedis.Jedis;import redis.clients.jedis.JedisPool;import redis.clients.jedis.Tuple;publicclassAppTest{privatestaticfinal String ADDR = "127.0.0.1";privatestaticfinalint PORT = 6379;privatestatic JedisPool jedisPool = new JedisPool(ADDR, PORT);publicstatic Jedis getJedis(){return jedisPool.getResource(); }//生产者,生成5个订单放进去publicvoidproductionDelayMessage(){for(int i=0;i<5;i++){//延迟3秒 Calendar cal1 = Calendar.getInstance(); cal1.add(Calendar.SECOND, 3);int second3later = (int) (cal1.getTimeInMillis() / 1000); AppTest.getJedis().zadd("OrderId",second3later,"OID0000001"+i); System.out.println(System.currentTimeMillis()+"ms:redis生成了一个订单任务：订单ID为"+"OID0000001"+i); } }//消费者，取订单publicvoidconsumerDelayMessage(){ Jedis jedis = AppTest.getJedis();while(true){ Set<Tuple> items = jedis.zrangeWithScores("OrderId", 0, 1);if(items == null || items.isEmpty()){ System.out.println("当前没有等待的任务");try { Thread.sleep(500); } catch (InterruptedException e) {// TODO Auto-generated catch block e.printStackTrace(); }continue; }int score = (int) ((Tuple)items.toArray()[0]).getScore(); Calendar cal = Calendar.getInstance();int nowSecond = (int) (cal.getTimeInMillis() / 1000);if(nowSecond >= score){ String orderId = ((Tuple)items.toArray()[0]).getElement(); jedis.zrem("OrderId", orderId); System.out.println(System.currentTimeMillis() +"ms:redis消费了一个任务：消费的订单OrderId为"+orderId); } } }publicstaticvoidmain(String[] args){ AppTest appTest =new AppTest(); appTest.productionDelayMessage(); appTest.consumerDelayMessage(); }}

此时对应输出如下文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

可以看到，几乎都是3秒之后，消费订单。文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

然而，这一版存在一个致命的硬伤，在高并发条件下，多消费者会取到同一个订单号，我们上测试代码ThreadTest文章源自JAVA秀-https://www.javaxiu.com/42308.html

package com.rjzheng.delay4;import java.util.concurrent.CountDownLatch;publicclassThreadTest{privatestaticfinalint threadNum = 10;privatestatic CountDownLatch cdl = newCountDownLatch(threadNum);staticclassDelayMessageimplementsRunnable{publicvoidrun(){try { cdl.await(); } catch (InterruptedException e) {// TODO Auto-generated catch block e.printStackTrace(); } AppTest appTest =new AppTest(); appTest.consumerDelayMessage(); } }publicstaticvoidmain(String[] args){ AppTest appTest =new AppTest(); appTest.productionDelayMessage();for(int i=0;i<threadNum;i++){new Thread(new DelayMessage()).start(); cdl.countDown(); } }}

输出如下所示文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

显然，出现了多个线程消费同一个资源的情况。文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

解决方案文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

(1)用分布式锁，但是用分布式锁，性能下降了，该方案不细说。文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

(2)对ZREM的返回值进行判断，只有大于0的时候，才消费数据，于是将consumerDelayMessage()方法里的文章源自JAVA秀-https://www.javaxiu.com/42308.html

if(nowSecond >= score){String orderId = ((Tuple)items.toArray()[0]).getElement(); jedis.zrem("OrderId", orderId); System.out.println(System.currentTimeMillis()+"ms:redis消费了一个任务：消费的订单OrderId为"+orderId);}

修改为文章源自JAVA秀-https://www.javaxiu.com/42308.html

if(nowSecond >= score){ String orderId = ((Tuple)items.toArray()[0]).getElement();Long num = jedis.zrem("OrderId", orderId);if( num != null && num>0){ System.out.println(System.currentTimeMillis()+"ms:redis消费了一个任务：消费的订单OrderId为"+orderId); }}

在这种修改后，重新运行ThreadTest类，发现输出正常了文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

思路二文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

该方案使用redis的Keyspace Notifications，中文翻译就是键空间机制，就是利用该机制可以在key失效之后，提供一个回调，实际上是redis会给客户端发送一个消息。是需要redis版本2.8以上。文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

实现二文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

在redis.conf中，加入一条配置文章源自JAVA秀-https://www.javaxiu.com/42308.html

notify-keyspace-events Ex

运行代码如下文章源自JAVA秀-https://www.javaxiu.com/42308.html

package com.rjzheng.delay5;import redis.clients.jedis.Jedis;import redis.clients.jedis.JedisPool;import redis.clients.jedis.JedisPubSub;publicclassRedisTest {privatestatic final String ADDR = "127.0.0.1";privatestatic final int PORT = 6379;privatestatic JedisPool jedis = new JedisPool(ADDR, PORT);privatestatic RedisSub sub = new RedisSub();publicstaticvoidinit() {new Thread(new Runnable() {publicvoidrun() { jedis.getResource().subscribe(sub, "__keyevent@0__:expired"); } }).start(); }publicstaticvoidmain(String[] args) throws InterruptedException { init();for(int i =0;i<10;i++){ String orderId = "OID000000"+i; jedis.getResource().setex(orderId, 3, orderId); System.out.println(System.currentTimeMillis()+"ms:"+orderId+"订单生成"); } }staticclassRedisSubextendsJedisPubSub { <ahref='http://www.jobbole.com/members/wx610506454'>@Override</a>publicvoidonMessage(String channel, String message) { System.out.println(System.currentTimeMillis()+"ms:"+message+"订单取消"); } }}

输出如下文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

可以明显看到3秒过后，订单取消了文章源自JAVA秀-https://www.javaxiu.com/42308.html

ps:redis的pub/sub机制存在一个硬伤，官网内容如下文章源自JAVA秀-https://www.javaxiu.com/42308.html

原:Because Redis Pub/Sub is fire and forget currently there is no way to use this feature if your application demands reliable notification of events, that is, if your Pub/Sub client disconnects, and reconnects later, all the events delivered during the time the client was disconnected are lost.文章源自JAVA秀-https://www.javaxiu.com/42308.html

翻: Redis的发布/订阅目前是即发即弃(fire and forget)模式的，因此无法实现事件的可靠通知。也就是说，如果发布/订阅的客户端断链之后又重连，则在客户端断链期间的所有事件都丢失了。因此，方案二不是太推荐。当然，如果你对可靠性要求不高，可以使用。文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

优点:文章源自JAVA秀-https://www.javaxiu.com/42308.html

(1)由于使用Redis作为消息通道，消息都存储在Redis中。如果发送程序或者任务处理程序挂了，重启之后，还有重新处理数据的可能性。文章源自JAVA秀-https://www.javaxiu.com/42308.html

(2)做集群扩展相当方便文章源自JAVA秀-https://www.javaxiu.com/42308.html

(3)时间准确度高文章源自JAVA秀-https://www.javaxiu.com/42308.html

缺点:文章源自JAVA秀-https://www.javaxiu.com/42308.html

(1)需要额外进行redis维护文章源自JAVA秀-https://www.javaxiu.com/42308.html

(5)使用消息队列

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

我们可以采用rabbitMQ的延时队列。RabbitMQ具有以下两个特性，可以实现延迟队列文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

• RabbitMQ可以针对Queue和Message设置 x-message-tt，来控制消息的生存时间，如果超时，则消息变为dead letter文章源自JAVA秀-https://www.javaxiu.com/42308.html

• lRabbitMQ的Queue可以配置x-dead-letter-exchange 和x-dead-letter-routing-key（可选）两个参数，用来控制队列内出现了deadletter，则按照这两个参数重新路由。结合以上两个特性，就可以模拟出延迟消息的功能,具体的，我改天再写一篇文章，这里再讲下去，篇幅太长。文章源自JAVA秀-https://www.javaxiu.com/42308.html

 文章源自JAVA秀-https://www.javaxiu.com/42308.html

优点: 高效,可以利用rabbitmq的分布式特性轻易的进行横向扩展,消息支持持久化增加了可靠性。文章源自JAVA秀-https://www.javaxiu.com/42308.html

缺点：本身的易用度要依赖于rabbitMq的运维.因为要引用rabbitMq,所以复杂度和成本变高。文章源自JAVA秀-https://www.javaxiu.com/42308.html

<END>文章源自JAVA秀-https://www.javaxiu.com/42308.html

推荐阅读：文章源自JAVA秀-https://www.javaxiu.com/42308.html

无需安装！1秒钟让你体验Windows 11文章源自JAVA秀-https://www.javaxiu.com/42308.html

面试官：Spring AOP、AspectJ、CGLIB 都是什么鬼？它们有什么关系？文章源自JAVA秀-https://www.javaxiu.com/42308.html

最近面试BAT，整理一份面试资料《Java面试BATJ通关手册》，覆盖了Java核心技术、JVM、Java并发、SSM、微服务、数据库、数据结构等等。

文章源自JAVA秀-https://www.javaxiu.com/42308.html

获取方式：点个「在看」，点击上方小卡片，进入公众号后回复「面试题」领取，更多内容陆续奉上。文章源自JAVA秀-https://www.javaxiu.com/42308.html

朕已阅 文章源自JAVA秀-https://www.javaxiu.com/42308.html