使用redis实现延迟队列

思路

利用redis的zset数据结构
Zset本质就是Set结构上加了个排序的功能，除了添加数据value之外，还提供另一属性score，所以我们把时间放在score上 新开一个线程不断去轮询比对。、

代码

/**
 * @Auther: wwh
 * @Date: 2019-03-29 11:06
 * @Description:
 */
public class RedisDelayTest {

    private static final String ADDR = "127.0.0.1";
    private static final int PORT = 6379;
    private static JedisPool jedisPool = new JedisPool(ADDR, PORT);
    private static CountDownLatch cdl = new CountDownLatch(10);

    public static Jedis getJedis() {
        return jedisPool.getResource();
    }

    
    /**
     * 
     * @date: 2019-03-29 13:01
     * @param: * @param delayTime:  延迟多少秒执行
     * @return: * @return: void
     * @author: wwh 
     * @Description:  添加延迟任务
     */       
    public void addDelayMsg(int delayTime) {
        Calendar instance = Calendar.getInstance();
        instance.add(Calendar.SECOND, delayTime);
        RedisDelayTest.getJedis().zadd("taskId", (instance.getTimeInMillis()) / 1000,  "" + delayTime);
        System.out.println("添加延迟任务: 当前时间：" + new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date()));
        System.out.println((delayTime) + "秒后执行");
    }


    public static void consumerDelayMessage() {
        Jedis jedis = RedisDelayTest.getJedis();
        while (true) {
            Set<Tuple> taskSet = jedis.zrangeWithScores("taskId", 0, 0);
            if (taskSet == null || taskSet.isEmpty()) {
                try {
                    TimeUnit.MICROSECONDS.sleep(500);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                continue;
            }
            Tuple tuple = (Tuple) taskSet.toArray()[0];
            double score = tuple.getScore();
            Calendar instance = Calendar.getInstance();
            long nowTime = instance.getTimeInMillis() / 1000;
            if (nowTime >= score) {
                String element = tuple.getElement();
                Long taskId = jedis.zrem("taskId", element);
                if (taskId > 0) {
                    System.out.println(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date()) + ":redis消费了一个任务：消费的订单taskId为" + element);
                }
            }
        }
    }

    static class DelayMessage implements Runnable{
        @Override
        public void run() {
            try {
                cdl.await();
                consumerDelayMessage();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    public static void main(String[] args) {
        RedisDelayTest delayTest = new RedisDelayTest();
        delayTest.addDelayMsg(5);
        for (int i = 0; i < 10; i++) {
            new Thread(new DelayMessage()).start();
            cdl.countDown();
        }
    }
}

缺点

不支持分布式和集群。
最好还是用mq实现延迟队列。

参考

https://my.oschina.net/u/3266761/blog/1930360