浅谈 DelayQueue 延时队列

 前言：DelayQueue延时队列是阻塞队列中的一种，想了解其他阻塞队列，点击进来学习 BlockingQueue 阻塞队列_程序员大禹的博客-CSDN博客

一、什么是DelayQueue延时队列

是一个支持延时获取元素的无界阻塞队列。队列使用PriorityQueue来实现。队列中的元素必须实现Delayed接口，在创建元素时可以指定多久才能从队列中获取当前元素。只有在延迟期满时才能从队列中提取元素。

二、使用场景

1、用户下订单后，超过一段时间未支付，订单取消

2、停车场停车超时，发送短信通知；

三、代码示例

1、定义延时对象DelayEvent，需要实现Delayed接口。

import org.springframework.stereotype.Component;
import java.util.concurrent.Delayed;
import java.util.concurrent.TimeUnit;

@Component
public class DelayEvent implements java.util.concurrent.Delayed {

    //任务ID
    private int id;
    //数据
    private String data;
    // 插入时间
    private long startTime;
    // 在队列中的保留时间
    private long retainTime;


    public int getId() { return id;}

    public void setId(int id) {
        this.id = id;
    }
    public String getData() {
        return data;
    }

    public void setData(String data) {
        this.data = data;
    }
    public long getStartTime() {
        return startTime;
    }

    public void setStartTime(long startTime) {
        this.startTime = startTime;
    }
    public long getRetainTime() {
        return retainTime;
    }

    public void setRetainTime(long retainTime) {
        this.retainTime = retainTime;
    }


    public DelayEvent() {}

    public DelayEvent(int id, String data, long retainTime) {
        this.id = id;
        this.data = data;
        this.startTime = System.currentTimeMillis();
        this.retainTime = retainTime;
    }

   /**
     * 判定元素是否过期, 过期时间 - 当前时间
     *
     * @param unit
     * @return
     */

    @Override
    public long getDelay(TimeUnit unit) {
        return unit.convert((retainTime + startTime) - System.currentTimeMillis(), TimeUnit.MILLISECONDS);
    }

   /**
     * 确定先后顺序
     *
     * @param o
     * @return
     */
    @Override
    public int compareTo(Delayed o) {
        DelayEvent delayEvent = (DelayEvent) o;
        return (int) (this.getDelay(TimeUnit.MILLISECONDS) - o.getDelay(TimeUnit.MILLISECONDS));
    }


}

2、测试

public class TestMain {

 public static final DelayQueue<DelayEvent> queue = new DelayQueue<DelayEvent>();
    public static void main(String[] args) {

        //创建个线程放入任务到阻塞队列中
        Thread thread = new Thread(() -> {
            DelayEvent delayEvent1 = new DelayEvent(1, "任务1", 1000);
            DelayEvent delayEvent2 = new DelayEvent(2, "任务2", 6000);
            DelayEvent delayEvent3 = new DelayEvent(3, "任务3", 3000);
            DelayEvent delayEvent5 = new DelayEvent(5, "任务5", 5000);

            queue.add(delayEvent1);
            queue.add(delayEvent2);
            queue.add(delayEvent3);
            queue.add(delayEvent5);
        });

        thread.start();

        //从队列中取出数据
        try {
            while (true) {
                if (queue.size() > 0) {
                    DelayEvent event = (DelayEvent) queue.take();
                    String str = JSON.toJSONString(event);
                    System.out.println(str);
                }
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

    }

}

3、执行结果

{"data":"任务1","id":1,"retainTime":1000,"startTime":1651046995180}
{"data":"任务3","id":3,"retainTime":3000,"startTime":1651046995180}
{"data":"任务5","id":5,"retainTime":5000,"startTime":1651046995180}
{"data":"任务2","id":2,"retainTime":6000,"startTime":1651046995180}

四、DelayQueue相关API