DelayQueue延迟队列的使用和场景

一个实现PriorityBlockingQueue实现延迟获取的无界队列,在创建元素时,可以指定多久才能从队列中获取当前元素。只有延时期满后才能从队列中获取元素。

使用场景:

1.定时任务调度。使用DelayQueue保存当天将会执行的任务和执行时间，一旦从DelayQueue中获取到任务就开始执行,从比如TimerQueue就是使用DelayQueue实现的。
2.缓存系统的设计：可以用DelayQueue保存缓存元素的有效期,使用一个线程循环查询DelayQueue,一旦能从DelayQueue中获取元素时,表示缓存有效期到了。
3.订单延迟支付关闭。(MQ延迟消息队列/时间轮/定时任务)

代码案例

package thread;

import java.util.concurrent.Delayed;
import java.util.concurrent.TimeUnit;

public class DelayQueueExampleTask implements Delayed {
    

    private String orderId;
    private long start = System.currentTimeMillis();
    private long time;

    public DelayQueueExampleTask(String orderId,long time) {
    
        this.orderId = orderId;
        this.time = time;
    }

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

    @Override
    public int compareTo(Delayed o) {
    
        return (int)(this.getDelay(TimeUnit.MILLISECONDS)-o.getDelay(TimeUnit.MILLISECONDS));
    }

    @Override
    public String toString() {
    
        return "DelayQueueExampleTask{" +
                "orderId='" + orderId + '\'' +
                ", start=" + start +
                ", time=" + time +
                '}';
    }
}

package thread;

import java.util.concurrent.DelayQueue;

public class DelayQueueExampleTaskTest {
    
    private static DelayQueue<DelayQueueExampleTask> delayQueue = new DelayQueue();
    public static void main(String[] args) {
    
        delayQueue.offer(new DelayQueueExampleTask("1001",1000));
        delayQueue.offer(new DelayQueueExampleTask("1002",2000));
        delayQueue.offer(new DelayQueueExampleTask("1003",3000));
        delayQueue.offer(new DelayQueueExampleTask("1004",5000));
        delayQueue.offer(new DelayQueueExampleTask("1005",6000));
        delayQueue.offer(new DelayQueueExampleTask("1006",7000));
        delayQueue.offer(new DelayQueueExampleTask("1007",8000));
        delayQueue.offer(new DelayQueueExampleTask("1008",3000));
        while(true){
    
            try {
    
                DelayQueueExampleTask task = delayQueue.take();
                System.out.println(task);
            } catch (InterruptedException e) {
    
                e.printStackTrace();
            }
        }
    }
}

执行效果: