Delayqueue usage and scenarios of delay queue

An implementation PriorityBlockingQueue Realize the boundless queue of delay acquisition , When you create an element , You can specify how long it takes to get the current element from the queue . Only after the delay expires can the element be retrieved from the queue .

Use scenarios :

1. Scheduled task scheduling . Use DelayQueue Save the tasks and execution time that will be performed on that day , Once from DelayQueue Get the task and start executing , From, for example TimerQueue Is the use of DelayQueue Realized .
2. The design of cache system ： It can be used DelayQueue Save the validity of the cache elements , Use a thread loop to query DelayQueue, Once you can get from DelayQueue When getting elements in , Indicates that the cache expiration date is .
3. Order late payment close .(MQ Delayed message queuing / Time wheel / Timing task )

Code case

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();
            }
        }
    }
}

Execution effect :