Java如何使用DelayQueue实现队列？

队列的大小不受限制，可以使添加立即返回，只有在延迟时间到期后才能从队列中获取元素。如果多个元素的延迟过期，则将首先使用延迟过期时间最长的元素。

package org.nhooo.example.util.concurrent;

import java.util.Random;
import java.util.UUID;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.DelayQueue;

public class DelayQueueExample {
    public static void main(String[] args) {
        // 使用DelayQueue创建阻塞队列的实例。
        final BlockingQueue<DelayObject> queue = new DelayQueue<>();
        final Random random = new Random();

        new Thread(new Runnable() {
            @Override
            public void run() {
                while (true) {
                    try {
                        // 将一些延迟的对象放入队列。
                        int delay = random.nextInt(10000);
                        DelayObject object = new DelayObject(UUID.randomUUID().toString(), delay);

                        System.out.printf("Put object = %s%n", object);
                        queue.put(object);
                        Thread.sleep(500);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        }, "Producer Thread").start();

        new Thread(new Runnable() {
            @Override
            public void run() {
                while (true) {
                    try {
                        // 从DelayQueue对象中取出元素。
                        DelayObject object = queue.take();
                        System.out.printf("[%s] - Take object = %s%n",
                                Thread.currentThread().getName(), object);
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        }, "Consumer Thread-1").start();

        new Thread(new Runnable() {
            @Override
            public void run() {
                while (true) {
                    try {
                        // 从DelayQueue对象中取出元素。
                        DelayObject object = queue.take();
                        System.out.printf("[%s] - Take object = %s%n",Thread.currentThread().getName(), object);
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        }, "Consumer Thread-2").start();
    }
}

下面是该Delayed接口的实现。在实现类中，我们必须实现getDelay(TimeUnit)和compareTo(Object)方法。

package org.nhooo.example.util.concurrent;

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

public class DelayObject implements Delayed  {
    private String data;
    private long startTime;

    public DelayObject(String data, long delay) {
        this.data = data;
        this.startTime = System.currentTimeMillis() + delay;
    }

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

    @Override
    public int compareTo(Delayed o) {
        if (this.startTime < ((DelayObject) o).startTime) {
            return -1;
        }
        if (this.startTime > ((DelayObject) o).startTime) {
            return 1;
        }
        return 0;
    }

    @Override
    public String toString() {
        return "{" +
                "data='" + data + ''' +
                ", startTime=" + startTime +
                '}';
    }
}

运行此示例将为您提供以下输出：

Put object = {data='dfe77bb9-b2b4-41d2-8b32-30b3eadae4d0', startTime=1347895148107}
Put object = {data='8f7881b3-fc0d-4c4d-b7e5-e0c2db126fc6', startTime=1347895142511}
Put object = {data='c8aa530b-38bf-4045-bcfa-5917f04bebab', startTime=1347895143447}
Put object = {data='7cc45157-2f10-4f19-8758-b43b47339fb0', startTime=1347895142971}
Put object = {data='d286bdf0-10d2-4371-8b85-1a830146d500', startTime=1347895150111}
Put object = {data='e1e100e7-4aee-44e2-b41b-92f0e1eacbc1', startTime=1347895145007}
[Consumer Thread-2] - Take object = {data='8f7881b3-fc0d-4c4d-b7e5-e0c2db126fc6', startTime=1347895142511}
Put object = {data='a2bba93c-9a9e-404f-ac57-7429c3ee0798', startTime=1347895149480}
[Consumer Thread-1] - Take object = {data='7cc45157-2f10-4f19-8758-b43b47339fb0', startTime=1347895142971}
Put object = {data='bfb74a00-d93a-43dd-b777-5f563657948a', startTime=1347895144808}