延时队列

最近刚学，本篇先给出一个实际使用的例子。
首先队列对象当然就是DelayQueue。而队列元素则需要实现Delayed这个接口，并实现该接口compareTo方法和getDelay方法。

首先定义该元素及其属性。

class DelayTask implements Delayed {
    public String name;
    public Long delayTime;
    public TimeUnit delayTimeUnit;
    public Long executeTime;//ms

    DelayTask(String name, long delayTime, TimeUnit delayTimeUnit) {
        this.name = name;
        this.delayTime = delayTime;
        this.delayTimeUnit = delayTimeUnit;
        this.executeTime = System.currentTimeMillis() + delayTimeUnit.toMillis(delayTime);
    }
}
   
   
   
   

    
    
    
    
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getDelay方法的作用即是计算当前时间到执行时间之间还有多长时间。
如下，返回unit单位下该延迟时间的值。

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

    
    
    
    
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compareTo方法的作用即是判断队列中元素的顺序谁前谁后。当前元素比队列元素后执行时，返回一个正数，比它先执行时返回一个负数，否则返回0.

@Override
public int compareTo(Delayed o) {
    if(this.getDelay(TimeUnit.MILLISECONDS) > o.getDelay(TimeUnit.MILLISECONDS)) {
        return 1;
    }else if(this.getDelay(TimeUnit.MILLISECONDS) < o.getDelay(TimeUnit.MILLISECONDS)) {
        return -1;
    }
    return 0;
}
   
   
   
   

    
    
    
    
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最后我们用个简单的方法测试下：

public static void main(String[] args) {
    DelayQueue queue = new DelayQueue<>();
    queue.add(new DelayTask("1", 1L, TimeUnit.SECONDS));
    queue.add(new DelayTask("2", 2L, TimeUnit.SECONDS));
    queue.add(new DelayTask("3", 3L, TimeUnit.SECONDS));

    System.out.println("queue put done");

    while(!queue.isEmpty()) {
        try {
            DelayTask task = queue.take();
            System.out.println(task.name + ":" + System.currentTimeMillis());

        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}
   
   
   
   

    
    
    
    
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运行结果如下：

queue put done
1:1504498317145
2:1504498318145
3:1504498319145

   
   
   
   

    
    
    
    
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下面是完整的代码：

public class DelayQueueTest {
    public static void main(String[] args) {
        DelayQueue queue = new DelayQueue<>();
        queue.add(new DelayTask("1", 1000L, TimeUnit.MILLISECONDS));
        queue.add(new DelayTask("2", 2000L, TimeUnit.MILLISECONDS));
        queue.add(new DelayTask("3", 3000L, TimeUnit.MILLISECONDS));

    System.out.println("queue put done");

    while(!queue.isEmpty()) {
        try {
            DelayTask task = queue.take();
            System.out.println(task.name + ":" + System.currentTimeMillis());

        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}


} 

class DelayTask implements Delayed { 

    public String name; 

    public Long delayTime; 

    public TimeUnit delayTimeUnit; 

    public Long executeTime;//ms

DelayTask(String name, long delayTime, TimeUnit delayTimeUnit) {
    this.name = name;
    this.delayTime = delayTime;
    this.delayTimeUnit = delayTimeUnit;
    this.executeTime = System.currentTimeMillis() + delayTimeUnit.toMillis(delayTime);
}


@Override
public int compareTo(Delayed o) {
    if(this.getDelay(TimeUnit.MILLISECONDS) > o.getDelay(TimeUnit.MILLISECONDS)) {
        return 1;
    }else if(this.getDelay(TimeUnit.MILLISECONDS) < o.getDelay(TimeUnit.MILLISECONDS)) {
        return -1;
    }
    return 0;
}

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


} 


   
   
   
   

    
    
    
    
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