BlockingQueue之DelayQueue的学习使用

Posted 2020-11-18 jinjian91

DelayQueue 是一中阻塞队列,需要实现接口Delayed定义的方法.做下使用记录和心得吧,

@Data
public class DelayQueueExample implements Delayed {

    private String beginTime;
    private String name;

   public static DateTimeFormatter dateTimeFormatter=DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
    public  LocalDateTime localDateTime;

    public DelayQueueExample(String beginTime, String name) {
        this.beginTime = beginTime ;
        this.name = name;
    }

    @Override
    public long getDelay(TimeUnit unit) {

        // TimeUnit.NANOSECONDS.convert(1000,TimeUnit.DAYS);
        //long ss= unit.convert(afterTime - System.nanoTime(), TimeUnit.MILLISECONDS);
       // System.out.println("getDelay()"+ss);
       //unit.convert(afterTime - System.nanoTime(), TimeUnit.MILLISECONDS)

        //与当前时间对比,小于当前时间的话就进入队列,否则就抛弃这个队列的数据
        localDateTime=  LocalDateTime.parse(beginTime,dateTimeFormatter);
        return localDateTime.toInstant(ZoneOffset.of("+8")).toEpochMilli()- System.currentTimeMillis();//是否小于当前时间

    }

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

    @Override
    public String toString() {
        return "DelayQueueExample{" +
                "beginTime=" +(beginTime) +
                ", name=‘" + name + ‘‘‘ +
                ‘}‘;
    }


    public static void main(String[] args) throws InterruptedException {
        DelayQueue<DelayQueueExample> delayQueue = new DelayQueue<DelayQueueExample>();
        delayQueue.add(new DelayQueueExample("2018-06-18 00:45:00", "hhe100"));
        delayQueue.add(new DelayQueueExample("2018-06-18 00:47:00", "hhe101"));
        delayQueue.add(new DelayQueueExample("2018-06-08 00:46:00", "hhe102"));
        new Thread(new Runnable() {
            @Override
            public void run() {
                while (true) {
                    DelayQueueExample element = null;
                    try {
                        element = delayQueue.poll();
                        if (element == null) {
                            break;
                        } else {
                            System.out.println(element);
                        }
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            }
        }).start();


    }
}

源码部分:取值的逻辑相似

 public E poll() {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            E first = q.peek();
            if (first == null || first.getDelay(NANOSECONDS) > 0)//丢掉延迟大于0的队列值
                return null;
            else
                return q.poll();
        } finally {
            lock.unlock();
        }
    }

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