4.5.6 DelayQueue簡單使用demo

支持延時獲取元素的無界阻塞隊列，隊列元素必須實現Delayed接口，在創建元素的時候可以指定多久才能從隊列中獲取當前元素。時間到了才能從隊列中獲取到元素

簡單使用

實體implements Delayed

public class MyDelayed implements Delayed {
    private String key;
    private long currentTime;
    private long expireTime;

    public MyDelayed(String key, long expireTime) {
        this.key=key;
        this.expireTime=expireTime;
        this.currentTime = System.currentTimeMillis();
    }

    public String getKey() {
        return key;
    }

    public void setKey(String key) {
        this.key = key;
    }

    /**
     * 獲取剩餘的時間
     * @param unit
     * @return
     */
    @Override
    public long getDelay(TimeUnit unit) {
        return expireTime - unit.MILLISECONDS.toSeconds(System.currentTimeMillis()-currentTime);
    }

    /**
     * 剩餘時間升序排列
     * @param o
     * @return
     */
    @Override
    public int compareTo(Delayed o) {
        MyDelayed p = (MyDelayed) o;
        if(this.getDelay(TimeUnit.MICROSECONDS) > p.getDelay(TimeUnit.MICROSECONDS))
            return 1;
        if(this.getDelay(TimeUnit.MICROSECONDS) > p.getDelay(TimeUnit.MICROSECONDS))
            return -1;
        return 0;
    }

    @Override
    public String toString() {
        return "MyDelayed{" +
                "key='" + key + '\'' +
                ", currentTime=" + currentTime +
                ", expireTime=" + expireTime +
                '}';
    }
}

測試

public class Test2 {
    public static void main(String[] args) throws InterruptedException {
        DelayQueue<MyDelayed> queue = new DelayQueue<>();
        queue.add(new MyDelayed("key1", 4));
        queue.add(new MyDelayed("key2", 3));
        queue.add(new MyDelayed("key3", 2));

        System.out.println("會一直阻塞，直到元素過期");
        System.out.println(queue.take());
        System.out.println(queue);
        System.out.println(queue.take());
        System.out.println(queue);
    }
}

結果：

MyDelayed{key='key1', currentTime=1593955613953, expireTime=4}
[MyDelayed{key='key3', currentTime=1593955613954, expireTime=2}, MyDelayed{key='key2', currentTime=1593955613953, expireTime=3}]
MyDelayed{key='key3', currentTime=1593955613954, expireTime=2}
[MyDelayed{key='key2', currentTime=1593955613953, expireTime=3}]