The use of JAVA collection DelayQueue (synchronous timeout queue)

https://www.cnblogs.com/hhan/p/10678466.html
 
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article directories 
[a] Introduction 
[two] DelayQueue inheritance hierarchy
 1 . The core method 
the Take () 
PUT (E) 
the offer (E) 
poll () 
PEEK ( ) 
size () 
clear () 
[3] Use DelayQueue to 
prepare Delayed implementation class
 1. Constructor 
[1] Introduction 
An unbounded blocking queue 
from java api 
Delayed element can only extract elements from it when the delay expires. The head of the queue is the Delayed element with the longest retention time after the delay expires. If none of the delays have expired, the queue has no head and poll will return null . When an element's getDelay (TimeUnit.NANOSECONDS) method returns a value less than or equal to 0, an expiration occurs. Even if you cannot use take or poll to remove unexpired elements, they will not be treated as normal elements. For example, the size method returns the count of both expired and unexpired elements. Null elements are



      not allowed in this queue . 
[2] DelayQueue inheritance system public  classDelayQueue <E extends Delayed> extends AbstractQueue <E> implements BlockingQueue <E> 
1 
1. The core method 
take () 
gets and removes the head of this queue, and waits (if any) necessary). 

put (E) 
inserts the specified element into this delay queue. 

offer (E) 
inserts the specified element into this delay queue. 

poll () 
gets and removes the head of this queue, or returns null if this queue does not contain an element with an expired delay time . 

peek () 
gets but does not remove the head of this queue; if this queue is empty, it returns null . 

size () 
returns the number of elements in this collection. 

clear () 
automatically removes all elements of this delay queue. 

[Three] Use DelayQueue to 
prepare Delayed implementation class 
DelayQueue <E extends Delayed>Using this timeout queue, according to his generic restriction type, the element he stores must be a subclass of the Delayed interface; 
therefore we must first construct such a subclass, assuming there is a scheduled task Task, and then from the set time Take out the queue and execute him. 

Scheduled Task Task 

/ ** 
 * 
 * Scheduled Task 
 * / 
public  class Task { 

    // task id 
    private Integer id;
     // task name 
    private String name;
     // execution time 
    private Long time; 
    
    public Task (Integer id , String name, Long time) {
         this .id = id;
         this .name = name;
         this .time = time; 
    } 
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Long getTime() {
        return time;
    }
    public void setTime(Long time) {
        this.time = time;
    }
    @Override
    publicString toString () {
         return "Task [id =" + id + ", name =" + name + ", time =" + new Date (time) .toString () + "]" ; 
    } 
} 
 
 
Delayed implementation class: 
because We don't want to change the structure of Task, so create another implementation class TaskDelayed 

public  class TaskDelayed implements Delayed { 
    
    // task 
    private Task task; 
    
    public TaskDelayed (Task task) {
         super ();
         this .task = task; 
    } 
    
    public Task getTask ( ) {
         return task; 
    } 

    @Override 
    public  int compareTo(Delayed o) {
        return (int) (this.getDelay(TimeUnit.MILLISECONDS) - o.getDelay(TimeUnit.MILLISECONDS));
    }

    @Override
    public long getDelay(TimeUnit unit) {
        long time = task.getTime();
        long currentTime = System.currentTimeMillis();
        return unit.convert(time - currentTime, TimeUnit.MILLISECONDS);
    }
    
}
 
1. 构造方法
BlockingQueue<TaskDelayed> queue = new DelayQueue<>();
1
put 与 take (一直阻塞直到完成操作为止)

    public static void main(String[] args) throws InterruptedException {
        BlockingQueue<TaskDelayed> queue = new DelayQueue<>();
        queue.put(new TaskDelayed(new Task(5, "ssss", System.currentTimeMillis() + 9000L)));
        queue.put(new TaskDelayed(new Task(2, "ssss", System.currentTimeMillis() + 6000L)));
        queue.put(new TaskDelayed(new Task(3, "ssss", System.currentTimeMillis() + 7000L)));
        queue.put(new TaskDelayed(new Task(1, "ssss", System.currentTimeMillis() + 5000L)));
        queue.put(new TaskDelayed(new Task(4, "ssss", System.currentTimeMillis() + 8000L)));
        
        for(;;) {
            System.out.println(queue.take().getTask() + "----" + new Date());
        }
    }
 
执行结果

Task [id=1, name=ssss, time=Wed Jan 23 14:09:12 CST 2019]----Wed Jan 23 14:09:12 CST 2019
Task [id=2, name=ssss, time=Wed Jan 23 14:09:13 CST 2019]----Wed Jan 23 14:09:13 CST 2019
Task [id= 3, name = ssss, time = Wed Jan 23 14:09:14 CST 2019] ---- Wed Jan 23 14:09:14 CST 2019 
Task [id = 4, name = ssss, time = Wed Jan 23 14 : 09: 15 CST 2019] ---- Wed Jan 23 14:09:15 CST 2019 
Task [id = 5, name = ssss, time = Wed Jan 23 14:09:16 CST 2019] ---- Wed Jan 23 14:09:16 CST 2019
  
The time taken here is the same as the current system time, because we specified the time he took it out. The 

key method is Delayed 

public  interface Delayed extends Comparable <Delayed> { 

    long getDelay (TimeUnit unit); 
} 
 
Specific implementation: 
Returns the remaining delay time associated with this object, expressed in the given time unit. 

    @Override 
    public  long getDelay (TimeUnit unit) {
         long time = task.getTime ();
        long currentTime = System.currentTimeMillis ();
         return unit.convert (time- currentTime, TimeUnit.MILLISECONDS); 
    } 
 
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