DelayQueue队列研究

 

1.DelayQueue

是一个无界的BlockingQueue，用于放置实现了Delayed接口的对象，其中的对象只能在其到期时才能从队列中取走。这种队列是有序的，即队头对象的延迟到期时间最长。注意：不能将null元素放置到这种队列中。

 

 

 

2.Delayed

 

一种混合风格的接口，用来标记那些应该在给定延迟时间之后执行的对象。

此接口的实现必须定义一个 compareTo 方法，该方法提供与此接口的 getDelay 方法一致的排序。

 

 

3.DelayQueue队列中保存的是实现了Delayed接口的实现类，里面必须实现getDelay()和compareTo()方法，前者用于取DelayQueue里面的元素时判断是否到了延时时间，否则不予获取，是则获取。  compareTo()方法用于进行队列内部的排序

   getDelay(TimeUnit unit){

return unit.convert(time - now(),TimeUnit.NANOSECONDES);//time为设定的间隔时间

}

   compareTo(Object object){

 

if(object instanceof SchuduledTask){

SchuduledTask task = (SchuduledTask) object ;

                long l = this.time - task.time;

if(l > 0) return 1 ; //比当前的小则返回1，比当前的大则返回-1，否则为0

                else if(l < 0 ) return -1;

else return 0;

}

}

 

 

 

 

4.example示例

 

Student类:用于实现delayed接口的对象，继承并实现二个方法

package org.taobao.terminator.client.fww; import java.util.concurrent.Delayed; import java.util.concurrent.ExecutorService; import java.util.concurrent.TimeUnit; class Student implements Runnable,Delayed{ private String name; private long submitTime;//交卷时间 private long workTime;//考试时间 public Student() { } public Student(String name, long submitTime) { super(); this.name = name; workTime = submitTime; //都转为转为ns this.submitTime = TimeUnit.NANOSECONDS.convert(submitTime, TimeUnit.MILLISECONDS) + System.nanoTime(); } @Override public void run() { System.out.println(name + " 交卷,用时" + workTime/100 + "分钟"); } @Override public long getDelay(TimeUnit unit) { return unit.convert(submitTime - System.nanoTime(), unit.NANOSECONDS); } @Override public int compareTo(Delayed o) { Student that = (Student) o; return submitTime > that.submitTime?1:(submitTime < that.submitTime ? -1 : 0); } public static class EndExam extends Student{ private ExecutorService exec; public EndExam(int submitTime,ExecutorService exec) { super(null,submitTime); this.exec = exec; } @Override public void run() { exec.shutdownNow(); } } }  

 

Teacher类：辅助类

package org.taobao.terminator.client.fww; import java.util.concurrent.DelayQueue; import java.util.concurrent.ExecutorService; class Teacher implements Runnable{ private DelayQueue<Student> students; private ExecutorService exec; public Teacher(DelayQueue<Student> students,ExecutorService exec) { super(); this.students = students; this.exec = exec; } @Override public void run() { try { System.out.println("考试开始……"); while (!Thread.interrupted()) { students.take().run(); } System.out.println("考试结束……"); } catch (InterruptedException e) { e.printStackTrace(); } } }  

 

 

 

Exam类：执行测试类

package org.taobao.terminator.client.fww; import java.util.Random; import java.util.concurrent.DelayQueue; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; public class Exam { static final int STUDENT_SIZE = 45; public static void main(String[] args) { Random r = new Random(); DelayQueue<Student> students = new DelayQueue<Student>(); ExecutorService exec = Executors.newCachedThreadPool(); for(int i = 0; i < STUDENT_SIZE; i++){ students.put(new Student("学生" + ( i + 1), 3000 + r.nextInt(9000))); } students.put(new Student.EndExam(12000,exec));//1200为考试结束时间 exec.execute(new Teacher(students, exec)); } }  

 

5.参考资料

http://www.cnblogs.com/jobs/archive/2007/04/27/730255.html

DelayQueue比较直接的一个应用是，实现一个最简单的缓存