• 在Executor中延時執(zhí)行任務

• 在Executor中周期的執(zhí)行任務

ScheduledExecutorService類顧名思義，就是可以延遲執(zhí)行的Executor。如果，對于某些任務，我們并不想馬上執(zhí)行，而是想讓任務過一段時間后才執(zhí)行，或者讓任務進行周期性執(zhí)行。我們就可以采用ScheduledExecutorService類。

在Executor中延時執(zhí)行任務

Task類

package ScheduledThreadPoolExecutor;

import java.util.Date;
import java.util.concurrent.Callable;

public class Task implements Callable<String> {
    private String name;
    
    public Task(String name) {
        this.name = name;
    }

    @Override
    public String call() throws Exception {
        System.out.println(name + "starting at : " + new Date());
        return "Hello world!!!!";
    }
}

Main類：

package ScheduledThreadPoolExecutor;

import java.util.Date;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

public class Main {

    public static void main(String[] args) {
        
        ScheduledExecutorService executor =  Executors.newScheduledThreadPool(1);
        
        System.out.println("Main : starting at " + new Date());
        
        for(int i=0;i<5;i++) {
            Task task = new Task("Task" + i);
            executor.schedule(task, (i+1), TimeUnit.SECONDS);
        }
        
        executor.shutdown();
        
        try {
            executor.awaitTermination(1, TimeUnit.DAYS);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        
        System.out.println("Main end at :" + new Date());
    }

}

運行結果

Main : starting at Tue Jul 25 09:25:38 CST 2017
Task0starting at : Tue Jul 25 09:25:39 CST 2017
Task1starting at : Tue Jul 25 09:25:40 CST 2017
Task2starting at : Tue Jul 25 09:25:41 CST 2017
Task3starting at : Tue Jul 25 09:25:42 CST 2017
Task4starting at : Tue Jul 25 09:25:43 CST 2017
Main end at :Tue Jul 25 09:25:43 CST 2017

在Executor中周期的執(zhí)行任務

Executor框架通過并發(fā)任務而避免了線程的創(chuàng)建操作。當發(fā)送一個任務給Executor后，根據(jù)Executor的配置，它將盡快執(zhí)行這個任務。當任務結束之后，這個任務就會從Executor中刪除，如果想要再次執(zhí)行這個任務，就需要再次將這個任務發(fā)送給Executor。
Executor框架中，提供了ScheduledThreadPoolExecutor來提供任務的周期性執(zhí)行的功能

Task類：

package ScheduledThreadCycle;

import java.util.Date;
import java.util.concurrent.Callable;

public class Task implements Runnable {

    private String name;
    
    public Task(String name) {
        this.name = name;
    }

    @Override
    public void run() {
        
        System.out.println(name + " : Starting at : " + new Date());
        
    }

}

Main類：

package ScheduledThreadCycle;

import java.util.Date;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.TimeUnit;

public class Main {

    public static void main(String[] args) throws InterruptedException {
        
        ScheduledExecutorService executor = Executors.newScheduledThreadPool(1);
        
        System.out.println("Main start at :" + new Date());
        
        Task task = new Task("task");
        
        ScheduledFuture<?> result = executor.scheduleAtFixedRate(task, 1, 2, TimeUnit.SECONDS);
        
        for(int i=0;i<10;i++) {
            System.out.println("Main: Delay: " + result.getDelay(TimeUnit.MILLISECONDS));
            
            TimeUnit.MILLISECONDS.sleep(500);
        }
        
        //executor.shutdown();
        
        TimeUnit.SECONDS.sleep(5);
        
        System.out.println("Main : finished at : " + new Date());
        
        executor.shutdown();
    }

}

運行結果：

Main start at :Tue Jul 25 09:35:05 CST 2017
Main: Delay: 999
Main: Delay: 499
Main: Delay: -1
task : Starting at : Tue Jul 25 09:35:06 CST 2017
Main: Delay: 1498
Main: Delay: 998
Main: Delay: 497
task : Starting at : Tue Jul 25 09:35:08 CST 2017
Main: Delay: 1997
Main: Delay: 1497
Main: Delay: 996
Main: Delay: 453
task : Starting at : Tue Jul 25 09:35:10 CST 2017
task : Starting at : Tue Jul 25 09:35:12 CST 2017
task : Starting at : Tue Jul 25 09:35:14 CST 2017
Main : finished at : Tue Jul 25 09:35:15 CST 2017

想要通過Executor來執(zhí)行宇哥周期性的任務時，需要一個ScheduledExecutorService類，可以利用Executors工廠類創(chuàng)建ScheduledExecutorService類。
要創(chuàng)建周期性任務的Executor，就需要像ScheduledExecutorService這個執(zhí)行器發(fā)送周期性的任務，調(diào)用 scheduleAtFixedRate方法發(fā)送任務，值得注意的是這個方法，只接受runnable對象，不接收Callable對象。后面兩個參數(shù)分別指定第一次執(zhí)行的延遲時間，兩次執(zhí)行的時間周期。時間周期指的是兩次執(zhí)行開始的時間間隔。
scheduleAtFixedRate方法會返回宇哥ScheduledFuture對象，這個對象擴展自Future接口，這是一個參數(shù)化的類型接口，必須指定類型，由于任務是Runnable對象，沒有返回值，所以需要指定為<?>。