java定時任務接口ScheduledExecutorService

一、ScheduledExecutorService 設計思想

ScheduledExecutorService,是基於線程池設計的定時任務類,每個調度任務都會分配到線程池中的一個線程去執行,也就是說,任務是併發執行,互不影響。

需要注意,只有當調度任務來的時候,ScheduledExecutorService纔會真正啓動一個線程,其餘時間ScheduledExecutorService都是出於輪詢任務的狀態。

ScheduledExecutorService 中兩種最常用的調度方法 ScheduleAtFixedRate 和 ScheduleWithFixedDelay。

ScheduleAtFixedRate ：每次執行時間爲上一次任務開始起向後推一個時間間隔。ScheduleAtFixedRate 是基於固定時間間隔進行任務調度

ScheduleWithFixedDelay： 每次執行時間爲上一次任務結束起向後推一個時間間隔。ScheduleWithFixedDelay 取決於每次任務執行的時間長短，是基於不固定時間間隔進行任務調度。

二、示例

ScheduleAtFixedRate

1、任務

import java.util.Date;

class Task implements Runnable {

	private String taskName;

	Task(String taskName) {
		this.taskName = taskName;
	}

	@Override
	public void run() {
		System.out.println(taskName + " is running.Time:" + new Date());
	}
}

2、執行類

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

public class TaskMain {
	public static void main(String[] args) {
		// 創建線程池
		ScheduledExecutorService service = Executors.newScheduledThreadPool(10);
		// 初始延時時間
		long initialDelay = 3;
		// 任務執行間隔
		long period = 1;
		System.out.println("任務開始：" + new Date());
		// 從現在開始3秒鐘之後，每隔1秒鐘執行一次Task1
		service.scheduleAtFixedRate(new Task("Task1"), initialDelay, period, TimeUnit.SECONDS);
	}
}

3、執行結果

任務開始：Sun Jan 27 16:24:30 CST 2019
Task1 is running.Time:Sun Jan 27 16:24:33 CST 2019
Task1 is running.Time:Sun Jan 27 16:24:34 CST 2019
Task1 is running.Time:Sun Jan 27 16:24:35 CST 2019
Task1 is running.Time:Sun Jan 27 16:24:36 CST 2019
Task1 is running.Time:Sun Jan 27 16:24:37 CST 2019
Task1 is running.Time:Sun Jan 27 16:24:38 CST 2019

ScheduleWithFixedDelay

1、任務

package com.learn.schedule;

import java.util.Date;

class Task implements Runnable {

	private String taskName;

	Task(String taskName) {
		this.taskName = taskName;
	}

	@Override
	public void run() {
		try {
			// 模擬業務執行1s
			Thread.sleep(1000L);
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
		System.out.println(taskName + " is running.Time:" + new Date());
	}
}

2、執行類

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

public class TaskMain {
	public static void main(String[] args) {
		// 創建線程池
		ScheduledExecutorService service = Executors.newScheduledThreadPool(10);
		// 初始延時時間
		long initialDelay = 3;
		// 任務執行間隔
		long period = 1;
		System.out.println("任務開始：" + new Date());

		// 從現在開始3秒鐘之後，每隔2秒鐘執行一次Task2
		service.scheduleWithFixedDelay(new Task("Task2"), initialDelay, period, TimeUnit.SECONDS);
	}
}

3、執行結果

任務開始：Sun Jan 27 16:29:52 CST 2019
Task2 is running.Time:Sun Jan 27 16:29:56 CST 2019
Task2 is running.Time:Sun Jan 27 16:29:58 CST 2019
Task2 is running.Time:Sun Jan 27 16:30:00 CST 2019
Task2 is running.Time:Sun Jan 27 16:30:02 CST 2019
Task2 is running.Time:Sun Jan 27 16:30:04 CST 2019
Task2 is running.Time:Sun Jan 27 16:30:06 CST 2019
Task2 is running.Time:Sun Jan 27 16:30:08 CST 2019
Task2 is running.Time:Sun Jan 27 16:30:10 CST 2019
Task2 is running.Time:Sun Jan 27 16:30:12 CST 2019
Task2 is running.Time:Sun Jan 27 16:30:14 CST 2019