java自带定时任务功能(Timer&TimerTask)

java自带定时任务功能(Timer&TimerTask)

介绍

开发中我们经常会有这样的业务，比如在凌晨的时候跑一个任务或者指定在某个时刻跑任务，这就是所谓的定时任务。通常定时任务也是异步处理的，
此时我会联想到消息中间件的功能(异步与解耦),java自带了简单的定时任务功能，通过借助Timer和TimeTask可以时间简单的任务调度功能。

任务调度器的最核心两点
1、任务(定义具体干什么,通常实现Runnable接口)
2、调度器(定义何时如何调度任务)

java自带的简单任务调度无法满足企业开发应用，如果要实现比较复杂的任务调度那么就需要借助第三方组件比如Quartz。

通常实际开发我们会结合Quartz和Spring来达到我们任务调度的目的

Timer

java.util.Timer是一个实用工具类，该类用来调度一个线程，使它可以在将来某一时刻执行。 Java的Timer类可以调度一个任务运行一次，或定期运行。

说简单点Timer就是一个调度器。

/**
* @author xuyi3
* @2016年7月22日 @上午11:41:47
* @TimeTest
* @功能说明:<br>
* @春风十里不如你
* @备注
*/
public class TimerTest {

//TImer构造方法演示
public void testTimer() {

// Timer timer=new Timer();//无参构造器
// Timer timer=new Timer("timerName");//Creates a new timer whose
// associated thread has the specified name(给运行这个Timer的线程命名)
// Timer timer=new Timer(true);//指定运行这个Timer线程是否守护线程
// Timer timer=new Timer("timerName", false);//命令和指定线程类型

}

/**
* 凡是涉及到线程相关的内容学习,主要是在main方法里面跑,不要再Junit单元测试里面跑。
*
* @param args
*/
public static void main(String[] args) {

Timer timer = new Timer();
// 实际任务
SimpleTimeTask simpleTimeTask = new SimpleTimeTask();

// 延期时间
long delayTime = 5000;
// 执行周期
long periodTime = 3000;

/**
* delayTime毫秒后开始执行任务
*/
// timer.schedule(simpleTimeTask, delayTime);

/**
* delayTime毫秒之后开始执行任务,之后每隔periodTime执行一次。
*/
// timer.schedule(simpleTimeTask, delayTime,periodTime);

/**
* Schedules the specified task for execution at the specified time. If
* the time is in the past, the task is scheduled for immediate
* execution.
*
* 在指定时间执行任务,如果指定时间小于当前时间那么就立即执行
*
*/
// timer.schedule(simpleTimeTask, new Date(System.currentTimeMillis() -
// delayTime));

/**
* Schedules the specified task for repeated fixed-delay execution,
* beginning after the specified delay. Subsequent executions take place
* at approximately regular intervals separated by the specified period.
*
*
* 在指定的延时后执行任务,之后每隔periodTime毫秒重复执行。
*
* 和schedule(TimerTask task, long delay, long period)方法一样,只是策略有点不同
*
*/
// timer.schedule(simpleTimeTask, new Date(), periodTime);

// timer.scheduleAtFixedRate(simpleTimeTask, delayTime, periodTime);

/**
* Schedules the specified task for repeated fixed-rate execution,
* beginning at the specified time. Subsequent executions take place at
* approximately regular intervals, separated by the specified period.
*
* 在指定的时间执行任务,之后每隔periodTime毫秒重复执行。
*
* 和schedule(TimerTask task, Date firstTime, long period)方法一样,只是策略有点不同
*
*/
// timer.scheduleAtFixedRate(simpleTimeTask, new Date(), periodTime);

// 备注:策略(默认使用fixedDelay)
// fixedRate:定时间隔执行,不管上次任务是否已执行完毕
// fixedDelay:每次任务执行完毕之后delay固定的时间

}

}

TimerTask类介绍和使用

TimerTask抽象类表示定义任务类，具体的任务都要继承该抽象类，该抽象类厘米那最主要的方法就是run()抽象方法。

/**
* A task that can be scheduled for one-time or repeated execution by a Timer.
*
* @author  Josh Bloch
* @see     Timer
* @since   1.3
*/

public abstract class TimerTask implements Runnable {
/**
* This object is used to control access to the TimerTask internals.
*/
final Object lock = new Object();

/**
* The state of this task, chosen from the constants below.
*/
int state = VIRGIN;

/**
* This task has not yet been scheduled.
*/
static final int VIRGIN = 0;

/**
* This task is scheduled for execution.  If it is a non-repeating task,
* it has not yet been executed.
*/
static final int SCHEDULED   = 1;

/**
* This non-repeating task has already executed (or is currently
* executing) and has not been cancelled.
*/
static final int EXECUTED    = 2;

/**
* This task has been cancelled (with a call to TimerTask.cancel).
*/
static final int CANCELLED   = 3;

long nextExecutionTime;

/**
* Period in milliseconds for repeating tasks.  A positive value indicates
* fixed-rate execution.  A negative value indicates fixed-delay execution.
* A value of 0 indicates a non-repeating task.
*/
long period = 0;

/**
* The action to be performed by this timer task.
*/
public abstract void run();

/**
* Cancels this timer task.  If the task has been scheduled for one-time
* execution and has not yet run, or has not yet been scheduled, it will
* never run.  If the task has been scheduled for repeated execution, it
* will never run again.  (If the task is running when this call occurs,
* the task will run to completion, but will never run again.)
*/
public boolean cancel() {
synchronized(lock) {
boolean result = (state == SCHEDULED);
state = CANCELLED;
return result;
}
}

/**
* Returns the scheduled execution time of the most recent
* actual execution of this task.  (If this method is invoked
* while task execution is in progress, the return value is the scheduled
* execution time of the ongoing task execution.)
*/
public long scheduledExecutionTime() {
synchronized(lock) {
return (period < 0 ? nextExecutionTime + period
: nextExecutionTime - period);
}
}
}

总结

如果是简单的定时任务设置，则可以使用java自带的TImer和TimerTask来完成，如果比较复杂的推荐使用Quartz任务调度框架来完成。

参考