java自带定时任务功能(Timer&TimerTask)

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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

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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。

Timer使用

/** * @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    }}

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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。

代码

/** * 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);        }    }}

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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。

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参考

1、http://www.importnew.com/9978.html
2、http://www.cnblogs.com/dolphin0520/p/3938991.html