Java定时器Timer简述

概述

主要用于Java线程里指定时间或周期运行任务。Timer是线程安全的，但不提供实时性(real-time)保证。

构造函数

Timer()

默认构造函数。

Timer(boolean)

指定关联线程是否作为daemon线程。

Timer(String)

指定关联线程的名称。

Timer(String, boolean)

同时指定关联线程的名称和是否作为daemon。

schdule方法

schedule(TimerTask task, long delay)

以当前时间为基准，延迟指定的毫秒后执行一次TimerTask任务。

schedule(TimerTask task, Date time)

在指定的日期执行一次TimerTask任务。

如果日期time早于当前时间，则立刻执行。

使用示例

public class Demo {
    private static Timer timer = new Timer();

    public static class MyTask extends TimerTask {
        @Override
        public void run() {
            System.out.println("Run Time：" + new Date().toString());
        }
    }

    public static void main(String[] args) {
        try {
            MyTask task = new MyTask();
            SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
            String dateStr = "2016-12-27 14:36:00";
            Date date = sdf.parse(dateStr);
            System.out.println("Date = " + date.toString() + " NowTime = " + new Date().toString());
            timer.schedule(task, date);
        } catch (ParseException e) {
            e.printStackTrace();
        }
    }
}

执行结果

Date = Tue Dec 27 14:36:00 CST 2016 NowTime = Tue Dec 27 21:28:04 CST 2016

Run Time：Tue Dec 27 21:28:04 CST 2016

说明是立刻执行。

schedule(TimerTask task, long delay, long period)

以当前时间为基准，延迟指定的毫秒后，再按指定的时间间隔地无限次数的执行TimerTask任务。(fixed-delay execution)

使用示例

public class Demo {
    private static Timer timer = new Timer();

    public static class MyTask extends TimerTask {
        @Override
        public void run() {
            System.out.println("Run Time: " + new Date().toString());
        }
    }

    public static void main(String[] args) {
        MyTask task = new MyTask();
        System.out.println("Now Time: " + new Date().toString());
        timer.schedule(task, 3000, 5000);
    }
}

执行结果

Now Time: Tue Dec 27 21:34:59 CST 2016

Run Time: Tue Dec 27 21:35:02 CST 2016

Run Time: Tue Dec 27 21:35:07 CST 2016

Run Time: Tue Dec 27 21:35:12 CST 2016

Run Time: Tue Dec 27 21:35:17 CST 2016

说明以当前基准时间延迟3秒后执行一次，以后按指定间隔时间5秒无限次数的执行。

schedule(TimerTask task, Date firstTime, long period)

在指定的日期之后，按指定的时间间隔地无限次数的执行TimerTask任务。(fixed-delay execution)

如果日期firstTime早于当前时间，则立刻执行，且不执行在时间差内的任务。

使用示例

public class Demo {
    private static Timer timer = new Timer();

    public static class MyTask extends TimerTask {
        @Override
        public void run() {
            System.out.println("Run Time：" + new Date().toString());
        }

        public static void main(String[] args) {
            try {
                MyTask task = new MyTask();
                SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
                String dateStr = "2016-12-27 14:36:00";
                Date date = sdf.parse(dateStr);
                System.out.println("Date = " + date.toString() + " NowTime = " + new Date().toString());
                timer.schedule(task, date, 3000);
            } catch (ParseException e) {
                e.printStackTrace();
            }
        }
    }
}

执行结果

Date = Tue Dec 27 14:36:00 CST 2016 NowTime = Tue Dec 27 21:43:30 CST 2016

Run Time：Tue Dec 27 21:43:30 CST 2016

Run Time：Tue Dec 27 21:43:33 CST 2016

Run Time：Tue Dec 27 21:43:36 CST 2016

说明指定的之间早于当前时间，则立刻执行，不会补充时间差内的任务。

scheduleAtFixedRate方法

scheduleAtFixedRate(TimerTask task, long delay, long period)

以当前时间为基准，延迟指定的毫秒后，再按指定的时间间隔周期性地无限次数的执行TimerTask任务。(fixed-rate execution)

使用示例

public class Demo {
    private static Timer timer = new Timer();

    public static class MyTask extends TimerTask {
        @Override
        public void run() {
            System.out.println("Run Time: " + new Date().toString());
        }
    }

    public static void main(String[] args) {
        MyTask task = new MyTask();
        System.out.println("Now Time: " + new Date().toString());
        timer.scheduleAtFixedRate(task, 3000, 5000);
    }
}

执行结果

Now Time: Tue Dec 27 21:58:03 CST 2016

Run Time: Tue Dec 27 21:58:06 CST 2016

Run Time: Tue Dec 27 21:58:11 CST 2016

Run Time: Tue Dec 27 21:58:16 CST 2016

Run Time: Tue Dec 27 21:58:21 CST 2016

说明以当前基准时间延迟3秒后执行一次，以后按指定间隔时间5秒无限次数的执行。

scheduleAtFixedRate(TimerTask task, Date firstTime, long period)

在指定的日期之后，按指定的时间间隔周期性地无限次数的执行TimerTask任务。(fixed-rate execution)

如果日期firstTime早于当前时间，则立即执行，并补充性的执行在时间差内的任务。

使用示例

public class Demo {
    private static Timer timer = new Timer();

    public static class MyTask extends TimerTask {
        @Override
        public void run() {
            System.out.println("Run Time：" + new Date().toString());
        }

        public static void main(String[] args) {
            try {
                MyTask task = new MyTask();
                SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
                String dateStr = "2016-12-27 22:02:00";
                Date date = sdf.parse(dateStr);
                System.out.println("Date = " + date.toString() + " NowTime = " + new Date().toString());
                timer.scheduleAtFixedRate(task, date, 5000);
            } catch (ParseException e) {
                e.printStackTrace();
            }
        }
    }
}

执行结果

Date = Tue Dec 27 22:02:00 CST 2016 NowTime = Tue Dec 27 22:02:54 CST 2016

Run Time：Tue Dec 27 22:02:54 CST 2016

Run Time：Tue Dec 27 22:02:54 CST 2016

Run Time：Tue Dec 27 22:02:54 CST 2016

Run Time：Tue Dec 27 22:02:54 CST 2016

Run Time：Tue Dec 27 22:02:54 CST 2016

Run Time：Tue Dec 27 22:02:54 CST 2016

Run Time：Tue Dec 27 22:02:54 CST 2016

Run Time：Tue Dec 27 22:02:54 CST 2016

Run Time：Tue Dec 27 22:02:54 CST 2016

Run Time：Tue Dec 27 22:02:54 CST 2016

Run Time：Tue Dec 27 22:02:54 CST 2016

Run Time：Tue Dec 27 22:02:55 CST 2016

Run Time：Tue Dec 27 22:03:00 CST 2016

Run Time：Tue Dec 27 22:03:05 CST 2016

说明指定的之间早于当前时间，则立刻执行。

在时间22:02:00--22:02:54内大约有11个5秒间隔，则优先补充性的执行在时间差内的任务，然后在22:02:55补充完毕(执行12次。ps：0-55秒区间段内首位都算上，正好触发12次)，此后每隔5秒执行一次定时任务。

执行任务延时对比之 schedule 和 scheduleAtFixedRate

schedule不延时

使用示例

public class Demo {
    private static Timer timer = new Timer();
    private static int runCount = 0;

    public static class MyTask extends TimerTask {
        @Override
        public void run() {
            try {
                System.out.println("Begin Run Time: " + new Date().toString());
                Thread.sleep(3000);
                System.out.println("End Run Time: " + new Date().toString());
                runCount++;
                if (runCount == 3) {
                    timer.cancel();
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

        }
    }

    public static void main(String[] args) {
        try {
            MyTask task = new MyTask();
            SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
            String dateStr = "2016-12-27 14:36:00";
            Date date = sdf.parse(dateStr);
            System.out.println("Date = " + date.toString() + " NowTime = " + new Date().toString());
            timer.schedule(task, date, 5000);
        } catch (ParseException e) {
            e.printStackTrace();
        }
    }
}

执行结果

早于当前基准时间

Date = Tue Dec 27 14:36:00 CST 2016 NowTime = Tue Dec 27 22:23:37 CST 2016

Begin Run Time: Tue Dec 27 22:23:37 CST 2016

End Run Time: Tue Dec 27 22:23:40 CST 2016

Begin Run Time: Tue Dec 27 22:23:42 CST 2016

End Run Time: Tue Dec 27 22:23:45 CST 2016

Begin Run Time: Tue Dec 27 22:23:47 CST 2016

End Run Time: Tue Dec 27 22:23:50 CST 2016

Process finished with exit code 0

晚于当前基准时间

Date = Tue Dec 27 22:42:00 CST 2016 NowTime = Tue Dec 27 22:41:54 CST 2016

Begin Run Time: Tue Dec 27 22:42:00 CST 2016

End Run Time: Tue Dec 27 22:42:03 CST 2016

Begin Run Time: Tue Dec 27 22:42:05 CST 2016

End Run Time: Tue Dec 27 22:42:08 CST 2016

Begin Run Time: Tue Dec 27 22:42:10 CST 2016

End Run Time: Tue Dec 27 22:42:13 CST 2016

Process finished with exit code 0

不管早还是晚于基准时间，都不进行补偿，下一次任务的执行时间参考的是上一次任务的开始时间点来计算。

schedule延时

使用示例

public class Demo {
    private static Timer timer = new Timer();
    private static int runCount = 0;

    public static class MyTask extends TimerTask {
        @Override
        public void run() {
            try {
                System.out.println("Begin Run Time: " + new Date().toString());
                Thread.sleep(5000);
                System.out.println("End Run Time: " + new Date().toString());
                runCount++;
                if (runCount == 3) {
                    timer.cancel();
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

        }
    }

    public static void main(String[] args) {
        try {
            MyTask task = new MyTask();
            SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
            String dateStr = "2016-12-27 22:42:00";
            Date date = sdf.parse(dateStr);
            System.out.println("Date = " + date.toString() + " NowTime = " + new Date().toString());
            timer.schedule(task, date, 3000);
        } catch (ParseException e) {
            e.printStackTrace();
        }
    }
}

执行结果

早于当前基准时间

Date = Tue Dec 27 22:42:00 CST 2016 NowTime = Tue Dec 27 22:45:17 CST 2016

Begin Run Time: Tue Dec 27 22:45:17 CST 2016

End Run Time: Tue Dec 27 22:45:22 CST 2016

Begin Run Time: Tue Dec 27 22:45:22 CST 2016

End Run Time: Tue Dec 27 22:45:27 CST 2016

Begin Run Time: Tue Dec 27 22:45:27 CST 2016

End Run Time: Tue Dec 27 22:45:32 CST 2016

Process finished with exit code 0

晚于当前基准时间

Date = Tue Dec 27 22:47:00 CST 2016 NowTime = Tue Dec 27 22:46:27 CST 2016

Begin Run Time: Tue Dec 27 22:47:00 CST 2016

End Run Time: Tue Dec 27 22:47:05 CST 2016

Begin Run Time: Tue Dec 27 22:47:05 CST 2016

End Run Time: Tue Dec 27 22:47:10 CST 2016

Begin Run Time: Tue Dec 27 22:47:10 CST 2016

End Run Time: Tue Dec 27 22:47:15 CST 2016

Process finished with exit code 0

不管早还是晚于当前基准时间，都不进行补偿，下一次任务的执行时间都是参考上一次任务结束的时间点来计算。

scheduleAtFixedRate不延时

使用示例

public class Demo {
    private static Timer timer = new Timer();
    private static int runCount = 0;

    public static class MyTask extends TimerTask {
        @Override
        public void run() {
            try {
                System.out.println("Begin Run Time: " + new Date().toString());
                Thread.sleep(3000);
                System.out.println("End Run Time: " + new Date().toString());
                runCount++;
                if (runCount == 1000) {
                    timer.cancel();
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    public static void main(String[] args) {
        try {
            MyTask task = new MyTask();
            SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
            String dateStr = "2016-12-27 22:51:42";
            Date date = sdf.parse(dateStr);
            System.out.println("Date = " + date.toString() + " NowTime = " + new Date().toString());
            timer.scheduleAtFixedRate(task, date, 5000);
        } catch (ParseException e) {
            e.printStackTrace();
        }
    }
}

执行结果

早于当前基准时间

Date = Tue Dec 27 22:51:42 CST 2016 NowTime = Tue Dec 27 22:51:57 CST 2016

Begin Run Time: Tue Dec 27 22:51:57 CST 2016

End Run Time: Tue Dec 27 22:52:00 CST 2016

Begin Run Time: Tue Dec 27 22:52:00 CST 2016

End Run Time: Tue Dec 27 22:52:03 CST 2016

Begin Run Time: Tue Dec 27 22:52:03 CST 2016

End Run Time: Tue Dec 27 22:52:06 CST 2016

Begin Run Time: Tue Dec 27 22:52:06 CST 2016

End Run Time: Tue Dec 27 22:52:09 CST 2016

Begin Run Time: Tue Dec 27 22:52:09 CST 2016

End Run Time: Tue Dec 27 22:52:12 CST 2016

Begin Run Time: Tue Dec 27 22:52:12 CST 2016

End Run Time: Tue Dec 27 22:52:15 CST 2016

Begin Run Time: Tue Dec 27 22:52:15 CST 2016

End Run Time: Tue Dec 27 22:52:18 CST 2016

Begin Run Time: Tue Dec 27 22:52:18 CST 2016

End Run Time: Tue Dec 27 22:52:21 CST 2016

Begin Run Time: Tue Dec 27 22:52:22 CST 2016

End Run Time: Tue Dec 27 22:52:25 CST 2016

Begin Run Time: Tue Dec 27 22:52:27 CST 2016

End Run Time: Tue Dec 27 22:52:30 CST 2016

Begin Run Time: Tue Dec 27 22:52:32 CST 2016

End Run Time: Tue Dec 27 22:52:35 CST 2016

Begin Run Time: Tue Dec 27 22:52:37 CST 2016

End Run Time: Tue Dec 27 22:52:40 CST 2016

Begin Run Time: Tue Dec 27 22:52:42 CST 2016

End Run Time: Tue Dec 27 22:52:45 CST 2016

Begin Run Time: Tue Dec 27 22:52:47 CST 2016

End Run Time: Tue Dec 27 22:52:50 CST 2016

Begin Run Time: Tue Dec 27 22:52:52 CST 2016

End Run Time: Tue Dec 27 22:52:55 CST 2016

Begin Run Time: Tue Dec 27 22:52:57 CST 2016

End Run Time: Tue Dec 27 22:53:00 CST 2016

Process finished with exit code 0

晚于当前基准时间

Date = Tue Dec 27 22:37:00 CST 2016 NowTime = Tue Dec 27 22:36:06 CST 2016

Begin Run Time: Tue Dec 27 22:37:00 CST 2016

End Run Time: Tue Dec 27 22:37:03 CST 2016

Begin Run Time: Tue Dec 27 22:37:05 CST 2016

End Run Time: Tue Dec 27 22:37:08 CST 2016

Begin Run Time: Tue Dec 27 22:37:10 CST 2016

End Run Time: Tue Dec 27 22:37:13 CST 2016

Process finished with exit code 0

不延时的情况下，当早于基准时间时，时间差内的执行任务未补偿完时，下一次执行任务的时间参考的是上一次执行任务的结束时间；一旦补偿完毕（注意粗体时间点），下一次执行任务的时间参考的是上一次执行任务的开始时间；当晚于基准时间时，下一次执行任务的时间参考的是上一次执行任务的开始时间。

scheduleAtFixedRate延时

使用示例

public class Demo {
    private static Timer timer = new Timer();
    private static int runCount = 0;

    public static class MyTask extends TimerTask {
        @Override
        public void run() {
            try {
                System.out.println("Begin Run Time: " + new Date().toString());
                Thread.sleep(5000);
                System.out.println("End Run Time: " + new Date().toString());
                runCount++;
                if (runCount == 3) {
                    timer.cancel();
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

        }
    }

    public static void main(String[] args) {
        try {
            MyTask task = new MyTask();
            SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
            String dateStr = "2016-12-27 22:28:00";
            Date date = sdf.parse(dateStr);
            System.out.println("Date = " + date.toString() + " NowTime = " + new Date().toString());
            timer.scheduleAtFixedRate(task, date, 3000);
        } catch (ParseException e) {
            e.printStackTrace();
        }
    }
}

执行结果

早于当前基准时间

Date = Tue Dec 27 23:01:00 CST 2016 NowTime = Tue Dec 27 23:01:19 CST 2016

Begin Run Time: Tue Dec 27 23:01:19 CST 2016

End Run Time: Tue Dec 27 23:01:24 CST 2016

Begin Run Time: Tue Dec 27 23:01:24 CST 2016

End Run Time: Tue Dec 27 23:01:29 CST 2016

Begin Run Time: Tue Dec 27 23:01:29 CST 2016

End Run Time: Tue Dec 27 23:01:34 CST 2016

Begin Run Time: Tue Dec 27 23:01:34 CST 2016

End Run Time: Tue Dec 27 23:01:39 CST 2016

晚于当前基准时间

Date = Tue Dec 27 22:28:00 CST 2016 NowTime = Tue Dec 27 22:27:55 CST 2016

Begin Run Time: Tue Dec 27 22:28:00 CST 2016

End Run Time: Tue Dec 27 22:28:05 CST 2016

Begin Run Time: Tue Dec 27 22:28:05 CST 2016

End Run Time: Tue Dec 27 22:28:10 CST 2016

Begin Run Time: Tue Dec 27 22:28:10 CST 2016

End Run Time: Tue Dec 27 22:28:15 CST 2016

Process finished with exit code 0

延时的情况下，即使是早于基准时间，由于延时效应，根本不可能补偿完毕时间差内的执行任务，故而在延时的情况下，下一次任务的执行时间都是参考上一次任务结束的时间来计算。

对比总结

	执行任务不延时	执行任务延时
早于当前基准时间	schedule：下一次任务的执行时间参考的是上一次任务的开始时间来计算。 scheduleAtFixedRate：当早于基准时间时，时间差内的执行任务未补偿完时，下一次执行任务的时间参考的是上一次任务的结束时间；一旦补偿完毕，下一次执行任务的时间参考上一次任务的开始时间来计算。	二者一样。下一次任务的执行时间都是参考上一次任务的结束时间来计算。
晚于当前基准时间	二者一样。下一次任务的执行时间参考的是上一次任务的开始时间来计算。	二者一样。下一次任务的执行时间都是参考上一次任务的结束时间来计算。

注意：scheduleAtFixedRate示例中firstTime是有区别的，而结果证明是有补偿性操作的。

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