定时任务的实现方式

定时任务的实现有3种方式：①while死循环 ②linux crontab ③Java TimerTask

以后补充

③还有一种不精确的方法是TimerTask。

1         TimerTask task = new TimerTask() {
2             @Override
3             public void run() {
4                 //do something
5             }
6         };
7         Timer t = new Timer();
8         t.scheduleAtFixedRate(task, 60000, 60000);

对scheduleAtFixedRate方法的解释：Timer.class的源码是这样写的。

long delay是启动这个定时任务的延迟：System.currentTimeMillis()+delay；

long period是between successive task executions.成功执行后，过period时间，再次执行一次定时任务。

 1      /*
 2      * @param task   task to be scheduled.
 3      * @param delay  delay in milliseconds before task is to be executed.
 4      * @param period time in milliseconds between successive task executions.
 5      * @throws IllegalArgumentException if <tt>delay</tt> is negative, or
 6      *         <tt>delay + System.currentTimeMillis()</tt> is negative.
 7      * @throws IllegalStateException if task was already scheduled or
 8      *         cancelled, timer was cancelled, or timer thread terminated.
 9      */
10     public void scheduleAtFixedRate(TimerTask task, long delay, long period) {
11         if (delay < 0)
12             throw new IllegalArgumentException("Negative delay.");
13         if (period <= 0)
14             throw new IllegalArgumentException("Non-positive period.");
15         sched(task, System.currentTimeMillis()+delay, period);
16     }