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。

        TimerTask task = new TimerTask() {
            @Override
            public void run() {
                //do something
            }
        };
        Timer t = new Timer();
        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。

     /*
     * @param task   task to be scheduled.
     * @param delay  delay in milliseconds before task is to be executed.
     * @param period time in milliseconds between successive task executions.
     * @throws IllegalArgumentException if <tt>delay</tt> is negative, or
     *         <tt>delay + System.currentTimeMillis()</tt> is negative.
     * @throws IllegalStateException if task was already scheduled or
     *         cancelled, timer was cancelled, or timer thread terminated.
     */
    public void scheduleAtFixedRate(TimerTask task, long delay, long period) {
        if (delay < 0)
            throw new IllegalArgumentException("Negative delay.");
        if (period <= 0)
            throw new IllegalArgumentException("Non-positive period.");
        sched(task, System.currentTimeMillis()+delay, period);
    }