【java】java.util.Timer类学习

好几天没写了，今天看到一个问题是“sevlet中如何使用定时访问数据库”？
第一个反映就是crontab和quarts，but 其实JDK中提供了这样的工具Timer

public static void main(String[] args) throws SQLException {
  //DBUtil.getTableName("ted");
  Timer tr = new Timer();
  Calendar c2 = new GregorianCalendar(2010,Calendar.DECEMBER,20,15,13,00); 
  System.out.println(c2.getTime());
  tr.schedule(new task(), new Date(), 60*1000); //每隔60秒调度一次
}

public class task extends TimerTask{
	public void run() {
		System.out.println("开始执行自动关机操作...");
	}
}

schedule是定时调度method，look it's source code:

private TaskQueue queue = new TaskQueue();

public void schedule(TimerTask task, Date firstTime, long period) {
        if (period <= 0)
            throw new IllegalArgumentException("Non-positive period.");
        sched(task, firstTime.getTime(), -period);
    }

private void sched(TimerTask task, long time, long period) {
        if (time < 0)
            throw new IllegalArgumentException("Illegal execution time.");
        //此处的queue是TaskQueue类型，是innerClass，感觉有点Hashmap的Entry的思想吧，O(∩_∩)O~
        synchronized(queue) {
            if (!thread.newTasksMayBeScheduled)
                throw new IllegalStateException("Timer already cancelled.");

            synchronized(task.lock) {
                if (task.state != TimerTask.VIRGIN)
                    throw new IllegalStateException(
                        "Task already scheduled or cancelled");
                task.nextExecutionTime = time;
                task.period = period;
                task.state = TimerTask.SCHEDULED;
            }

            queue.add(task);
            if (queue.getMin() == task)
                queue.notify();
        }
    }

具体的逻辑不说了，看看schedule的第一个参数TimerTask task，其实TimerTask是一个抽象线程类，一定要实现run了。（PS：哥多线程是弱项啊）

public abstract class TimerTask implements Runnable