Question

From reading on Stack Overflow I’ve seen that many of you don’t recommend using Timer Task. Hmmm… but I already implemented this:

I have this code:

detectionHandlerTimer.schedule(myTimerTask, 60 * 1000, 60 * 1000);

The thing is that work of myTimerTask lasts some time.

I would like this behavior:

1. wait 60 sec.
2. do task for some time (e.g. 40 – 100 sec).
3. task finished.
4. wait 60 seconds.
5. do task for some time (e.g. 40 – 100 sec).

But the code above behaves like this

1. wait 60 sec.
2. do task for some time (e.g. 40 – 100 sec).
3. task finished
4. do task for some time (e.g. 40 – 100 sec).

Because the time duration of task is bigger than 60, timer starts task immediately after task is finished. But I would like it to wait again.

Answer 1

This works. The key is to have the task itself (after it completes) schedule the next occurrence of the task.

import java.util.Timer;
import java.util.TimerTask;

public class TaskManager {

    private Timer timer = new Timer();

    public static void main(String[] args) {
        TaskManager manager = new TaskManager();
        manager.startTask();
    }

    public void startTask() {
        timer.schedule(new PeriodicTask(), 0);
    }

    private class PeriodicTask extends TimerTask {
        @Override
        public void run() {
            System.out.println(System.currentTimeMillis() + " Running");

            /* replace with the actual task */
            try {
                Thread.sleep(15 * 1000);
            } catch(InterruptedException e) {
                e.printStackTrace();
            }
            /* end task processing */

            System.out.println(System.currentTimeMillis() + " Scheduling 10 seconds from now");
            timer.schedule(new PeriodicTask(), 10 * 1000);
        }
    }
}

Which prints:

$ javac TaskManager.java && java TaskManager
1288282514688 Running
1288282529711 Scheduling 10 seconds from now
1288282539712 Running
1288282554713 Scheduling 10 seconds from now
1288282564714 Running

Here’s what it looks like if you extract the second components of the timestamps (for clarity):

$ javac TaskManager.java && java TaskManager
14                                    Running
29 (+15 seconds execution)            Scheduling 10 seconds from now
39 (+10 seconds delay until next run) Running
54 (+15 seconds execution)            Scheduling 10 seconds from now
64 (+10 seconds delay until next run) Running

Just replace the 10s with 60s.