How to schedule task for start of every hour

Question

I'm developing a service that suppose to start of every hour repeating exactly on the hour (1:00PM, 2:00PM, 3:00PM, etc.).

I tried following but it has one problem that for first time i have to run the program exactly at start of hour and then this scheduler will repeat it.

ScheduledExecutorService scheduler = Executors.newSingleThreadScheduledExecutor();
scheduler.scheduleWithFixedDelay(new MyTask(), 0, 1, TimeUnit.HOURS);

Any suggestion to repeat my task regardless when i run the program?

Regards, Imran

Answer 1

I would also suggest Quartz for this. But the above code can be made to run first at the start of the hour using the initialDelay parameter.

Calendar calendar = Calendar.getInstance();
ScheduledExecutorService scheduler = Executors.newSingleThreadScheduledExecutor();
scheduler.scheduleAtFixedRate(new MyTask(), millisToNextHour(calendar), 60*60*1000, TimeUnit.MILLISECONDS);



private static long millisToNextHour(Calendar calendar) {
    int minutes = calendar.get(Calendar.MINUTE);
    int seconds = calendar.get(Calendar.SECOND);
    int millis = calendar.get(Calendar.MILLISECOND);
    int minutesToNextHour = 60 - minutes;
    int secondsToNextHour = 60 - seconds;
    int millisToNextHour = 1000 - millis;
    return minutesToNextHour*60*1000 + secondsToNextHour*1000 + millisToNextHour;
}