Run Java code once every hour

Question

I'm tryng to write a simple Java program that runs some code every hour when the minute hand is at 20. The issue is that that the way I'm doing it is incredibly CPU intensive. I'm familiar with Quartz but I'm looking for a much simpler solution, any ideas?

    boolean run = true;
    while(run){
        Calendar calendar = new GregorianCalendar();
        int minute = calendar.get(Calendar.MINUTE);
        if(minute == 20){
            //Do some Stuff             
        }
    }

Answer 1

A simple solution is to use the Executors framework:

final ScheduledExecutorService s = Executors.newSingleThreadScheduledExecutor();
s.scheduleAtFixedRate(task, secondsToFirstOccurence, 60*60, TimeUnit.SECONDS);

And use some logic to find out secondsToFirstOccurence. This will probably involve a Calendar instance, but would be much more convenient with JodaTime.

Answer 2

Be aware that if your application is running inside a managed environment (a web or ejb container) you're not allowed to use Thread.sleep() or any other thread-related operations, for that matter, take a look at the EJB restrictions page. I warn about this because the question is tagged java-ee, so the "simple application" might not be so simple after all - if it's running inside a Java EE container there are additional considerations to take care of.

If you're building an enterprise-grade application, forget about Thread.sleep(). Go for a full-fledged job scheduler, Use Quartz, it's an open source and extremely mature and reliable product. Or use Obsidian Scheduler, a feature-rich commercial scheduler with more out-of-the-box features than Quartz.

A lightweight alternative to a full-fledged scheduler (but suitable for running inside a container) would be to use the Timer service.