Java: How do I run function repeatedly every week Sunday at 12:01 AM?

Question

How can I run a function repeatedly every week Sunday at 12:01 AM while using minimal CPU during the downtime/off time? Thread.sleep()?

Answer 1

Use the @Scheduled annotation from Spring framework. The cron expression for every week Sunday at 12:01 AM is: 1 0 * * 0

    @Scheduled(cron="1 0 * * 0")
    public void doSomething() {
        // something that execute once a week
    }

Answer 2

import java.util.Calendar;
import java.util.Date;
import java.util.Locale;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

class SundayRunner implements Runnable
{

  private final Runnable target;

  private final ScheduledExecutorService worker;

  private volatile Date now;

  SundayRunner(Runnable target, ScheduledExecutorService worker) {
    this.target = target;
    this.worker = worker;
  }

  @Override
  public final void run()
  {
    if (now == null)
      now = new Date();
    else
      target.run();
    Date next = next(now);
    long delay = next.getTime() - now.getTime();
    now = next;
    worker.schedule(this, delay, TimeUnit.MILLISECONDS);
  }

  Date next(Date now)
  {
    Calendar cal = Calendar.getInstance(Locale.US);
    cal.setTime(now);
    cal.set(Calendar.DAY_OF_WEEK, Calendar.SUNDAY);
    cal.set(Calendar.HOUR_OF_DAY, 0);
    cal.set(Calendar.MINUTE, 1);
    cal.set(Calendar.SECOND, 0);
    cal.set(Calendar.MILLISECOND, 0);
    Date sunday;
    for (sunday = cal.getTime(); sunday.before(now); sunday = cal.getTime())
      cal.add(Calendar.DATE, 7);
    return sunday;
  }

  public static void main(String... argv)
  {
    ScheduledExecutorService worker = 
       Executors.newSingleThreadScheduledExecutor();
    Runnable job = new Runnable() {
      @Override
      public void run()
      {
        System.out.printf("The time is now %tc.%n", new Date());
      }
    };
    worker.submit(new SundayRunner(job, worker));
  }

}