Java Spring @Scheduled tasks executing twice

java spring schedule
KS1 picture KS1 · Jan 9, 2013 · Viewed 45.9k times · Source

I have a simple test method here that is set to run every 5 seconds and it does, but looking at the System.out you can see it appears to be doing something odd.

@Scheduled(cron="*/5 * * * * ?")
public void testScheduledMethod() {
     System.out.println(new Date()+" > Running testScheduledMethod...");
}

Output:

Wed Jan 09 16:49:15 GMT 2013 > Running testScheduledMethod...
Wed Jan 09 16:49:15 GMT 2013 > Running testScheduledMethod...
Wed Jan 09 16:49:20 GMT 2013 > Running testScheduledMethod...
Wed Jan 09 16:49:20 GMT 2013 > Running testScheduledMethod...
Wed Jan 09 16:49:25 GMT 2013 > Running testScheduledMethod...
Wed Jan 09 16:49:25 GMT 2013 > Running testScheduledMethod...
Wed Jan 09 16:49:30 GMT 2013 > Running testScheduledMethod...
Wed Jan 09 16:49:30 GMT 2013 > Running testScheduledMethod...

Why is it running TWICE (appear) each time?

Answer

nicholas.hauschild picture nicholas.hauschild · Jan 9, 2013

If you look at the documentation, there is a note that explicitly calls out this phenomenon.

The note is under section 25.5.1 at this link, and reads:

Make sure that you are not initializing multiple instances of the same @Scheduled annotation class at runtime, unless you do want to schedule callbacks to each such instance. Related to this, make sure that you do not use @Configurable on bean classes which are annotated with @Scheduled and registered as regular Spring beans with the container: You would get double initialization otherwise, once through the container and once through the @Configurable aspect, with the consequence of each @Scheduled method being invoked twice.

I understand that this is merely suggestion at this point, but I do not think we have enough information to diagnose the issue further.

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