Spring @Scheduled annotation random delay

问题:

I am using the @Scheduled annotation from Spring framework to invoke a method. But I have multiple nodes in my setup and I do not want them to all run at exactly the same time. So I'd like to set a random value to the initial delay to offset them from each other.

import org.springframework.scheduling.annotation.Scheduled;

@Scheduled(fixedRate = 600000, initialDelay = <random number between 0 and 10 minutes> )

Unfortunately, I am only allowed to use a constant expression here. Is there any other way around this? I thought of using Spring expression language.

回答1:

You can configure the initialDelay through Spring Expression Language:

@Scheduled(fixedRate = 600000, initialDelayString = "#{ T(java.util.concurrent.ThreadLocalRandom).current().nextInt(10*60*1000) }" )

I don't have an IDE to test that code right now, so you may need to adapt that a bit.

回答2:

To make the initial delay randomly somewhere between 0 and the fixedRate try this:

@Scheduled(fixedDelayString = "${some.delay}", initialDelayString = "${random.int(${some.delay})}")

Where you define some.delay (but pick a more suitable name) as 10 minutes as a property like so in your application.properties or equivalent.

some.delay = 600000

Of course if you want to be lazy and hard code it you can always just use ${random.int(600000)}

回答3:

In this working example, the random delay will be between 5 and 10 seconds.

@Scheduled(fixedDelayString = "#{new Double((T(java.lang.Math).random() + 1) * 5000).intValue()}")

回答4:

Keep in mind, that the initialDelayString is evaluated only once at startup and than this same values is used whenever the job is scheduled.

See org.springframework.scheduling.annotation.ScheduledAnnotationBeanPostProcessor#processScheduled

回答5:

In kotlin this works:

@Component
class MyJob {
   companion object {
      const val INTERVAL = 24*3600*1000L // once a day
   }

   @Scheduled(fixedRate = INTERVAL, initialDelayString = "\${random.long($INTERVAL)}")
   fun doDaily() {
      ...
   }
}

回答6:

Or you could just add Thread.sleep(...) at the end of your function.

@Scheduled(fixedDelay = 10000)
public void replicateData() {

    ... do stuff ...

    try {
        Thread.sleep(RandomUtils.nextLong(1000, 10000));
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
}