How to force Micronaut scheduled jobs wait for application startup to complete?

Question

I implemented some scheduled jobs in my micronaut application with the @Scheduled - annotation like described here: https://guides.micronaut.io/latest/micronaut-scheduled-gradle-java.html
This works just fine except that all jobs get executed before the application startup is completed. That is a problem because my startup process contains executing of db update jobs and stuff that needs to be done before everything else.
So how do I force all scheduled jobs to wait until the application start process is finished?
With "finished" I mean the moment

[main] INFO io.micronaut.runtime.Micronaut - Startup completed in 9127ms. Server Running: http://localhost:8080

appears in my console.

I know I could schedule all my jobs manually, but that would mean to implement an event listener to all my classes that contains scheduled tasks. I don't want to rely on other devs to remember this and it sounds like too much work for such a simple requirement.

Answer 1

The simplest way to achieve it is to use Micronaut 4 expression language and an event listener.

Given the following job we are using the expression language value #{!this.paused} to pause the job unless the boolean flag paused is set to false.

@Singleton
public class SomeJob {

    private boolean paused = true;

    @Scheduled(fixedRate = "5m", condition = "#{!this.paused}" )
    public void doSomething() {
        System.out.println("The job runs...");
    }

    public boolean isPaused() {
        return paused;
    }

    @EventListener
    public void onStartup(StartupEvent event) {
        this.paused = false;
    }
}

Note that the expression language is a Micronaut 4 feature and not available in previous versions of Micronaut.

If you have multiple jobs you could implement something like this.

public sealed interface Pausable {
    void pause();
    void unpause();

    @Singleton
    final class SomeJobA implements Pausable {

        private boolean paused = true;

        @Scheduled(fixedRate = "5m", condition = "#{!this.paused}" )
        public void doSomething() {
            System.out.println("The job runs...");
        }

        @Override
        public void pause() { this.paused = true; }

        @Override
        public void unpause() { this.paused = false; }
    }

    @Singleton
    final class SomeJobB implements Pausable {

        private boolean paused = true;

        @Scheduled(fixedRate = "5m", condition = "#{!this.paused}" )
        public void doSomething() {
            System.out.println("The job runs...");
        }

        @Override
        public void pause() { this.paused = true; }

        @Override
        public void unpause() { this.paused = false; }
    }
}

Then you implement the event listener in your Application.java.

@Singleton
public class Application {

  private static ApplicationContext ctx;

  public static void main(String[] args) {
    ctx = Micronaut.run(Application.class, args);
  }

  @EventListener
  public void onStartup(StartupEvent event) {
    ctx.getBeansOfType(Pausable.class).forEach(Pausable::unpause);
  }
}