Spring ScheduledTask - start/stop support?

Question

Is there a way to start or stop a task scheduled using Spring Scheduled Tasks initialized using context file or @Scheduled annotation?

I would like to start the task when required and stop it when the task is no longer needed to be run.

If this is not possible, any alternative to injecting spring variables to a thread?

Answer 1

Here is an example of starting/stopping a scheduled method in Spring Boot. You can use such APIs:
http:localhost:8080/start - for starting scheduled method with fixed rate 5000 ms
http:localhost:8080/stop - for stopping scheduled method

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.scheduling.TaskScheduler;
import org.springframework.scheduling.concurrent.ThreadPoolTaskScheduler;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import java.time.Instant;
import java.util.concurrent.ScheduledFuture;

@Configuration
@ComponentScan
@EnableAutoConfiguration    
public class TaskSchedulingApplication {

    public static void main(String[] args) {
        SpringApplication.run(TaskSchedulingApplication.class, args);
    }

    @Bean
    TaskScheduler threadPoolTaskScheduler() {
        return new ThreadPoolTaskScheduler();
    }
}

@Controller
class ScheduleController {

    public static final long FIXED_RATE = 5000;

    @Autowired
    TaskScheduler taskScheduler;

    ScheduledFuture<?> scheduledFuture;

    @RequestMapping("start")
    ResponseEntity<Void> start() {
        scheduledFuture = taskScheduler.scheduleAtFixedRate(printHour(), FIXED_RATE);

        return new ResponseEntity<Void>(HttpStatus.OK);
    }

    @RequestMapping("stop")
    ResponseEntity<Void> stop() {
        scheduledFuture.cancel(false);
        return new ResponseEntity<Void>(HttpStatus.OK);
    }

    private Runnable printHour() {
        return () -> System.out.println("Hello " + Instant.now().toEpochMilli());
    }

}

Answer 2

Stopping registered @Scheduled beans is not standard feature since the access to them is private in the org.springframework.scheduling.annotation.ScheduledAnnotationBeanPostProcessor.

If you need to manage the time they run you need to register them programmatically (TriggerTask): see the documentation to org.springframework.scheduling.annotation.SchedulingConfigurer. In the type org.springframework.scheduling.config.TriggerTask there is the method which returns type of org.springframework.scheduling.Trigger. There you can manage next execution time.

TriggerTasks could be beans in the case of programmatical registration.

Answer 3

Have the @Scheduled method look for a variable held in Application state or ServletContext, or from a value stored in the DB. If the value is TRUE, proceed with the task; if FALSE, don't start. This setup will control the scheduled run.

If you want to also be able to fire the task at will, reference the task's method from a Controller; that way you can fire it at will. Additionally, if its a longer running task, create a second method annotated @Async and call that method from your Controller so that it runs in its own thread.