Spring boot @Async annotation with @Scheduled

Question

Please explain how does @Async annotation works with @Scheduled tasks. For example, i have class:

@Configuration
@EnableScheduling
@ConditionalOnProperty(name = "scheduler.enabled", matchIfMissing = true)
@RequiredArgsConstructor
@EnableAsync
public class Scheduler {
    private final ReportService reportService;

    @Scheduled(cron = "${scheduler.create-reports.cron}")
    @Async
    public void createDailyReports() {
        // TODO: Make request to team-service to find all students id's. Then create new empty reports
        List<Long> studentIdList = new ArrayList<>();
        reportService.createEmptyDailyReports(studentIdList);
    }
}

Is it necessary to annotate inner reportService.createEmptyDailyReports method with @Async to process whole createDailyReports() in async or @Async on createDailyReports() is enough?

In my mind one @Async is enough. Thanks for explanation

Answer 1

Basically the @Aysnc annotation uses the SimpleAsyncTaskExecutor which is implemented to fire up a new Thread for each task, executing it asynchronously.

Implementation details:

Async annotation uses SimpleAsyncTaskExecutor by default. As mentioned in the docs, this executor does not reuse threads!, rather it starts up a new thread for each invocation. However, it supports a concurrency limit. By default, the number of concurrent threads is unlimited. That means each invocation of a method that is annotated with Async annotation will be running with a new thread.

Now, with the @Async annotation the scheduled method will executed asynchronously with a new thread every time, here is the example with more information

Don’t forget to add @EnableAsync and @EnableScheduling annotations in a Configuration class or Main class