How does Spring handle scheduling and task execution?

Question

Accepted Answer

Spring handles scheduled and periodic task execution through the @Scheduled annotation, which lets a method run on a fixed interval, a delay, or a cron expression.

Key Points:
• @EnableScheduling on a configuration class turns on Spring's task scheduler.
• fixedRate runs the method at a constant interval regardless of how long the previous run took; fixedDelay waits for the previous run to finish first.
• The cron attribute supports full cron expressions for calendar-based schedules (e.g. nightly at 2am).
• By default, all @Scheduled methods share a single thread, so a slow task can delay others unless a custom TaskScheduler with a thread pool is configured.
• @Async, combined with @EnableAsync, lets long-running tasks run on separate threads instead of blocking the caller.

Example:
A nightly cleanup job that deletes expired records can be scheduled with @Scheduled(cron = "0 0 2 * * *") to run every day at 2am without any external cron setup.

Code Example:
```
@Configuration
@EnableScheduling
public class SchedulingConfig {
}

@Component
public class CleanupJob {

@Scheduled(cron = "0 0 2 * * *")
    public void purgeExpiredRecords() {
        // cleanup logic
    }
}
```

Interview Tip:
A concise interview answer is:

"I use @Scheduled methods, enabled with @EnableScheduling, to run tasks on a fixed rate, fixed delay, or cron expression without an external scheduler. Since all scheduled tasks share one thread by default, I configure a custom TaskScheduler with a thread pool, or use @Async, when tasks need to run in parallel."