Mastering Spring Boot Scheduled Tasks: From Basics to Distributed Locks

We often need to send SMS, emails, or monitor flags periodically in Spring Boot applications.

Create Scheduled Task

In Spring Boot, creating a scheduled task is simple. Add @EnableScheduling to the main class to enable scheduling.

@SpringBootApplication
@EnableScheduling
public class Application {
    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }
}

Create a component that contains the scheduled method.

@Component
public class ScheduledTasks {
    private static final SimpleDateFormat dateFormat = new SimpleDateFormat("HH:mm:ss");

    @Scheduled(fixedRate = 5000)
    public void reportCurrentTime() {
        log.info("现在时间：" + dateFormat.format(new Date()));
    }
}

Running the application prints the current time every five seconds.

2021-07-13 14:57:01.411  INFO ... : 现在时间：14:57:01
2021-07-13 14:57:06.412  INFO ... : 现在时间：14:57:06
...

@Scheduled Annotation Details

The @Scheduled annotation can be configured with several attributes extracted from its source:

@Target({ElementType.METHOD, ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Repeatable(Schedules.class)
public @interface Scheduled {
    String cron() default "";
    String zone() default "";
    long fixedDelay() default -1;
    String fixedDelayString() default "";
    long fixedRate() default -1;
    String fixedRateString() default "";
    long initialDelay() default -1;
    String initialDelayString() default "";
}

cron: use a cron expression to define execution rules.

zone: time zone for cron parsing.

fixedDelay: interval between the end of the last execution and the start of the next (ms).

fixedDelayString: same as fixedDelay but parsed with java.time.Duration.

fixedRate: interval between the start of successive executions (ms); if a previous execution is still running, it is queued.

fixedRateString: same as fixedRate with Duration parsing.

initialDelay: delay before the first execution.

initialDelayString: same as initialDelay with Duration parsing.

Considerations and Advanced Topics

While this approach works in a single‑process environment, it lacks coordination in a clustered deployment. Multiple instances would trigger the task simultaneously, leading to duplicate processing or data inconsistency.

To avoid this, use a distributed lock (e.g., Redis, Zookeeper) so that only one instance runs the task at a time.

Full Project Example

The complete source code is available in the chapter7-1 directory of the repository:

GitHub: https://github.com/dyc87112/SpringBoot-Learning/tree/master/2.x

Gitee: https://gitee.com/didispace/SpringBoot-Learning/tree/master/2.x