What are Spring Scheduling Annotations in Java? Tutorial [2022]

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Spring Scheduling Annotations

Spring provides annotation support for both task scheduling and asynchronous method execution so we’re going to explore the Spring Scheduling Annotations.

Spring Scheduling Annotations

@Schedule
@EnabaleScheduling
@Async
@EnableAsync
@Schedules

@Scheduled Annotation

The @Scheduled annotation is added to a method along with some information about when to execute it, and Spring takes care of the rest.

For example, the following method would be invoked every 5 seconds with a fixed delay, meaning that the period will be measured from the completion time of each preceding invocation.
```
@Scheduled(fixedDelay=5000)
publicvoiddoSomething() {
// something that should execute periodically
}
```
If a fixed rate execution is desired, simply change the property name specified within the annotation. The following would be executed every 5 seconds measured between the successive start times of each invocation.
```
@Scheduled(fixedRate=5000)
publicvoiddoSomething() {
// something that should execute periodically
}
```
For fixed-delay and fixed-rate tasks, an initial delay may be specified indicating the number of milliseconds to wait before the first execution of the method.
```
@Scheduled(initialDelay=1000, fixedRate=5000)
publicvoiddoSomething() {
// something that should execute periodically
}
```
If simple periodic scheduling is not expressive enough, then a cron expression may be provided. For example, the following will only execute on weekdays.
```
@Scheduled(cron="*/5 * * * * MON-FRI")
publicvoiddoSomething() {
// something that should execute on weekdays only
}
```
@EnableScheduling Annotation

@EnableScheduling annotation is used to enable scheduling in the application. We also have to use it in conjunction with @Configuration:
```
@Configuration
@EnableScheduling
publicclassAppconfig{}
```
As a result, we can now run methods periodically with @Scheduled.
@Async Annotation

The @Async annotation can be provided on a method so that invocation of that method will occur asynchronously. In other words, the caller will return immediately upon invocation and the actual execution of the method will occur in a task that has been submitted to a Spring TaskExecutor. In the simplest case, the annotation may be applied to a void-returning method.
```
@Async
voiddoSomething() {
// this will be executed asynchronously
}
```
Unlike the methods annotated with the @Scheduled annotation, these methods can expect arguments, because they will be invoked in the “normal” way by callers at runtime rather than from a scheduled task being managed by the container.

For example, the following is a legitimate application of the @Async annotation.
```
@Async
voiddoSomething(String s) {
// this will be executed asynchronously
}
```
Even methods that return a value can be invoked asynchronously. However, such methods are required to have a Future typed return value. This still provides the benefit of asynchronous execution so that the caller can perform other tasks prior to calling get() on that Future.
```
@Async
Future< String>returnSomething(inti) {
// this will be executed asynchronously
}
```
@Async cannot be used in conjunction with lifecycle callbacks such as @PostConstruct. To asynchronously initialize Spring beans you currently have to use a separate initializing Spring bean that invokes the @Async annotated method on the target then.
```
publicclassSampleBeanImplimplementsSampleBean {
@Async
voiddoSomething() {
// ...
    }
}

publicclassSampleBeanInitializer {

privatefinalSampleBean bean;

publicSampleBeanInitializer(SampleBeanbean) {
this.bean= bean;
    }

@PostConstruct
publicvoidinitialize() {
bean.doSomething();
    }
}
```
@EnableAsync Annotation

With this annotation, we can enable asynchronous functionality in Spring. We must use it with @Configuration:
```
@Configuration
@EnableAsync
publicclassAppConfig{}
```
Now, that we enabled asynchronous calls, we can use @Async to define the methods supporting it.

@Schedules Annotation

We can use this annotation to specify multiple @Scheduled rules:

@Schedules({
@Scheduled(fixedRate=10000), 
@Scheduled(cron="0 * * * * MON-FRI")
})
voidcheckVehicle() {
// ...
}

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Spring Scheduling Annotations

Quick Contact

Java Tutorial

Springboot

Hibernate

JAVA FX

Spring Scheduling Annotations

Spring Scheduling Annotations

@Scheduled Annotation

@EnableScheduling Annotation

@Async Annotation

@EnableAsync Annotation

@Schedules Annotation