Spring Boot如何识别子类方法上的@Scheduled？

Question

Let's take an example of a simple Spring Boot program:

Application.java

@SpringBootApplication
@EnableScheduling
public class Application {

    public static void main(String[] args) throws Exception {
        SpringApplication.run(Application.class);
    }
}

SuperClass.java

public abstract class SuperClass {

    @Scheduled(fixedRate = 5000)
    public void printSomething() {
        System.out.println("this is the super method");
    }
}

SubClass.java

@Component
public class SubClass extends SuperClass {

}

According to this answer, only annotations annotated by @Inherited are inherited by subclasses, and @Scheduled does not have such an annotation. So how come this is working?

Answer 1

@Inherited only applies to class types, not methods.

Note that this meta-annotation type has no effect if the annotated type is used to annotate anything other than a class. Note also that this meta-annotation only causes annotations to be inherited from superclasses; annotations on implemented interfaces have no effect.

When Spring scans beans for the @Scheduled annotation (or others), it looks for all methods in the bean class. SubClass has a printSomething so Spring decides it can enhance it with the scheduling behavior.

---

Spring handles @Scheduled a little differently than the standard proxying mechanism and is able to invoke private methods annotated with it.

Had you overriden the printSomething method in the subclass and omitted the @Scheduled annotation on that declaration, Spring would not have applied the scheduling behavior.