Spring Stereotype Annotation Hierarchy

Direct Answer

All Spring stereotype annotations are meta-annotated with @Component. This means @Service, @Repository, and @Controller have @Component inside their annotation definitions, forming an annotation hierarchy. Component scanning finds them all by looking for @Component, while each stereotype preserves its semantic meaning. @RestController is meta-annotated with @Controller, extending the hierarchy further.

Code Example

// Spring's actual definition of @Service (simplified)
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component  // Meta-annotation: @Service includes @Component
public @interface Service {
    @AliasFor(annotation = Component.class)
    String value() default "";
}

// Spring's actual definition of @RestController (simplified)
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Controller  // Meta-annotated with @Controller (which has @Component)
@ResponseBody  // Adds behavior: auto-serialize return values to JSON
public @interface RestController {
    @AliasFor(annotation = Controller.class)
    String value() default "";
}

// Your code using the composed annotations
@Service  // Implicitly includes @Component
public class OrderService {
    // Spring finds this during component scan because @Service has @Component
}

@RestController  // Has @Controller, which has @Component
public class OrderController {
    // Spring finds this AND applies @ResponseBody behavior automatically
}

Common Mistakes & Pitfalls

• Thinking stereotypes are independent: Learners often believe @Service and @Repository are completely separate annotations with no relationship. They don't realize component scanning works by looking for @Component, which all stereotypes inherit. This misunderstanding causes confusion when learning about custom component scanning filters.
• Not recognizing annotation composition: When using @RestController, Learners don't realize it combines @Controller and @ResponseBody. They might redundantly add @ResponseBody to methods, not knowing it's already inherited from the class-level annotation.
• Missing the extensibility point: Learners don't see that they can create their own stereotype annotations by meta-annotating with @Component. This leads to overusing @Component directly instead of creating semantically meaningful custom stereotypes like @Adapter or @Gateway that document domain concepts while still being detected as beans.