Stereotype Annotations in Spring Framework

The Spring Framework provides several powerful annotations that help in building clean, modular, and maintainable applications. Among them, the Stereotype Annotations play a crucial role in defining Spring-managed components. In this blog, we will explore what stereotype annotations are, their types, and when to use them with real-world examples and a visual diagram.

📌 What are Stereotype Annotations?

Stereotype annotations in Spring are special annotations that indicate a class should be registered as a Spring bean. These annotations are part of the org.springframework.stereotype package. They also help categorize Spring beans based on their roles (e.g., controller, service, repository).

🔹 Common Stereotype Annotations

Spring provides the following stereotype annotations:

• @Component
• @Service
• @Repository
• @Controller

1. @Component

This is the most generic annotation that indicates the class is a Spring component (bean).

import org.springframework.stereotype.Component;

@Component
public class MyUtility {
    public void print() {
        System.out.println("This is a utility class.");
    }
}

2. @Service

Used to annotate service-layer classes. It's a specialization of @Component.

import org.springframework.stereotype.Service;

@Service
public class UserService {
    public String getUser() {
        return "John Doe";
    }
}

3. @Repository

Used for DAO (Data Access Object) classes. It also enables exception translation into Spring's data access exceptions.

import org.springframework.stereotype.Repository;

@Repository
public class UserRepository {
    public void saveUser(String name) {
        // Simulate saving user
    }
}

4. @Controller

Used in web applications to define controller classes that handle HTTP requests.

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.ResponseBody;

@Controller
public class HomeController {

    @GetMapping("/")
    @ResponseBody
    public String home() {
        return "Welcome to Spring!";
    }
}

🧠 Internal Structure of Stereotype Annotations

All these annotations internally use @Component. That means they are just specialized forms of @Component with additional semantics.

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component
public @interface Service {
    String value() default "";
}

🖼️ Diagram: Spring Stereotype Annotation Hierarchy

Diagram: All stereotype annotations in Spring derive from @Component

⚙️ How Spring Registers These Beans

To enable Spring to scan and register classes with stereotype annotations, you need to use @ComponentScan:

@Configuration
@ComponentScan(basePackages = "com.example")
public class AppConfig {
}

✅ When to Use What?

• @Component: For generic Spring-managed beans.
• @Service: For business logic and service classes.
• @Repository: For database interaction and DAO layers.
• @Controller: For web controllers that handle HTTP requests.

🧩 Conclusion

Stereotype annotations not only help Spring register your classes as beans but also bring clarity and structure to your code. They make your application more readable and maintainable. Always use the most specific annotation that fits your class's role to follow Spring’s design philosophy and best practices.

📎 References

• Spring Official Documentation
• Spring Guides

Happy Spring-ing! 🌱