Spring Boot @Component, @Controller, @Repository and @Service

In this tutorial, we will learn about Spring Stereotype Annotations such as @Component, @Controller,  @Repository, and @Service annotations.

Spring Stereotype Annotations

Spring Stereotype annotations are used to create Spring beans automatically in the application context (Spring IoC container).

The main stereotype annotation is @Component. By using this annotation, Spring provides more Stereotype meta-annotations such as @Service, @Repository, and @Controller.

@Service annotation is used to create Spring beans at the Service layer.

@Repository is used to create Spring beans for the repositories at the DAO layer.

@Controller is used to create Spring beans at the controller layer.

YouTube Video - @Controller, @Repository and @Service

@Component

The @Component annotation indicates that an annotated class is a “spring bean/component”. Such classes are considered candidates for auto-detection when using annotation-based configuration and classpath scanning.

Here's an example of a simple Java class that is annotated as a Spring component:

import org.springframework.stereotype.Component;

@Component
public class HelloWorldComponent {
    public void printHello() {
        System.out.println("Hello, Spring!");
    }
}

In this example, the @Component annotation tells Spring that this class should be treated as a bean. 

Next, you can use this bean in other parts of your application by injecting it using the @Autowired annotation, as in:

import org.springframework.beans.factory.annotation.Autowired;

@Component
public class AnotherBean {
    @Autowired
    private HelloWorldComponent helloWorldComponent;

    public void printHello() {
        helloWorldComponent.printHello();
    }
}

Next, you need to specify the package to scan for classes annotated with @Component using the @ComponentScan annotation in a Spring configuration class. This will automatically register any classes annotated with @Component as beans in the application context.

import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;

@Configuration
@ComponentScan("com.javaguides.beans")
public class AppConfig {
}

The above configuration will scan the package "com.example.javaguides.beans" for classes annotated with @Component, @Service, @Repository, and @Controller and register them as beans in the Spring application context.

@Service 

The @Service annotation is also a specialization of @Component annotation. Basically, @Service annotation is used to create Spring beans at the Service layer.

import org.springframework.stereotype.Service;

@Service
public class UserServiceImpl implements UserService {
      // All the service layer logic goes here
}

Check out the complete example at Spring @Service Annotation

@Repository 

The @Repository annotation is also a specialization of @Component annotation. Basically, @Repository is used to create Spring beans for the repositories at the DAO layer.

import org.springframework.stereotype.Repository;

@Repository
public class UserDaoImpl implements UserDao {
      // All the dao layer logic goes here
}

Check out the complete example at Spring @Repository Annotation

@Controller

The @Controller annotation is also a specialization of @Component annotation. Basically, @Controller is used to create Spring beans at the controller layer.

import org.springframework.stereotype.Controller;

@Controller
public class UserController {
      // Build REST APIs
}

Check out the complete example at The Spring @Controller and @RestController Annotations with Examples

Conclusion

In this tutorial, we learned about Spring Stereotype Annotations such as @Component, @Controller, @Repository, and @Service annotations.

Related Spring and Spring Boot Annotations

• Spring Boot @Bean Annotation Example
• Spring @Qualifier Annotation Example
• Spring @Autowired Annotation with Example
• Spring @Bean Annotation with Example
• Spring @Configuration Annotation with Example
• Spring @PropertySource Annotation with Example
• Spring @Import Annotation with Example
• Spring @ImportResource Annotation Example
• Spring - @Lazy Annotation Example
• Spring - @Primary Annotation Example
• Spring @PostConstruct and @PreDestroy Example
• Spring @Repository Annotation
• Spring @Service Annotation 
• The Spring @Controller and @RestController Annotations
• Spring Boot @Component, @Controller, @Repository and @Service
• Spring @Scope annotation with Prototype Scope Example
• Spring @Scope annotation with Singleton Scope Example
• Spring Boot @PathVariable
• Spring Boot @ResponseBody
• Spring @RequestBody - Binding Method Parameters to Request Body
• Spring Boot @ResponseStatus Annotation
• Spring Boot - Creating Asynchronous Methods using @Async Annotation
• @SpringBootTest Spring Boot Example
• @SpringBootTest vs @WebMvcTest
• @DataJpaTest Spring Boot Example
• Spring @PostConstruct and @PreDestroy Example
• Spring @GetMapping, @PostMapping, @PutMapping, @DeleteMapping and @PatchMapping
• Spring Boot @EnableAutoConfiguration Annotation with Example
• Spring Boot @SpringBootApplication Annotation with Example

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