Commonly Used Spring Annotations

1. @Component

• Marks a class as a Spring bean, allowing Spring to manage it.
• Can be used for general-purpose components.

@Component
public class MyComponent {
    // class body
}

2. @Service

• A specialization of @Component, used for service layer classes.
• Typically used for classes containing business logic.

@Service
public class MyService {
    // service logic
}

3. @Repository

• A specialization of @Component, typically used for data access layers.
• Marks a class as a repository (DAO), often interacting with a database.

@Repository
public class MyRepository {
    // data access logic
}

4. @Controller

• A specialization of @Component, used to define web controllers in Spring MVC.
• Typically used for handling HTTP requests in a Spring web application.

@Controller
public class MyController {
    // handler methods
}

5. @RestController

• A specialized version of @Controller, includes @ResponseBody by default.
• Used for creating RESTful web services in Spring.

@RestController
public class MyRestController {
    // REST API methods
}

6. @Qualifier

• Used with @Autowired to specify which bean to inject when multiple candidates exist.

@Autowired
@Qualifier("myService")
private MyService myService;

7. @Configuration

• Marks a class as a source of bean definitions.
• Used to define configuration classes in Java-based configuration.

@Configuration
public class AppConfig {
    @Bean
    public MyService myService() {
        return new MyService();
    }
}

8. @Bean

• Defines a Spring bean inside a @Configuration class.

@Configuration
public class AppConfig {
    @Bean
    public MyService myService() {
        return new MyService();
    }
}

9. @PathVariable

• Extracts values from the URI path.

@GetMapping("/hello/{name}")
public String hello(@PathVariable String name) {
    return "Hello, " + name;
}

10. @RequestParam

• Extracts query parameters from the request URL.

@GetMapping("/hello")
public String hello(@RequestParam String name) {
    return "Hello, " + name;
}

11. @RequestBody

• Binds the HTTP request body to a method parameter in a controller.
• Used to handle JSON or XML data from the request body.

@PostMapping("/user")
public String createUser(@RequestBody User user) {
    return "User created: " + user.getName();
}

12. @ExceptionHandler

• Handles exceptions in Spring MVC controllers.

@ExceptionHandler(Exception.class)
public String handleException(Exception e) {
    return "error";
}