Can you explain the differences between components, services, repositories, controllers, and REST controllers in the Spring framework?

In Spring, there are different types of components, each serving its own role:

• @Component — the basic annotation for any Spring bean. Used to denote a class as a component managed by the Spring container.

• @Service — a specialized component that typically contains business logic. It is a semantic clarification to emphasize that the class implements a service layer.

• @Repository — a component responsible for data access (DAO). Besides being a component, Spring handles database-related exceptions and translates them into its unchecked exceptions.

• @Controller — a component that handles HTTP requests and returns views (e.g., JSP, Thymeleaf). Usually used in MVC applications.

• @RestController — a combination of @Controller and @ResponseBody. Used to create REST APIs, automatically serializing returned objects into JSON or XML.

Example:

@Service
public class UserService {
    // business logic
}

@Repository
public class UserRepository {
    // database access
}

@RestController
public class UserController {
    private final UserService userService;

    public UserController(UserService userService) {
        this.userService = userService;
    }

    @GetMapping("/users")
    public List<User> getAllUsers() {
        return userService.findAllUsers();
    }
}