Hackforge Academy

Category: React • Beginner

Published on 02 Apr 2026

Explanation

The main class is the entry point of the Spring Boot application. It contains the @SpringBootApplication annotation and starts the embedded server using SpringApplication.run().

Code Example

src/main/java/com/example/demo/
DemoApplication.java

@SpringBootApplication
public class DemoApplication {
  public static void main(String[] args) {
    SpringApplication.run(DemoApplication.
class, args);
  }
}

Explanation

The controller layer handles HTTP requests from clients and returns responses. It uses annotations like @RestController and @RequestMapping.

Code Example

src/main/java/com/example/demo/controller/
UserController.java

@RestController
@RequestMapping("/users")
public class UserController {

  @GetMapping
  public String getUsers() {
    return "List of users";
  }
}

Explanation

The service layer contains business logic. It acts as a bridge between controller and repository layers.

Code Example

src/main/java/com/example/demo/service/
UserService.java

@Service
public class UserService {

  public String getUserServiceMessage() {
    return "Business logic executed";
  }
}

Explanation

The repository layer interacts with the database. It usually extends JpaRepository to perform CRUD operations.

Code Example

src/main/java/com/example/demo/repository/
UserRepository.java

@Repository
public interface UserRepository extends
 JpaRepository<User, Long> {
}

Explanation

The resources folder contains configuration files like #white-application.properties #white-static files #white-template files required for the application.

Code Example

src/main/resources/
 ├── application.properties
 ├── static/
 └── templates/