Understanding Spring Boot Application Structure: Controllers, DAOs, Entities, Services, and More

Understanding Spring Boot Application Structure: Controllers, DAOs, Entities, Services, and More

When developing a Spring Boot application, organizing your codebase into well-defined layers and packages is crucial. This not only helps maintain a clean architecture but also makes the codebase easier to understand and maintain. In this blog post, we'll explore the roles of various components in a typical Spring Boot application: Controller, DAO, Entity, Service, RequestModel, ResponseModel, and Utils. We'll also discuss how they fit into the typical folder structure.

Key Components of a Spring Boot Application

1. Controller

Role:
Controllers handle HTTP requests and responses, acting as the entry point for client interactions. They map incoming requests to appropriate service methods.

@RestController
@RequestMapping("/users")
public class UserController {
    @Autowired
    private UserService userService;

    @GetMapping("/{id}")
    public ResponseEntity<UserResponseModel> getUser(@PathVariable Long id) {
        return ResponseEntity.ok(userService.getUserById(id));
    }
}

Folder Structure:
/src/main/java/com/example/app/controller

2. DAO (Data Access Object)

Role:
DAOs manage data access logic and communicate with the database, encapsulating the details of data persistence and retrieval.

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

Folder Structure:
/src/main/java/com/example/app/dao

3. Entity

Role:
Entities represent the data model or domain object, mapping to the database table using JPA (Java Persistence API).

@Entity
@Table(name = "users")
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private String email;
    // Getters and Setters
}

Folder Structure:
/src/main/java/com/example/app/entity

4. Service

Role:
Services contain business logic and interact with DAOs to perform operations.

@Service
public class UserService {
    @Autowired
    private UserDao userDao;

    public UserResponseModel getUserById(Long id) {
        User user = userDao.findById(id).orElseThrow(() -> new ResourceNotFoundException("User not found"));
        return new UserResponseModel(user);
    }
}

Folder Structure:
/src/main/java/com/example/app/service

5. RequestModel

Role:
RequestModels define the structure of data expected in HTTP request bodies, used for data validation and mapping client input to service layer.

public class UserRequestModel {
    @NotNull
    private String name;
    @NotNull
    @Email
    private String email;
    // Getters and Setters
}

Folder Structure:
/src/main/java/com/example/app/model/request

6. ResponseModel

Role:
ResponseModels define the structure of data sent back in HTTP responses, used for standardizing API responses and ensuring consistent data output.

public class UserResponseModel {
    private Long id;
    private String name;
    private String email;

    public UserResponseModel(User user) {
        this.id = user.getId();
        this.name = user.getName();
        this.email = user.getEmail();
    }
    // Getters and Setters
}

Folder Structure:
/src/main/java/com/example/app/model/response

7. Utils

Role:
Utility classes and methods provide common functionality and helper methods that can be reused across the application.

public class DateUtils {
    public static String formatDate(LocalDate date) {
        return date.format(DateTimeFormatter.ofPattern("yyyy-MM-dd"));
    }
}

Folder Structure:
/src/main/java/com/example/app/utils

Overall Folder Structure

Here's a summary of how these components fit into the overall project structure:

/src/main/java/com/example/app
    /controller
        UserController.java
    /dao
        UserDao.java
    /entity
        User.java
    /service
        UserService.java
    /model
        /request
            UserRequestModel.java
        /response
            UserResponseModel.java
    /utils
        DateUtils.java

Example Application Walkthrough

UserController.java

@RestController
@RequestMapping("/users")
public class UserController {
    @Autowired
    private UserService userService;

    @GetMapping("/{id}")
    public ResponseEntity<UserResponseModel> getUser(@PathVariable Long id) {
        return ResponseEntity.ok(userService.getUserById(id));
    }
}

UserService.java

@Service
public class UserService {
    @Autowired
    private UserDao userDao;

    public UserResponseModel getUserById(Long id) {
        User user = userDao.findById(id).orElseThrow(() -> new ResourceNotFoundException("User not found"));
        return new UserResponseModel(user);
    }
}

UserDao.java

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

User.java

@Entity
@Table(name = "users")
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private String email;
    // Getters and Setters
}

UserRequestModel.java

public class UserRequestModel {
    @NotNull
    private String name;
    @NotNull
    @Email
    private String email;
    // Getters and Setters
}

UserResponseModel.java

public class UserResponseModel {
    private Long id;
    private String name;
    private String email;

    public UserResponseModel(User user) {
        this.id = user.getId();
        this.name = user.getName();
        this.email = user.getEmail();
    }
    // Getters and Setters
}

DateUtils.java

public class DateUtils {
    public static String formatDate(LocalDate date) {
        return date.format(DateTimeFormatter.ofPattern("yyyy-MM-dd"));
    }
}

By organizing your Spring Boot application into clearly defined layers and packages, you can ensure a clean and maintainable codebase. Each component has a specific role, making the application modular and scalable.