Layered Architecture

In a Spring application, the layered architecture is a common design pattern that separates the application into distinct layers, each with specific responsibilities. This architecture promotes separation of concerns, modularity, and maintainability. Here are the primary layers in a typical Spring application:

1. Presentation Layer (Web Layer)

• Purpose: Handles user interaction and input, and renders the user interface.
• Components: Controllers, REST controllers, views, and templates.
• Technologies: Spring MVC (Model-View-Controller), Thymeleaf, JSP (JavaServer Pages).
• Example:

  @Controller
  public class UserController {
      @GetMapping("/users")
      public String getAllUsers(Model model) {
          List<User> users = userService.findAllUsers();
          model.addAttribute("users", users);
          return "users";
      }
  }
  

2. Service Layer (Business Logic Layer)

• Purpose: Contains the business logic and service components that perform operations.
• Components: Service classes and business logic.
• Technologies: Spring Services, Spring Transactions.
• Example:

  @Service
  public class UserService {
      @Autowired
      private UserRepository userRepository;
  
      public List<User> findAllUsers() {
          return userRepository.findAll();
      }
  }
  

3. Data Access Layer (Persistence Layer)

• Purpose: Manages data access, storage, and retrieval operations.
• Components: Repositories, DAO (Data Access Objects), and ORM (Object-Relational Mapping) frameworks.
• Technologies: Spring Data JPA, Hibernate, JDBC (Java Database Connectivity).
• Example:

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

4. Domain Layer (Model Layer)

• Purpose: Represents the core business objects and domain logic.
• Components: Entity classes, domain models, and value objects.
• Technologies: JPA (Java Persistence API) annotations, JavaBeans.
• Example:

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

5. Configuration Layer

• Purpose: Centralizes application configuration and settings.
• Components: Configuration classes, properties files.
• Technologies: Spring Boot application.properties/yaml, @Configuration, @Bean annotations.
• Example:

  @Configuration
  public class AppConfig {
      @Bean
      public DataSource dataSource() {
          return new HikariDataSource();
      }
  }
  

Interaction Between Layers

• Controller (Presentation Layer) interacts with the Service Layer to process user input and handle requests.
• Service Layer contains the business logic and interacts with the Data Access Layer to retrieve or save data.
• Data Access Layer (Persistence Layer) uses repositories or DAOs to perform database operations.
• Domain Layer (Model Layer) represents the data structures used across different layers.
• Configuration Layer holds the necessary configurations for the application.

Benefits of Layered Architecture

• Separation of Concerns: Each layer has a specific responsibility, making the application easier to manage and maintain.
• Modularity: Enhances code reusability and enables independent development and testing of each layer.
• Scalability: Allows the application to scale more effectively by isolating business logic from data access logic.
• Maintainability: Simplifies debugging, testing, and updating the application.

The layered architecture is a fundamental design pattern in Spring applications that provides a clear structure, making the application more robust, scalable, and maintainable.