The service layer in JAVA three-tier architecture

In Java, business logic (Business Logic) is usually placed in the Service layer instead of directly in the Controller or DAO layer. The Service layer is a component used to encapsulate and process business logic. It is separated from the data access layer (DAO layer) and the presentation layer (Controller layer). It follows the principle of layered design and improves the maintainability and scalability of the code. sex.

In order to realize the functions of the Service layer, the Service is usually defined as an interface (Service Interface), and then an implementation class (Service Implementation) of the interface is created. This design pattern is called the "Service Interface and Implementation" pattern.

The benefits of using Service interfaces and implementation classes include:

1. Loose coupling: Service interface separates business logic from specific implementation. Controller and other components can interact through the interface without caring about specific implementation.

2. Replaceability: Due to the use of interfaces, the implementation class of Service can be easily replaced without affecting other code. This is particularly useful when unit testing, where mock implementations can be used to test other components such as Controllers.

3. Extensibility: Business logic can be extended by adding new Service implementation classes without modifying other code. This makes it easier for applications to adapt to new needs and functionality.

4. Code specifications: Placing business logic in the Service layer helps to follow the single responsibility principle and code specifications, making the code easier to understand and maintain.

Example:

// Service接口
public interface UserService {
    // 业务逻辑方法
    User getUserById(int userId);
    void saveUser(User user);
}

// Service实现类
@Service
public class UserServiceImpl implements UserService {

    private final UserRepository userRepository; // 使用依赖注入注入DAO层

    @Autowired
    public UserServiceImpl(UserRepository userRepository) {
        this.userRepository = userRepository;
    }

    // 业务逻辑方法的具体实现
    @Override
    public User getUserById(int userId) {
        return userRepository.findById(userId);
    }

    @Override
    public void saveUser(User user) {
        userRepository.save(user);
    }

   
}