Dependency Injection (DI) is a design pattern that allows objects to receive their dependencies from an external source rather than creating them internally. It promotes loose coupling and enhances testability and maintainability by separating object creation from usage.

  • How it works:
    • In DI, dependencies are injected into an object via constructors, setters, or field injection.
    • The Spring Framework manages this process, automatically injecting the required beans at runtime.
  • Importance in Spring Boot:
    • Loose Coupling: DI decouples components, making it easier to modify or replace them without affecting other parts of the application.
    • Testability: DI allows you to easily mock dependencies during unit testing, improving the testability of your application.
    • Simplified Configuration: Spring Boot automatically handles dependency injection, reducing boilerplate code and improving development efficiency.
    • Better Maintainability: Changes to dependencies are centralized and don’t require changes to the dependent classes, leading to easier maintenance.

  • Example:

    @Service
public class UserService {
    private final UserRepository userRepository;

    // Constructor injection
    @Autowired
    public UserService(UserRepository userRepository) {
        this.userRepository = userRepository;
    }

    public void getUserDetails(Long userId) {
        userRepository.findById(userId);
    }
}

In summary, Dependency Injection is a core principle in Spring Boot that simplifies application development, enhances modularity, and promotes better design practices by managing dependencies automatically.