Can you explain the key principles on which the Spring framework is based?

Spring is a popular Java framework based on several key principles:

• Inversion of Control (IoC): the creation and binding of objects are managed by the Spring container rather than manually in the code. This makes dependency management easier.

• Dependency Injection (DI): objects receive their dependencies from outside, usually through constructors or setters, which increases modularity and testability.

• Aspect-Oriented Programming (AOP): allows separation of cross-cutting concerns (e.g., logging, transactions) from business logic, improving code readability and maintainability.

• Modularity and Extensibility: Spring consists of many modules (e.g., Spring MVC, Spring Data) that can be used separately or together.

• Configuration via annotations and XML: supports flexible component configuration.

Example of dependency injection using annotations:

@Component
public class UserService {
    private final UserRepository userRepository;

    @Autowired
    public UserService(UserRepository userRepository) {
        this.userRepository = userRepository;
    }
    // business logic
}