Clean β’ Professional
Spring Frameworkβs core is built around Inversion of Control (IoC) and Dependency Injection (DI). These concepts help manage object creation, dependencies, and lifecycle, making your applications modular, maintainable, and easy to test.
Inversion of Control is a principle where the control of object creation, configuration, and lifecycle is transferred from your application code to the Spring container.
Instead of manually creating objects using the new keyword, Spring handles this for you.
Purpose:
Analogy:
Imagine ordering a meal at a restaurant. You donβt cook it yourself; the chef (Spring container) prepares it. Similarly, Spring manages your objects.
Example Without IoC:
public class UserService {
private UserRepository repo = new UserRepository();
}
UserService is tightly coupled to UserRepository.UserRepository.Example With IoC (Spring manages objects):
@Component
public class UserService {
private final UserRepository repo;
@Autowired
public UserService(UserRepository repo) {
this.repo = repo; // Spring injects dependency
}
}
UserRepository.UserService no longer controls instantiation.Dependency Injection is a design pattern that implements IoC. It allows Spring to provide the required dependencies to a class instead of the class creating them itself.
Purpose:
How It Works:
Spring injects dependencies into your class using one of three main ways:
Dependencies are provided via the constructor. Best for mandatory dependencies.
@Component
public class OrderService {
private final PaymentService paymentService;
@Autowired
public OrderService(PaymentService paymentService) {
this.paymentService = paymentService;
}
}
Dependencies are provided via setter methods. Useful for optional dependencies.
@Component
public class OrderService {
private PaymentService paymentService;
@Autowired
public void setPaymentService(PaymentService paymentService) {
this.paymentService = paymentService;
}
}
Dependencies are injected directly into fields using @Autowired.
@Component
public class OrderService {
@Autowired
private PaymentService paymentService;
}

| Concept | Definition | Example / Benefit |
|---|---|---|
| IoC | The principle where Spring container controls object creation, configuration, and lifecycle | Reduces coupling, easier testing |
| DI | The technique used to inject dependencies into classes | Flexible, modular, maintainable code |
| Types of DI | Constructor, Setter, Field | Constructor injection is preferred for mandatory dependencies |
Visual Concept:
[Your Class] <--- DI --- [Dependency provided by Spring Container]
^
|
IoC Principle: Container controls object creation & lifecycle
IoC and DI are the foundation of Spring Framework.
Using these concepts ensures your Spring applications are scalable, maintainable, and professional-grade, and provides a solid foundation for REST APIs and enterprise applications.