Think of IoC as a shift in responsibility. Instead of your objects creating and managing their dependencies, the Spring framework takes over that job. It “injects” the necessary dependencies into your beans. This leads to more modular, testable, and maintainable code.
Here are a few ways Spring Boot demonstrates IoC:
- Constructor Injection
- Setter Injection
- Field Injection (Not Recommend) (Not recommend)
How Spring Manages IoC
Spring uses its Application Context (or WebApplicationContext in web applications) as a container to manage beans (objects). When your Spring Boot application starts:
- Spring scans your application for classes annotated with special stereotypes like
@Service,@Component,@Repository,@Controller, etc. These annotations tell Spring to manage these classes as beans. - For each bean, Spring analyzes its dependencies (through constructors, setters, or fields marked with
@Autowired). - Spring then creates and manages these dependencies, injecting them into the requesting beans.
Benefits of IoC
- Decoupling: Components become less dependent on the concrete implementations of their dependencies. They rely on abstractions (interfaces or abstract classes).
- Testability: It becomes easier to test individual components in isolation by providing mock or stub implementations of their dependencies.
- Maintainability: Changes in one component are less likely to affect other components.
- Reusability: Components become more reusable as they are not tightly coupled to specific implementations.
- Configuration: Dependency management is often externalized (e.g., through Spring configuration files or annotations), making it easier to change dependencies without modifying the code.