What are Dependency Injection (DI) and Inversion of Control (IoC) in Spring?

The following article describes Dependency Injection (DI) and Inversion of Control (IoC).

In fact, Dependency Injection and Inversion of Control are two core concepts in the Spring Framework that enable loosely coupled and highly modular application design.

Actually, Dependency Injection enables the separation of an object’s creation and its dependencies. Hence, it allows for more flexible and reusable code. In the context of the Spring Framework, DI means that an object’s dependencies are “injected” into it at runtime by an external entity, such as the Spring container, rather than being explicitly instantiated by the object itself. So, this approach promotes decoupling and modular design. Because, it allows the testing and development of objects in isolation, without having to worry about creating or managing their dependencies.

On the other hand, IoC is a broader design principle that underlies DI. Basically, IoC means that rather than the application code controlling the flow of the application, the control is inverted or delegated to an external entity. In the context of the Spring Framework, the external entity responsible for controlling the flow of the application is the Spring container, which manages the instantiation and lifecycle of objects and their dependencies. So, by delegating control to the container, the application code can focus on its core business logic. While the container takes care of the underlying infrastructure.

In summary, together, DI and IoC promote modular, flexible, and testable code by enabling loose coupling and separation of concerns. Furthermore, we achieve DI and IoC through the use of interfaces, annotations, and XML configuration files that define the dependencies of an object and how they should be managed by the container.

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