Dependency Injection (DI) is a fundamental aspect of the Spring framework, through which the Spring container "injects" objects into other objects or "dependencies". In other words, DI is a design pattern that removes the dependency from the programming code so that it can be easy to manage and test the application. The Spring-Core module is responsible for injecting dependencies through either Constructor or Setter methods. The benefits of using DI in Spring include:

• Loose coupling: Dependency Injection makes our programming code loosely coupled. Loose coupling between classes can be possible by defining interfaces for common functionality, and the injector will instantiate the objects of required implementation.

• Ease of testing: One of the major benefits of dependency injection in Spring is the ease of having mock service classes rather than using actual services. DI makes the code easier to test and reuse.

• Flexibility: DI provides flexibility, with the open-source RAD platform enabling fast development of business applications.

• Good software design: DI adheres to the design principle of Inversion of Control, which emphasizes keeping the Java classes independent of each other and the container frees them from object creation and maintenance.

In Spring, there are two types of DI: constructor injection and setter injection. Constructor injection is where the Spring container injects dependencies through a constructor, while setter injection is where the Spring container injects dependencies through a setter method.