What is Dependency Injection and Inversion of Control in Spring Framework?

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  • Spring helps in the creation of loosely coupled applications because of Dependency Injection.
  • In Spring, objects define their associations (dependencies) and do not worry about how they will get those dependencies. It is the responsibility of Spring to provide the required dependencies for creating objects.

For example: Suppose we have an object Employee and it has a dependency on object Address. We would define a bean corresponding to Employee that will define its dependency on object Address.

When Spring tries to create an Employee object, it will see that Employee has a dependency on Address, so it will first create the Address object (dependent object) and then inject it into the Employee object.

  • Inversion of Control (IoC) and Dependency Injection (DI) are used interchangeably. IoC is achieved through DI. DI is the process of providing the dependencies and IoC is the end result of DI. (Note: DI is not the only way to achieve IoC. There are other ways as well.)

  • By DI, the responsibility of creating objects is shifted from our application code to the Spring container; this phenomenon is called IoC.

  • Dependency Injection can be done by setter injection or constructor injection.

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