Introduction to IOC (Inversion Of Control)/ DI (Dependency Injection)

Originally, dependency injection was commonly referred to by another name: inversion of control.

When applying DI, objects are given their dependencies at creation time by some external entity that coordinates each object in the system. In other words, dependencies are injected into objects. So, DI means an inversion of responsibility with regard to how an object obtains references to collaborating objects .

The key benefit of DI is loose coupling. If an object only knows about its dependencies by their interface (not their implementation or how they were instantiated) then the dependency can be swapped out with a different implementation
without the depending object knowing the difference.

The org.springframework.beans.factory.BeanFactory is the actual representation of the Spring IoC container that is responsible for containing and managing beans.
The BeanFactory interface is the central IoC container interface in Spring. Its responsibilities include instantiating or sourcing application objects, configuring such objects, and assembling the dependencies between these objects.
The most commonly used BeanFactory implementation is the XmlBeanFactory class. This implementation allows you to express the objects that compose your application, and interdependencies between such objects, in terms of XML. The XmlBeanFactory takes this XML configuration metadata and uses it to create a fully configured system or application.

In Spring frameowork, Dependency Injection (DI) design pattern is used to define the object dependencies between each other. It exits in two types :

• Setter Injection
• Constructor Injection