What is need of method injection
When a singleton Bean needs to communicate with prototype Bean then it becomes difficult to handle by container as The container will only create the singleton bean A once, and thus only get the opportunity to set its properties once. There is no chance for the container to provide bean A with a new instance of bean B every time one is needed.
This problem can be solved by implementing BeanFactory Aware by Bean a, But that is not a good solution. So Method Injection, an advanced feature of the Spring IOC framework allows solving the problem in a clean and fashioned way.