In any enterprise application, a common problem to handle is how to configure and wire together the different elements to achieve a business goal--for example, how to bind together the controllers at the web layer with the services and repository interfaces written by different members of the team without knowing about the controllers of the web layers. So, there are a number frameworks that provide a solution for this problem by using lightweight containers to assemble the components from different layers. Examples of such types of frameworks are PicoContainer and Spring Framework.

The containers of PicoContainer and Spring use a number of design patterns to solve the problem of assembling the different components of different layers. Here, I am going to discuss one of these design patterns--the dependency injection pattern. Dependency injection provides us with a decoupled and loosely coupled system. It ensures construction of the dependent object. In the following example, we'll demonstrate how the dependency injection pattern solves the common problems related to collaboration between the various layered components.