Front controller

Front controller
1. The controller is the initilal contact point for handling all the requests in system,
2. The controller actually is a centralized access point for presentation tier request handling, if the user access the view(like jsp files) without going through a centralized point. it may lead to problems, that the each view is required to provide its own system services, resulting in duplicate code.for example: in thr front controller,
2.1.we can dispatch the request to delegate tier to handle special business logic,
2.2.we can directly forward the request to view tier