Hi,
controller part is developed by servlet components. whenever client make a request,
front controller used to identify the request and give to the specific request processor which is used to handle request by doing the following..
protocal handling, form validation, action mapping,....etc
and give the request to the action and take the response give the response to the view.

front controller is one servlet component provided by framework.
request processor (application controller) is one servlet provided by framework.
action is one servlet developed by us.

thanks