Hi Manish, i think understand what you want to say.. Next time specify
problem in some detail and clear form.

You can developed a web application in which mainly three layer are
present namely View (Jsp files),
Controller(Servlets files), Model(Plain Java file for managing
business logic and database mapping).
For example :
You can create a jsp page let home.jsp Now, forward request from this
jsp file to servlet ,servlet handle the request by approriate
method(doGet(),doPost()), inside these method call business logic
and
data from data base and send to a new jsp page let say result.jsp.

Now comes to your main question here jsp is front end which intract
with user.
servlet is controller or middle layer, model(business logic or data
access classes) are third layer  or say business logic or dataaccess
layer

i'm v. sorry for manish intead of Manisha chawla...