Dinesh wrote:
> 
> i am making a chat server using servlet as server and applet as user
> interface, till now i had created multiple user single room chat. now i
> want to implement multiple room chat.

Use session management to track which room a user is in. Here are links to
session management information:

http://java.sun.com/docs/books/tutorial/servlets/client-state/index.html
http://www.servlets.com (look at examples for ch 7)
http://www.servletguru.com (download examples, look for examples in the
javaservlets/session package)