Hi,
First af all, Servlet is an interface, and HttpServlet is a class.
In general javax.servlet package has all the classes/interfaces not directly tied to HTTP, and java.servlet.http package has the classes/interfaces that deals with the http protocol.
If you are going to use HTTP,
you should extend the class HttpServlet (wht you normally do). If you are not going to use HTTP, you can extend just GenericServlet, that implements the generic interface Servlet, but it is not tied to HTTP.
Dani