can one HttpSession object be used for more than one servlets
The session concept is closely tied to the idea of "web applications" - one web application can have many servlets which will all share the same servlet context and HttpSession. This is all covered in the servlet API.
Anybody doing servlet or
JSP coding should have a copy of the API,
which you can download from here. The API is designed so that multiple "web applications" can be hosted in a single server without interference or security problems.
Bill