How to allow one user to acces resource

Hi Friends,

I am developing an web application in Servlet, My question is
if a person login to my application with user id(abc) and password(123456), if somebody tries open in same time with login with same user id(abc) and password(123456), my application should not allow him.

How can to do in servlet.

Thanks in Advance.
Santosh

Where ever you store your user information, I assume a database, add an in-use flag. I suggest making the flag an expiration timestamp, since the user may not sign off when they are done, and the profile will remain locked. This will also require your servlet to check that the user sign-on is still valid on each post.