puzzle for everyone

Hi,
From last few weeks i working on online exam problem..
rest of the things are all ok..
but i m sufferring with a big problem..
i m creating a session for each user and it's working fine..
At the end i invalidating a session for that user and i m
inserting his marks into database...
upto this is very fine..
next time when i again start the exam the first question is
always the old one and if i click on next question (Without
refreshing )i get NullPointerException prbably because of
the previous exam object has been invalidated.
i m creating Exam object in doGet method ..
and further processing is in
but at the first question if i refreshed program works smoothly
so i think this might be a problem of cache memory ..
can anybody please help me???
i m using resin server...
Bhupendra

Pl. do not post your question more that once.
Your earlier post din't get any responses, because,
IMO its too specific could you re-phrase it and post
in the same thread.
Also, If I could suggest one more thing, please use
appropriate subjects something like "NullPointer Exception
using Resin". This way anyone who knows Resin will definetly
look at your post and have some suggestions. I agree that
its a little dis-heartning when no one replies.

But then we should try our best.
We appreciate your cooperation.
Thanks.

- satya