Java EE (Java Enterprise Edition) General Discussion

Hi,
I am facing the problem when redirecting to a jsp from another jsp.

I have one loginscreen .jsp which redirects to another jsp index.jsp
for example

http://c8160.mns.co.in:7001/Authn/LoginScreen.jsp?redirectURL=http://c8160.mns.co.in:7001/lmn/Index.jsp

here my client is removing the "redirectURL=http://c8160.mns.co.in:7001/lmn/Index.jsp" ,placing the javascript code <script>alert("hi")</script>

which leadind to application failure.

Pls anyone suggest how i can prevent the client to modify this .(like when modify this disaplying the error message or making session expired like that)