Form Based Authentication

Hi,
I am using form based authentication, running tomcat web server.

What i need is to know when any user authenticates himself correctly.
Is there any listener i can define.
Because so far i only know when user fails to authenticate (sent to error page) or when he tries to authenticate (thus i present the login page)

I want to know when the j_security_check was called successfully.

Thanks

I am new to servelts.How Can I create Login page in servlets using MYSQL