How do I show home page if user has a valid session?

How do 开发者_如何学PythonI show a show home page if a user requests login page with a valid session using spring security?

if(session == null) {
   // not valid
} else {
   String username = (String) request.getParameter("username");
   String age = (String) request.getParameter("age");
}

When you load the login page, check for a valid session. If a valid session exists, then you can redirect the page to your home page. Where as if there is no session, you can continue with display of login screen.