How to redirect to Login page when Session is expired in Java web application?

Question

I'm running a web application in JBoss AS 5. I also have a servlet filter which intercepts all the requests to the server. Now, I want to redirect the users to the login page, if the session has expired. I need to do this 'isSessionExpired()' check in the filter and need to redirect the user accordingly. How do I do it?

Edit:

I'm setting my session time limit in web.xml, as below:

<session-config>
    <session-timeout>15</session-timeout>
</session-config>

Answer 1

Check for session is new.

HttpSession session = request.getSession(false);
if (!session.isNew()) {
  // Session is valid
}
else {
  //Session has expired - redirect to login.jsp
}

Answer 2

You could use a Filter and do the following test:

HttpSession session = request.getSession(false);// don't create if it doesn't exist
if(session != null && !session.isNew()) {
    chain.doFilter(request, response);
} else {
    response.sendRedirect("/login.jsp");
}

The above code is untested.

This isn't the most extensive solution however. You should also test that some domain-specific object or flag is available in the session before assuming that because a session isn't new the user must've logged in. Be paranoid!