Java Filter to redirect users who are not logged in to login page

Question

I was trying to make a filter to stop users who are not logged in from accessing certain pages.For this i made a filter class with the following doFilter method

HttpServletRequest request = (HttpServletRequest) req;
HttpServletResponse response = (HttpServletResponse) res;
String url = request.getRequestURI();
boolean allowedRequest = false;

System.out.println(url);

if(urlList.contains(url)) {
    allowedRequest = true;
    System.out.println("in list");
}

if (!allowedRequest) {
    Object o = request.getSession().getAttribute("UserInfo");
    if (null == o) {
        System.out.println("Hey i am in");
        response.sendRedirect("/login.jsp");
    }
}

chain.doFilter(req, res);

} // end of doFilter

To allow the pages which doesnot need the user to be logged in i created an arraylist url-list in init()

Now a very strange stupid thing is happening. suppose i have two pages home.jsp and dcr.jsp. When i try to access home.jsp without logging in the i am successfully redirected to login.jsp but when i am trying to access dcr.jsp it is not redirected although it enters the loop if(null == o) which i can understand because i am getting that line printed in console.THis is the output that i get in the server This is the output that i get in the server

/dcrmaintenance.jsp

Hey i am in

Which tells me that the null == o was true.

The page dcr.jsp accesses a session object and since the user is not logged in it is getting java.lang.NullPointerException as expected but i cannot understand why is the redirection not taking place even after entering the loop.If someone can pt out where i am making a mistake it would be appreciated.

Answer 1

After response.sendRedirect("/login.jsp"); do return;.

Answer 2

I believe that you should either invoke sendRedirect OR doFilter. E.g.

if (requiresLogin)
  response.sendRedirect("/login.jsp");
else
  chain.doFilter(req,resp);