JSP Session.getAttribute() value return null

Question

I have no idea why my session.getAttribute("user") return not null but attribute value retun null after few minutes, it might due to session time out but why only the attribute value return null but other session still there even session.getAttribute("user") return not null.

This is my web page flow, User Login

LoginServlet

User s = new User();
s.retriveuser();
session.setAttribute("balance", s.getBalance());
session.setAttribute("username", s.getUsername());
session.setAttribute("user", s);

My Profile

        User user = new User();
        if (session.getAttribute("user") == null) {
            response.sendRedirect("login.jsp");
        } else {
            user = (model.User) session.getAttribute("user");
        }

 <tr>
         <th>Gender:</th>
              <td><%=user.getGender()%></td>
 </tr>
 <tr>
         <th>Name:</th>
         <td><%=user.getName()%></td>
 </tr>

It can display after the user login everything work fine, after few minutes the gender name ... will display null instead of redirect to login page. And my balance and username session still there. Before setting else user = (User) session.getAttribute("user"); I was using

<jsp:useBean id="user" class="model.User" scope="session" />

Answer 1

I have no idea why my session.getAttribute("user") return not null but attribute value retun null after few minutes

Ok, so attribute "user" becomes null.

it might due to session time out but why only the attribute value return null but other session still there even session.getAttribute("user") return not null.

Que?? So attribute "user" is not null??

There are only two possibilities for changing session attributes:

1. If your session times out: all attributes are cleared by the container at the same time.
2. If your session does not timeout, and only one of your attributes is cleared: one attribute was cleared by your program.

Extra Note A: from javadoc for HttpServletResponse.sendRedirect: After using this method, the response should be considered to be committed and should not be written to. Your code above violates this.

Extra Note B:

   User user = new User();

You just populated it with a rubbish new, empty user object. Avoid that - it's a bug waiting to happen. Only set variables to useful/valid values. :)

Answer 2

What have you been using inside the bean code? Are you sure you have made an empty constructor, getters, setters, that the java class implements Serializable?Then, on the jsp page it's better that you use <jsp:setProperty name="the_same_you_used_in_bean_id" property="*"/>. If you want some more info about the bean structire, let me know!

Answer 3

I don't readily have access to test this out. But I am guessing the user object is not created in the session, hence does not get set to null.

if (session.getAttribute("user") == null) {
            response.sendRedirect("login.jsp");
            user=null;
} else {
    user = (model.User) session.getAttribute("user");
}

Should solve your problem.

Edit Also, simply printing user.Gender() will return Null in this case, so you're better off printing it straight from the session variable.