CODEWITHSUNDEEP
javagoogle-app-enginejspservlets
Legend
Legend

Reputation: 116850

JSP::Confused with the session objects

I just started exploring Java Servlets and JSP and am a little confused about the sessions object. Inside a servlet I have this:

public class SampleServlet extends HttpServlet {

    public void doPost(HttpServletRequest request, HttpServletResponse response)
    throws IOException {

        HttpSession session = request.getSession(true);
        session.setAttribute("_session", "_value");
                response.sendRedirect("page2.jsp");         
        }
}

Now, inside page2.jsp, there is a session object as well, but when I do this

<%
out.print(session.getAttribute("_session"))
%>

it does not seem to get the value (as if it is not set). I tried setting a boolean attribute to true but in the jsp page it returns a false. Can someone tell me the right way of doing this? As to what I am trying to do, I want to share some session variables.

Upvotes: 3

Views: 3130

Answers (3)

BalusC
BalusC

Reputation: 1108782

Although not the best approach (I'd rather use EL ${_session} than a scriptlet), this should work fine. Your problem lies somewhere else. Are you running the code you think you're running? How are you compiling and deploying the code? Didn't you trim too much off from the given example? The session is namely domain and context dependent, if you redirect to a different domain and/or context, then a new session would be created. Also, the session is backed by a cookie, does the browser have cookies enabled? Else you'll have to use HttpServletResponse#encodeRedirectURL() to append the session identifier to the redirect URL.

response.sendRedirect(response.encodeRedirectURL("page2.jsp"));

Update: to debug if it's really the same session, do in the servlet:

System.out.println("Session ID: " + session.getId());

and in the JSP:

<p>Session ID: ${pageContext.session.id}</p>

Also installing a HTTP header tracker like Firebug's Net panel may bring new insights. The HTTP response should include a Set-Cookie header with the session ID and the subsequent HTTP requests should include a Cookie header with the same cookie name/value, usually JSESSIONID with a long hex value like as on this screenshot.

Update 2: since I was suprised because a forward apparently fixes this issue, I tried to reproduce this on Tomcat 6 and Glassfish 3, but this approach works perfectly on the both servers. So I suspect a bug in the container used by Appengine, that it is not setting the cookie correctly during the redirect.

As evidence, here's a screen which proves that Glassfish is setting the cookie by Set-Cookie and firing the redirect by Location:

alt text

Upvotes: 1

Matthew Flynn
Matthew Flynn

Reputation: 2238

Use request.getRequestDispatcher().forward() instead of response.sendRedirect();

So your code would be:

 HttpSession session = request.getSession(true);
 session.setAttribute("_session", "_value");
 request.getRequestDispatcher("page2.jsp").forward();

Basically, response.sendRedirect() does not preserve session info, so it's not there when the jsp gets it. request.forward() does preserve the session.

See http://www.coderanch.com/t/170618/java-Web-Component-SCWCD/certification/sendRedirect-Vs-requestdispatcher-forward

Upvotes: 4

Matt Ball
Matt Ball

Reputation: 359836

Assuming your container supports it, use EL!

Java side:

HttpSession session  = request.getSession(true);
session.setAttribute("foo", "bar");

JSP side:

<html>
    ...
    <body>
        ...
        <p>${foo}</p>
        ...
    </body>
</html>

And that will give you a paragraph containing the string bar.

Upvotes: 1

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