how to message from servlet and display in jsp

Question

I'm trying to do something that looks small but it's failing. I'm trying to send a response message back to a jsp when login fails but not being able. As of now I can only redirect back to the jsp but cannot display a message from the servlet on it. This is the servlet part of the redirection:

                if (count > 0) {
                res.sendRedirect("adminHome.jsp");
            } else {

                res.sendRedirect("index.jsp");
            }

I tried to print a message using PrintWriter and the redirect but failed because I couldn't get how to receive the message in the JSP. I also read that I shouldn't redirect but rather I should just forward from the servlet. How can I do this? Please help with the code patch to forward from servlet as well as that one to receive in JSP. Thanks

Answer 1

If you insist to use redirect instead of forward, then you have 2 options:

1. Pass the message as request parameter

   String message = "hello";
   res.sendRedirect("adminHome.jsp?message=" + URLEncoder.encode(message, "UTF-8"));
   

   so that you can display it in JSP as follows

   <p>Message: ${param.message}</p>
   

   It's only visible in the browser address bar as well and you aren't able to pass non-standard Java objects this way.

2. Store it in session

   String message = "hello";
   req.getSession().setAttribute("message", message);
   res.sendRedirect("adminHome.jsp");
   

   so that you can display (and remove) it in JSP as follows:

   <p>Message: ${message}</p>
   <c:remove var="message" scope="session" /> 
   

   Removing is important, otherwise it sticks there for the entire session.

---

However, if you're open to using forward instead of redirect, it's more elegant:

String message = "hello";
req.setAttribute("message", message);
req.getRequestDispatcher("/adminHome.jsp").forward(req, res);

and display it as follows in JSP

    <p>Message: ${message}</p>

See also:

• Our Servlets wiki page - contains a Hello World which also treats messaging
• EL wiki page - explains all about those ${} things.

Answer 2

Set your message as an attribute of the request object:

request.setAttribute("message", messageString);

Use a RequestDispatcher to dispatch the request and response objects to the jsp:

RequestDispatcher dispatcher = getServletContext().getRequestDispatcher("urlString");
dispatcher.forward(request, response);

Access it in your JSP using Expression Language syntax:

${message}