My session objects are only stored within the request scope on google app engine and I can't figure out how
to persist objects between requests. The docs are next
to useless on this matter and I can't find anyone who's experienced a similar problem. Please help.
When I store session objects in the servlet and forward the request
to a JSP using:
getServletContext().getRequestDispatcher("/example.jsp").forward(request,response);
Everything works like it should. But when I store objects
to the session and redirect the request using:
response.sendRedirect("/example/url");
The session objects are lost
to the ether. In fact when I dump session key/value pairs on new requests there is absolutely nothing, session objects only appear within the request scope of servlets which create session objects. It appears
to me that the objects are not being written
to Memcache or Datastore.
In terms of configuring sessions for my application I have set
<sessions-enabled>true</sessions-enabled>
In appengine-web.xml. Is there anything else I am missing?
The single paragraph of documentation on sessions also notes that only objects which implement Serializable can be stored in the session between requests. I have included an example of the code which is not working below.
The obvious solution is
to not use redirects, and this might be ok for the example given below but some application data does need
to be stored in the session between requests so I need
to find a solution
to this problem.
EXAMPLE: The class FlashMessage gives feedback
to the user from server-side operations.
if (email.send()) {
FlashMessage flash = new FlashMessage(FlashMessage.SUCCESS, "Your message has been sent.");
session.setAttribute(FlashMessage.SESSION_KEY, flash);
// The flash message will not be available in the session object in the next request
response.sendRedirect(URL.HOME);
} else {
FlashMessage flash = new FlashMessage(FlashMessage.ERROR, FlashMessage.INVALID_FORM_DATA);
session.setAttribute(FlashMessage.SESSION_KEY, flash);
// The flash message is displayed without problem
getServletContext().getRequestDispatcher(Templates.CONTACT_FORM).forward(request,response);
}
FlashMessage.java
import java.io.Serializable;
public class FlashMessage implements Serializable {
private static final long serialVersionUID = 8109520737272565760L; // I have tried using different, default and no serialVersionUID
public static final
String SESSION_KEY = "flashMessage";
public static final
String ERROR = "error";
public static final
String SUCCESS = "success";
public static final
String INVALID_FORM_DATA = "Your request failed
to validate.";
private
String message;
private
String type;
public FlashMessage (String type,
String message) {
this.type = type;
this.message = message;
}
public
String display(){
return "<div id='flash' class='" + type + "'>" + message + "</div>";
}
}
