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How getServlet request dispatcher by URL?

I need to populate some request with data and redirect back. Is there Spring RedirectAttributes analog for Java EE? I have searched and found 2 solutions, but they also have limitation:
Response.sendRedirect()
In this case I will lost all destroys request attributes. I can use Session attributes but in this case I need some mechanism that can determine when redirect comes in or when there is no redirect and data must be removed.
getRequestDispatcher(String path).forward(request,response)
The problem with path - I need to send redirect to URL not to give something jsp or Servlet by name. Is there any way to "convert" redirect URL to path? For example how I can go forward to
"http://localhost:8080/WebAppname/"?

You can use the sendRedirect and pass the parameters as part of the query string. So what you would be redirecting can be something like below
http://localhost:8080/WebAppname/myRedirect.action?param1=value1&param2=value2

Multiple Request Response Forward

I am currently passing some ArrayList's from my servlet to my JSP page using the below code.
RequestDispatcher rd = null;
request.setAttribute("date",al);
request.setAttribute("bau",al1);
request.setAttribute("project",al2);
rd = request.getRequestDispatcher("ResourceChart.jsp");
rd.forward(request,response);
The problem is when I click refresh on the page, the same date is passed again and I end up with odd results. Should I be forwarding to the JSP page as well to avoid the servlet regenerating the variables and passing them?
Whats the best way to implement this?

You're apparently refreshing a POST request and ignoring/confirming the browser's builtin warning that the data would be resent. In that case, the doPost() method will indeed be re-executed with the previously submitted data which would only end up in duplicate entries in the DB.
The canonical approach to avoid the double submit on a refresh of a POST request is to send a redirect after POST request. A redirect implicitly creates a new GET request. Refreshing would then result in only the GET request being re-executed which is totally harmless.
To achieve that, replace all in the question shown lines of the doPost() by the following single line
response.sendRedirect(request.getContextPath() + "/ResourceChart");
(assuming that your servlet is mapped on an URL pattern of /ResourceChart)
and create a new doGet() method wherein you put all those removed lines back, along with the necessary logic to prepare the lists. The only change which you need to make is to put the JSP file in /WEB-INF folder to avoid endusers from being able to open it directly by entering/guessing its URL without calling the servlet's doGet() first.
request.getRequestDispatcher("/WEB-INF/ResourceChart.jsp").forward(request, response);
See also:
Our Servlets wiki page

Java Servlets, how to keep request attribute alive across several forwards?

I have a home-grown MVC implementation. A ControllerServlet like so:
/controller?cmd=EditUser&userid=55
From this URL, the controller creates a EditUserCommand.class instance and calls an execute() method which returns the result page (ex. user.jsp) to display.
The controller servlet then does a ...
getRequestDispatcher(resultPage).forward(request, response);
... and the resulting page is shown.
One of the things the controller does is set messages (error, info, and so on) as request attribtues. For example:
request.setAttribute("infoMessage", "User was edited successfully.");
And that message gets pulled out of the request in the user.jsp page and displayed.
Works fine.
Now here comes my problem.
Sometimes my commands don't return a page like user.jsp but return a URL like cmd=ShowUser&userid=55 for the result. This is because there might be things I want to check before displaying the final page, like permission to view the user and so on.
When I do this the "infoMessage" I placed in the request never appears because the result is a URL that makes a new call to the servlet, which is a new request. The new request doesn't maintain the request attributes from the first request; which makes sense, I just didn't forsee this happening.
How can I make my request variable "stay alive" until it's actually displayed on the final page that results from the original request?
Any suggestions or advice are appreciated. Just FYI, I can't re-write the entire app to go to something like Struts, Spring MVC, of JSF. It's not an option.
Thanks!
Rob

redirect generally looses request data because of brand new request from browser. One possible approach may be append your message to url string as attribute and read it when you need.
Based on your EDIT: After your edit also, my answer make sense. But, only one correction is, it is not brand new request because forward happens on server side.

Have you tried using a RequestDispatcher instead of a Redirect?
RequestDispatcher dispatcher = request.getRequestDispatcher("/myNextPage.jsp");
dispatcher.forward(request, response);

You may be giving a simple example, but your control flow causes the "Resend" Error, perhaps? Basically, after making any change to the data, the controller must immediately do a "Get" via a redirect and the screen should be displayed completely stateless.
Please take a look:
http://en.wikipedia.org/wiki/Post/Redirect/Get
As such, Attributes are not a great help. What you may want to consider is, maintaining a Bean/Object for every login user, and persist this object in a LRU cache (JCache or MemcacheD), and retrieve it on every entry to the application. Once you have that, you can maintain a pseudo-state such as previous results in that object.
In any case, using Attributes to retain state will severely constrain your options. You need to have a more generic flexible routing-independent mechanism.

Java Servlet Behaviour Question

I am currently implementing an OpenID Relying Party (RP) and Identity Provider (IdP) with Java HttpServlets using the OpenID4Java library. I have run into trouble getting two servlets to communicate with each other. I believe the problem I am having is to do more with how Servlets behave, however I have included info about my application for a better sense as to what is happening.
The scenario is as follows:
Servlet #1 (my RP) sends a request to Servlet #2 (my IdP) as follows:
httpResp.sendRedirect(authReq.getDestinationUrl(true));
Essentially authReq = a message with various OpenID specific parameters. By invoking getDestinationUrl(true) it encodes the request into a url to send via a GET.
Servlet #2 catches the above GET in its doGet method. It parses the information, and crafts a reply to send back to Servlet #1 in the following fashion:
String responseText = processRequest(httpReq, httpResp);
httpResp.setContentType("text/html");
OutputStream outputStream = httpResp.getOutputStream();
//
outputStream.write(responseText.getBytes());
outputStream.close();
My problem is, this response never makes it back to Servlet #1. I would expect that when Server #1 receives the response from Servlet #2 that its' doGet or doPost method would catch the message. However neither case happens.
Any advice would be greatly appreciated.
Thanks!

The response of 2nd servlet will directly go on client side i think because its is the original client right? Your 1st servlet is just redirecting the request.
So, if you want to communicate between servlets, Use URLConnection or Apache HttpClient to communicate with 2nd servlet.
You can also make JSP instead of 2nd servlet, then pass you data from 1st servlet to that JSP. That JSP's response will be sent to client then. After all you can do all logic in JSP what you can in servlet.
Hope this helps.
parth.

If you want two servlets to communicate with each other within an application, you can use the ServletContext object and share data via ServletContext.setAttribute and ServletContext.getAttribute and RequestDispatcher obtained via HttServletRequest or ServletContext
In your case can the Servlet#2 be invoked directly by the client? If not then you should probably refactor the processRequest(request, response) into a Utility class or a library. Which in turn can be called by both Servlet#1 and Servlete#2.
response.sendRedirect sends a redirect (301 moved permenently, ithink) to the browser. So your servlet actually sends a response to browser with 301 and then browser makes a request to servlet#2 again.

You can use RequestDispatcher to include your second servlet's response. In this way, the control returns to the first servlet after the method completes.
RequestDispatcher dispatcher = request.getRequestDispatcher(authReq.getDestinationUrl(true));
dispatcher.include(request, response);
However, with this, the response generated by the called servlet will be sent to the browser. If you want your calling servlet to capture the message from called servlet without sending to browser, you can either create a response wrapper (A wrapper writing the contents in a string) and pass this wrapper when you include the second servlet or better you can share the data in either of the scopes (Preferably 'request' scope): You can set the data in the request scope in called servlet and you can retrieve it in the calling servlet after include() completes.
When you redirect, you are telling the browser to make a new request for the URL. So there will be new request/response objects created as if you had clicked on a link in your page.
Hope this helps.

Configure Restlet to Return JSPs on Google App Engine?

I have a developed a Restlet application. I would like to return a JSP file on a URL request through Restlet. How can I achieve this without using a redirect?
i.e.
Let's say I have the file "contact.jsp" on mydomain.com and I want people to be able to access contact.jsp at http://mydomain.com/contact
Thus, in Restlet, I would have:
router.attach("/contact", MyResource.class);
But how can I return the "contact.jsp" page? I know that a redirect would work, but I don't want users to see the ".jsp" in "http://mydomain.com/contact.jsp"... or is there another strategy that would work without even using restlet? Maybe some modification of my web.xml file?
Edit (2009-08-14):
My answer posted below doesn't work on App-Engine and Restlet. It does work however, if I don't include Restlet, or allow Restlet to have a url-pattern of "/*"
What would be ideal is to have a subclass of the Router that allows me to do this:
router.attach("/contact", "/contact.jsp");
Thanks!
Edit (2009-08-17):
I'm surprised I haven't had any responses since I posted a bounty. Will someone comment and let me know if my question/problem isn't clear?
Edit (2009-08-17):
Interesting observation. When using the method described by "Rich Seller" below, it works when deployed on Google App-Engine and not locally. Additionally, If I call http://mydomain.com/contact.jsp on Google App-Engine it bypasses Restlet and goes straight to the JSP. But, locally, Restlet takes over. That is, http://localhost:8080/contact.jsp does not go to the JSP and goes to Restlet. Do deployed app-engine applications respond differently to URLs as their local counterpart?

Restlet doesn't currently support JSPs directly. They're difficult to handle outside of the servlet container.
There's a discussion on Nabble about this issue that you may find useful, at the moment it looks like you need to either return a redirect to the JSP mapped as normal in the web.xml, or hack it to process the JSP and return the stream as the representation.
The response dated "Apr 23, 2009; 03:02pm" in the thread describes how you could do the hack:
if (request instanceof HttpRequest &&
((HttpRequest) request).getHttpCall() instanceof ServletCall) {
ServletCall httpCall = (ServletCall) ((HttpRequest) request).getHttpCall();
// fetch the HTTP dispatcher
RequestDispatcher dispatcher = httpCall.getRequest().getRequestDispatcher("representation.jsp");
HttpServletRequest proxyReq = new HttpServletRequestWrapper(httpCall.getRequest());
// Overload the http response stream to grab the JSP output into a dedicated proxy buffer
// The BufferedServletResponseWrapper is a custom response wrapper that 'hijacks' the
// output of the JSP engine and stores it on the side instead of forwarding it to the original
// HTTP response.
// This is needed to avoid having the JSP engine mess with the actual HTTP stream of the
// current request, which must stay under the control of the restlet engine.
BufferedServletResponseWrapper proxyResp = new BufferedServletResponseWrapper(httpCall.getResponse());
// Add any objects to be encoded in the http request scope
proxyReq.setAttribute("myobjects", someObjects);
// Actual JSP encoding
dispatcher.include(proxyReq, proxyResp);
// Return the content of the proxy buffer
Representation rep = new InputRepresentation(proxyResp.toInputStream(),someMediaType);
The source for the BufferedServletResponseWrapper is posted a couple of entries later.

"I would like to return a JSP file on a URL request through Restlet" - My understanding is JSP's are converted to servlets. Since Servlets are orthogonol to Restlets not sure how you can return JSP file through Restlet.
Assuming you are asking for a way to use JSP in addition to Restlet, This is best achieved by mapping your restlets to a rootpath such as /rest instead of /* and using the .jsp as usual.

Looks like a simple web.xml configuration.
<servlet>
<servlet-name>contactServlet</servlet-name>
<jsp-file>/contact.jsp</jsp-file>
</servlet>
<servlet-mapping>
<servlet-name>contactServlet</servlet-name>
<url-pattern>/contact</url-pattern>
</servlet-mapping>
This works without Restlet in App-Engine. But once I include Restlet, it doesn't work if I set my Reslet url-pattern to "/*"