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Hiding Parameters in url while sending url through response.sendRedirect method

I am sending url to another server through response.sendRedirect() method and it is generating pdf for me. I am passing all the parameters but one of the parameter data is exceeding length due to which browser is not able to handle it and request is getting blocked.
I know through Post method we can hide url Parameters and response.sendRedirect() uses GET method. Is there any POST method like sendRedirect through which we can access another server url directly through servlet? Thanks in advance.

With response.sendRedirect(newUrl) you send back a HTTP status 302 with a new Location=newUrl in response header. Thus, you cannot force browser to make POST instead of GET method.
What you could do is to consume a pdf file from within your server code and return it to the client, hiding thus from client the actual target location. You can then build any request with method and parameters you want to the new location if it accept it.
See, for example, this tutorial how to make a request to another server from your servlet http://www.mkyong.com/java/how-to-send-http-request-getpost-in-java/

what is in background of html submit form?

I'm trying to figure out what really happens when html submit form button is clicked.
I suppose it generates some kind of http request (similar to ajax get or post call) which has data in http body and is sent to address specified in action field.
1) Am I right?
2) I've seen many ways of processing forms with PHP or ASP on server side. Can I process it with Java REST Application using e.g. Jersey? Is submit form capable of hitting REST if I put right URL in action field?
Thank You.

By submitting the form in HTML you basically tell the browser to generate a normal HTTP request, usually POST or GET, for an URL defined in tag with form fields attached according to the specified method either appended to the URL or included in the request data.
There is nothing really special or different from a "normal" HTTP request, in fact you can manually "submit a form" by appending form keys and values to the URL in your browser and navigating to it in case of GET method.
Summarizing:
1) Yes, you are right.
2) From what I've just read (never used REST personally) a REST application is implemented by a servlet mechanism and uses HTTP protocol, so it should be possible to write a REST application for processing HTML forms if the form points to this application's URL.

Getting response from servlet. ExtJs

I have a extJs form with fileupload and servlet. After uploading file i want to get response from servlet.
i do this System.out.println("{success:true, error:'error'}");
But in firebug in POST i dont see anything. This code works in case wiht jsp but not servlet. So how to send parametrs from servlet?

System.out PrintStream is not the the output stream of your servlet response. It is still the "standard" system out stream. Most application servers redirect that to a log file.
Servlet's service() method, as well as do*() methods of HttpServlet, take ServletResponse respectively HttpServletResponse as a parameter. When implementing a servlet, one can call getWriter() on that parameter to get a PrintWriter open on response's output stream. That can be used to print something to the response.
So, your code should be something like:
response.getWriter().println("{success:true, error:'error'}");

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.

AS2: Does xml.sendAndLoad use POST or GET?

All,
I'm trying to find out, unambiguously, what method (GET or POST) Flash/AS2 uses with XML.sendAndLoad.
Here's what the help/docs (http://livedocs.adobe.com/flash/9.0/main/wwhelp/wwhimpl/common/html/wwhelp.htm?context=LiveDocs_Parts&file=00002340.html) say about the function
Encodes the specified XML object into
an XML document, sends it to the
specified URL using the POST method,
downloads the server's response, and
loads it into the resultXMLobject
specified in the parameters.
However, I'm using this method to send XML data to a Java Servlet developed and maintained by another team of developers. And they're seeing log entries that look like this:
GET /portal/delegate/[someService]?svc=setPayCheckInfo&XMLStr=[an encoded version of the XML I send]
After a Google search to figure out why the POST shows up as a GET in their log, I found this Adobe technote (http://kb2.adobe.com/cps/159/tn_15908.html). Here's what it says:
When loadVariables or getURL actions are
used to send data to Java servlets it
can appear that the data is being sent
using a GET request, when the POST
method was specified in the Flash
movie.
This happens because Flash sends the
data in a GET/POST hybrid format. If
the data were being sent using a GET
request, the variables would appear in
a query string appended to the end of
the URL. Flash uses a GET server
request, but the Name/Value pairs
containing the variables are sent in a
second transmission using POST.
Although this causes the servlet to
trigger the doGet() method, the
variables are still available in the
server request.
I don't really understand that. What is a "GET/POST hybrid format"?
Why does the method Flash uses (POST or GET) depend on whether the data is sent to a Java servlet or elsewhere (e.g., a PHP page?)
Can anyone make sense of this? Many thanks in advance!
Cheers,
Matt

Have you try doing something like that :
var sendVar=new LoadVars();
var xml=new XML("<r>test</r>");
sendVar.xml=xml;
sendVar.svc="setPayCheckInfo";
var receiveXML=new XML();
function onLoad(success) {
if (success) {
trace("receive:"+receiveXML);
} else {
trace('error');
}
}
receiveXML.onLoad=onLoad;
sendVar.sendAndLoad("http://mywebserver", receiveXML, "POST");

The hybrid format is just a term Macromedia invented to paint over its misuse of HTTP.
HTTP is very vague on what you can do with GET and POST. But the convention is that no message body is used in GET. Adobe violates this convention by sending parameters in the message body.
Flash sends the same request regardless of the server. You have problem in Servlet because most implementation (like Tomcat) ignores message body for GET. PHP doesn't care the verb and it processes the message body for GET too.