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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/

Separate GET parameters from POST in embedded Jetty server

I need to know wheather the parameter is GET or POST but in handle method request.getParameter(name) gives me all parameters. Is it possible to do something like request.getGETParameter(name) and request.getPOSTParameter(name) or do I have to parse raw data myself?

There is no such thing as GET parameters and POST parameters. GET and POST are methods of HTTP request.
You can find out which method your request is by calling
public String getMethod();
on your request.
You might also want to take a look on the description of HTTP protocol http://en.wikipedia.org/wiki/Hypertext_Transfer_Protocol
The difference between parameters being sent in GET in and POST method is that in GET request parameters are sent in query string, and in POST request these are sent in request body.

why we need to use get method inside a java file #RequestMapping(method = RequestMethod.GET)

In generally while sending form data from the ui pages we are using method="GET" or method="POST" in the form tag then what is the use of these methods in the server side programs. I am using these methods in spring while calling the methods in the controller #RequestMapping(method = RequestMethod.GET)
Can anyone explain what is the real use of get or post methods in server side code

Loosely speaking, if the purpose of your method is to retrieve data from the server use GET. e.g. getting information to display on the client.
If you are sending data to the server use POST. e.g. sending information to the server to be saved on a database somewhere.
There is a limit to the size of data you can send to the server with a GET request.

The server side GET or POST is used to specify what the server expects to receive in order to accept the request. The client side GET or POST is used to specify what will be sent to the server. These two must match. You cannot send a GET request when server expects a POST and vice-versa.
When you are building a server application, it is important to know the appropriate request type to use, which by itself is a whole big different topic which you should research if it is you the one that builds the server side part.

How do I send a list to the jsp that requested it?

Let us suppose there is a jsp that needs to display the list of files shared shared by a particular IP. Client opens that jsp on his local server and the request is sent to a remote server to fetch the list.
Servlet on the server processes the request and fetches the list of files shared by that IP. Now how do the servlet send that list to the jsp page that requested it ?
JSP :
connection.openConnection(); // Connection sends IP as the query parameter to the
// remote servlet
Servlet :
doGet(..parameters..) {
list = getList(forThatIP);
// NOW HOW DO I SEND THIS LIST ?
}
One method that I thought was to send the whole data as a query string to a servlet on the client side(running a server such as tomcat) and then stash that list onto some file.Later jsp can parse the file and display the data. But that doesn't seem to be a good option.
Note: JSP is invoked when a servlet forwards after successfully sending the IP to remote servlet

You can use request.setAttribute() in the Servlet. Then you can use a JSP tag to retrieve the value in JSP. Investigate a bit on that.
EDIT :
In the Servlet doGet method, you can set the an attribute, say listOfFiles as:
resquest.setAttribute("listOfFiles",list);
Then in the JSP you can retirieve it using the EL expression:
${listOfFiles}
which is an inbuilt feature of JSP.
Alternatively, you can access it using
<% request.getAttribute("listOfFiles")%>
but it is bad to embed Java scriptlets inside JSPs.

If you're passing complex data (lists etc.) over a connection, you can look into using JSON or XML. Your JSP code should be able to parse either easily with the right library.

Actually it depends on how the jsp is invoked.
Do you perform a post onto it ? Does the servlet perform a forward ? Or is a sendRedirect() ?
According to this there are many ways to send data to your jsp. One is using request attributes or better, using request scoped beans. One other can be posting some sort of rappresentation of your list as a post parameter (be it json, xml or some custom format of yours).
Another thing to consider is, what are you using ? JSF ? Some Spring library ? According to that there may be other better (or worse) ways to send datas.
If working with simple JSP/Servlet on a small project I'd personally go with the request.setAttribute() way, indeed this will force me to invoke the jsp via something like
request.setAttribute("myList", yourListObject);
request.getRequestDispatcher("yourjsp.jsp").forward(request, response);
then in the jsp you can:
<% Object myListObj = pageContext.getRequest().getAttribute("myList"); %>

When you call a servlet from code, the best way is to use an HttpServlet and mimic the browser behavior.
Passing the data in the URL is a GET request. Useful only with relatively small chunks of data, but the semantics look like you want ("get a bit of data"). Something like http://myremoteserver.com/myServlet?ip=.... You will need a proper encoding of the parameters (the Java API can handle that).
Passing the data by writting into the stream will be a POST request. It has no limit in the data passed to the server, but the semantics is different ("change something in the system"). You could pass your data as a parameter inside the contents written, I am not really sure how to decode that. Another alternative is using a Servlet (no HttpServlet) and just treat the raw data.
In both cases the response will be returned in the connection output stream. You can use whatever format you like (an standard one like JSON will probably be best, even that defining your own XML). In this case, a viable alternative would be filenames separated by a 'safe' character (like \n or |). Quick, but it will be less flexible in the future.
I would go for a GET request and JSON encoding.

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.