java: Spring @RequestBody and @ResponseBody not working with java.net

Here is my java.net client code

    URL server = new URL(serverUrl);
    URLConnection connection = server.openConnection();

    /* DoOutput flag is set to true to inform URL connection that we are
     * sending data out. The default behavior is false. This will change
     * the request from GET to a POST.
     */
    connection.setDoOutput (true);

    /* Setting the UseCaches to false allows the application "tunnel
     * through" and ignore the caches.
     */
    connection.setUseCaches (false);

    connection.setRequestProperty ( "Content-Type", "application/octet-stream" );

    ObjectOutputStream sendData = new ObjectOutputStream(connection.getOutputStream());
    sendData.writeObject(packet);
    sendData.flush();
    sendData.close();

    ObjectInputStream recieveData = new ObjectInputStream(connection.getInputStream());
    response =  (Serializable) recieveData.readObject();

    System.out.println(response);

    recieveData.close();

And this is my server code with spring to receive the request and send back response

@ResponseBody
@RequestMapping(value="/upload", method=RequestMethod.POST)
public Serializable fileUploadHandler(@RequestBody FilePacket packet, HttpServletRequest request, HttpSession session, HttpServletResponse response){

    // handle request

    return "response";      
}

While running the code with above configuration, upon sending the request to server, I get Http error 415

java.io.IOException: Server returned HTTP response code: 415 for URL:

I removed @RequestBody and replaced it with

FilePacket packet = (FilePacket) new ObjectInputStream(request.getInputStream()).readObject();

and the request part was good. But then after a request I got the 406

java.io.IOException: Server returned HTTP response code: 415 for URL:

and so I replaced @ResponseBody with

new ObjectOutputStream(response.getOutputStream()).writeObject("response");

and then everything was good.

I've used these annotations with ajax and they work like charm but with java.net , I'm getting unsupported media type (415) and not acceptable (406). Is spring not able to read the request and send proper response or I'm missing something here? Is there a way to make it work?

Note: The class FilePacket is Serializable, one of whose fields is of type byte[] which holds the file data.