Java client throwing Unsupported Media Type Exception

I am developing an application that uses restful api. A java client sending a request to a standalone server is throwing Unsupported Media Type exception. The client code is as follows

StringBuilder xml = new StringBuilder();
                xml.append("<?xml version=\"1.0\" encoding=\"${encoding}\"?>").append("\n");
                xml.append("<root>").append("\n");
                xml.append("<user>").append("\n");
                xml.append("<username>"+username+"</username>");
                xml.append("\n");
                xml.append("<password>"+pass+"</password");
                xml.append("\n");
          开发者_开发知识库      xml.append("</user>");
                xml.append("</root>");
                Representation representation = new StringRepresentation(xml.toString());
                new ClientResource("http://localhost:7777/Auth").post(representation);

Server code is as follows

new Server(Protocol.HTTP,7777,TestServer.class).start();
String username = (String) getRequest().getAttributes().get("username");
        String password=(String) getRequest().getAttributes().get("password");
        StringRepresentation representation = null; 

You are not passing the content-type header; I strongly recommend using an API like Apache Common HttpClient to produce such requests (and maybe read the contents from a file).

@Riccardo is correct, the Restlet Resource on the server is checking the Content-Type header of the client's request to make sure the entity you're POSTing to the server has a type it can support. Here's a Restlet 1.1 example. You'll notice that that Resource is set up to expect XML:

// Declare the kind of representations supported by this resource.  
getVariants().add(new Variant(MediaType.TEXT_XML));  

So maybe your server side doesn't declare the representations it can handle, or it does and Restlet's automatic media type negotiation is detecting that your request doesn't have Content-Type: text/xml (or application/xml) set.

So as @Riccardo suggests, use Apache HttpClient and call HttpRequest.setHeader("Content-Type", "text/xml"), or use Restlet's client library API to do this (it adds another abstraction layer on top of an HTTP client connector like Apache HttpClient).