Enviando arquivo via post

public static void sendFileXML(String xml) throws IOEXception{
    String query = xml;
          String charEncoding = "iso-8859-1";

    String location = "URL";

    HttpURLConnection conn = (HttpURLConnection) new URL(location).openConnection();
          conn.setDoOutput(true);
          conn.setDoInput(true);
          conn.setRequestMethod("POST");
          conn.setRequestProperty("Content-type", "text/xml");
          conn.setRequestProperty("Content-Length", Integer.toString(query.length()));
          
          conn.connect();
          
          conn.getOutputStream().write(query.getBytes(charEncoding));
          
          
          if (conn.getResponseCode() != 200 )
             System.out.println("Pagina indisponivel");
          else
          {
              InputStream postis = conn.getInputStream();
              StringBuffer retorno = new StringBuffer();
              int c = postis.read();
              while(c != -1) {
              retorno.append((char)c);
              c = postis.read(); 
              }
              System.out.println(retorno);
          }

            }