请问我用HttpURLConnection来post到http上去后，手机收到中文及中文后就空的了，请问是什么原因？

URL url = null;
        HttpURLConnection httpurlconnection = null;
PrintWriter out = response.getWriter();
        try {
String tel ="1375117989";
String content = "第一搜股网！";
            url = new URL("http://www.wwww.com/ww.php");
            httpurlconnection = (HttpURLConnection)url.openConnection();
            httpurlconnection.setDoOutput(true);
            httpurlconnection.setRequestMethod("POST");
httpurlconnection.setRequestProperty("Cache-Control", "private");
httpurlconnection.setRequestProperty("Accept-Charset", "gb2312");
httpurlconnection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded"); 
            String username = "<?xml version='1.0' encoding='UTF-8'?><SmsSubmitReq><from value='"+tel+"'/><to value='"+tel+"'/><feeType value='test'/><gid value='1'/><linkid value=''/><charset value='UTF-8'/><data>sanyou2312三忧14243</data></SmsSubmitReq>";
httpurlconnection.getOutputStream().write(username.getBytes());
            httpurlconnection.getOutputStream().flush();
            httpurlconnection.getOutputStream().close();
            int code = httpurlconnection.getResponseCode();//最后手机收到只有sanyou2312，请问如何解决？
我用xmlhttp方式post就不会有这种情况。