如何用java发送JSON格式的请求到Keystone 给用户加admin角色？

我想用java发送json格式的命令到keystone给指定的用户加admin角色，我找到了一个rackspace发布的keystone API extension,其中有"add global role to user" API, 网址是：http://docs.rackspace.com/openstack-extensions/auth/OS-KSADM-admin-devguide/content/PUT_addUserRole_v2.0_users__userId__roles_OS-KSADM__roleId__Admin_API_Service_Developer_Operations-d1e1357.html我试着按照API中的URI格式发送请求，可是得不到结果，我的代码：
其中c53612ae37ec4721a7a72863a1c48726为User_id, 3a6089fd5802419ea97d14a4909b9853为admin_idprivate static void addRole(){
     try {
            //创建连接
   URL url = new URL(key_admin_url + "/users/" + "c53612ae37ec4721a7a72863a1c48726" + "/roles/OS-KSADM/" + "3a6089fd5802419ea97d14a4909b9853");
            HttpURLConnection connection = (HttpURLConnection) url
                    .openConnection();
            connection.setDoOutput(true);
            connection.setDoInput(true);
            connection.setRequestMethod("PUT");
            connection.setUseCaches(false);
            connection.setInstanceFollowRedirects(true);
            connection.setRequestProperty("Content-Type",
                    "application/json");
            connection.setRequestProperty("X-Auth-Token",
                    "012345SECRET99TOKEN012345");
            connection.connect();           //POST 请求 
            DataOutputStream out = new DataOutputStream(
                    connection.getOutputStream());
            out.writeBytes("");
            out.flush();
            out.close();            //读取响应
            BufferedReader reader = new BufferedReader(new InputStreamReader(
                    connection.getInputStream()));
            String lines;
            StringBuffer sb = new StringBuffer("");
            while ((lines = reader.readLine()) != null) {
                lines = new String(lines.getBytes(), "utf-8");
                sb.append(lines);
            }
            System.out.println(sb);
            reader.close();
            // 断开连接
            connection.disconnect();
            
        } catch (MalformedURLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (UnsupportedEncodingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
请问有人这样连接过么？ 正确的发送方式应该是怎样的呢？谢谢jsonjavaapirackspacekeystone