在Android应用程序

Question

我正在尝试将post请求实现到我的android应用程序。但不幸的是，我得到状态代码500作为回应。这是我的代码

public class SendPostRequest extends AsyncTask<String, Void, String> {

        protected void onPreExecute(){}

        protected String doInBackground(String... arg0) {

            try {

                URL url = new URL("http://serveruri/auth/register"); // here is your URL path

                JSONObject postDataParams = new JSONObject();
                postDataParams.put("username", "abcdsdgvsdf");
                postDataParams.put("password", "abcmail");
                postDataParams.put("email", "abc@gmail.com");

                Log.e("params",postDataParams.toString());

                HttpURLConnection conn = (HttpURLConnection) url.openConnection();
                conn.setReadTimeout(15000 /* milliseconds */);
                conn.setConnectTimeout(15000 /* milliseconds */);
                conn.setRequestMethod("POST");
                conn.setRequestProperty("Accept", "application/json");
                conn.setRequestProperty("Content-Type", "application/json");
                conn.setDoInput(true);
                conn.setDoOutput(true);

                OutputStream os = conn.getOutputStream();
                BufferedWriter writer = new BufferedWriter(
                        new OutputStreamWriter(os, "UTF-8"));
                writer.write(getPostDataString(postDataParams));

                writer.flush();
                writer.close();
                os.close();

                int responseCode=conn.getResponseCode();
                Log.d("responsecode", String.valueOf(responseCode));

                if (responseCode == HttpsURLConnection.HTTP_OK) {

                    BufferedReader in=new BufferedReader(new
                            InputStreamReader(
                            conn.getInputStream()));

                    StringBuffer sb = new StringBuffer("");
                    String line="";

                    while((line = in.readLine()) != null) {

                        sb.append(line);
                        break;
                    }

                    in.close();
                    return sb.toString();

                }
                else {
                    return new String("false : "+responseCode);
                }
            }
            catch(Exception e){
                return new String("Exception: " + e.getMessage());
            }

        }

        @Override
        protected void onPostExecute(String result) {
            Toast.makeText(getApplicationContext(), result,
                    Toast.LENGTH_LONG).show();
        }
    }

我在邮递员身上测试过相同的uri，它正在工作。

这是什么问题？我该如何解决这个问题？