从android到PHP的HTTP post调用？

Question

I am new working with Android Studio. Here in the below code i am trying to send data from java to the backend server (in PHP). The call is being made but NULL is returned from the server side which shouldn't happen. So I think input sent from the java side is not interpreted properly at the PHP side i guess. Could you tell what is wrong with the code (and PHP code is perfectly all right and it should not return NULL).

          HttpURLConnection httpURLConnection = null;
          JSONObject  Student_det = stu_det.getJSONObject(i);
          String stu_GUID = Student_det.getString("StuGUID");
          String visit_GUID = Student_det.getString("VisitGUID");

            String value = "Rec="+(tableRow+1)+"&SchGUID="+schoolGUID.trim()+"&StuGUID="+stu_GUID.trim()+"&VisitGUID="+visit_GUID.trim()+"&role="+role;
            URL url = new URL("http://52.66.25.82/api/download_student.php");
            String enc_val = URLEncoder.encode(value,"UTF-8");

            httpURLConnection = (HttpURLConnection) url.openConnection();
            httpURLConnection.setDoOutput(true);
            httpURLConnection.setDoInput(true);

            httpURLConnection.setRequestMethod("POST");



            OutputStreamWriter wr = new OutputStreamWriter(httpURLConnection.getOutputStream());
            wr.write( enc_val );
            wr.flush();

            InputStream responseStream = new BufferedInputStream(httpURLConnection.getInputStream());

            BufferedReader responseStreamReader =
                    new BufferedReader(new InputStreamReader(responseStream));


            // Read Server Response
         String output = responseStreamReader.readLine();

Answer 1

As you said new to android, start with best possible way

Try to implement with volley library or RetroFit lib,its easy and simple

volley example

OR

RetroFit example