public class SelectbyID extends AsyncTask<String,Void,String> {
String link = "http://survivinginporto.atwebpages.com/SelectbyID.php";
    int id;
String JSON_STRING;

@Override
protected String doInBackground(String... params) {
String username = params[0];

try {

    URL url = new URL(link);
    HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
    httpURLConnection.setRequestMethod("POST");
    httpURLConnection.setDoOutput(true);


    OutputStream OS = httpURLConnection.getOutputStream();
    BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(OS, "UTF-8"));
    String data = URLEncoder.encode("username", "UTF-8") + "=" + URLEncoder.encode(username, "UTF-8");



    bufferedWriter.write(data);
    bufferedWriter.flush();
    bufferedWriter.close();
    OS.close();


    InputStream inputStream = httpURLConnection.getInputStream();
    BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
    StringBuilder stringBuilder = new StringBuilder();
    while ((JSON_STRING = bufferedReader.readLine()) != null) {
        stringBuilder.append(JSON_STRING + "n");
    }

    bufferedReader.close();
    inputStream.close();
    httpURLConnection.disconnect();
    return stringBuilder.toString().trim();
  //  InputStream IS = httpURLConnection.getInputStream();
  //  IS.close();

   // httpURLConnection.disconnect();


} catch (MalformedURLException e) {
    e.printStackTrace();
} catch (UnsupportedEncodingException e) {
    e.printStackTrace();
} catch (ProtocolException e) {
    e.printStackTrace();
} catch (IOException e) {
    e.printStackTrace();
}
return null;
  }


@Override
protected void onPreExecute() {
   link = "http://survivinginporto.atwebpages.com/SelectbyID.php";
    System.out.println("2");
}

@Override
protected void onProgressUpdate(Void... values) {

    System.out.println("progress update");
    super.onProgressUpdate(values);
}


@Override
protected void onPostExecute(String id2)
{
    System.out.println("COMEÇA O POST");
   // int id = 0;


    System.out.println("3");
    try
    {
        JSONObject jsonObject2 = new JSONObject(id2);
        JSONArray jsonArray2 = jsonObject2.getJSONArray("id2");


        for(int i=0;i<jsonArray2.length();i++)
        {

            JSONObject JO2 = jsonArray2.getJSONObject(i);
            System.out.println("run for"); //DOENST SHOW !

            //get an output on the screen




            id=JO2.getInt("id");
            System.out.println("SELECTBYID:::::::::::::::::::::::::::::::::::NESTE MOMENTO O ID = " + id);



        }



        System.out.println("O ID DO USER É: " + id);
   // RetornaID(id);
        System.out.println("4");
        turnidtovalue(id);

    } catch (JSONException e) {
        e.printStackTrace();
    }


}

<?php
$host = "";
$user = "";
$pass = "";
$db = "";


$con = mysqli_connect($host,$user,$pass,$db);

if(!$con)
    {
        //die("Error ".mysqli_connect_error());
     }
     else
     {

        //echo "<h3>connection success</h3>";

     }

     //Recebendo a informação
$username = $_POST["username"];


     $sql = "select id from androidotp where username='$username'";

     $id2 = mysqli_query($con,$sql);

     $response = array();


      while($row=mysqli_fetch_array($id2))
       {

        array_push($response,array('id'=>$row[0]));


         }

         echo json_encode(array('id2'=>$response));

           mysqli_close($con);?>