为什么JSON返回null？

Question

I 'm making an application that handles registration.I use PHP MYSQL.When i register ,the details entered are correctly inserted into the table but when echoed response it returns NULL with the message.

here is the picture

When in application this NULL is what i get as json feed thus i can't proceed further.

what i want is that the message should be either success or failure.I don't know whats wong with the code.Here is my PHP code:

<?php
include_once './DbConnect.php';
function createNewPrediction() {

     $response = array();
    $Name = $_POST["Name"];
    $College =  $_POST["College"];
    $Mobile =  ($_POST["Mobile_no_"]);
    var_dump( $Mobile);

    $Email =  $_POST["Email"];
            $db = new DbConnect();

   // mysql query
   mysql_query('SET CHARACTER SET utf8');
    $query = "INSERT INTO Register(Name,College,Mobile,Email)     VALUES('{$Name}','{$College}','{$Mobile}','{$Email}')";
    $result = mysql_query($query) or die(mysql_error());
    if ($result) {
        $response["error"] = false;
        $response["message"] = "Registered Successfully!!";
    } else {
        $response["error"] = true;
        $response["message"] = "Registration unsuccessfull!!";
    }
   // echo json response
   echo phpversion();
   echo json_last_error_msg();

echo json_encode($response);
}
createNewPrediction();
?>

As you can see i have tried 'json_last_error_msg()' it gives me no error.I don't understand where lies my fault.

Hope these materials are enough for the assessment of the question.Please help me out?

EDIT here is my java code making the calls and receiving the JSON. Let me elaborate the problem.In the below code 'line' that i'm using to pass the response to json is null.

Here is what i have tried in console:

1. I have tried 'reader.toString()', gave me nothing

2.I have tried 'is.toString()',strangely gave me message 'success' in console.

So problem seems to be in this code.I 'm very sorry that i said that the problem was with my php code.I 'ma beginner so please kindly understand me.Please help.

JSONparser

package com.defcomdevs.invento16;
import android.util.Log;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.util.List;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.client.utils.URLEncodedUtils;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONException;
import org.json.JSONObject;

 /**
 * Created by midhun on 18/11/15.
*/
public class JSONParser {

static  InputStream is= null;  //input stream object to hold incoming data
static  JSONObject obj=null;
static String json="";

//constructor
public JSONParser(){

}


//functionn to get json from URL
//by making HTTP POST or GET methods
public JSONObject makeHTTPRequest(String url, String method,List<NameValuePair> params){

    //making HTTP request
    try{

        //check for request method
        if (method== "POST"){

            //request method is post
            //call default http client
            DefaultHttpClient httpClient = new DefaultHttpClient();
            HttpPost httpPost = new HttpPost(url);
            httpPost.setEntity(new UrlEncodedFormEntity(params));

            HttpResponse httpResponse = httpClient.execute(httpPost);
            HttpEntity httpEntity = httpResponse.getEntity();
            is= httpEntity.getContent();
        }else if(method == "GET"){
            // request method is GET
            DefaultHttpClient httpClient = new DefaultHttpClient();
            String paramString = URLEncodedUtils.format(params, "utf-8");
            url += "?" + paramString;
            HttpGet httpGet = new HttpGet(url);

            HttpResponse httpResponse = httpClient.execute(httpGet);
            HttpEntity httpEntity = httpResponse.getEntity();
            is = httpEntity.getContent();
        }
    }catch (UnsupportedEncodingException e){
        e.printStackTrace();
    }catch (ClientProtocolException e){
        e.printStackTrace();
    }
    catch (IOException e){
        e.printStackTrace();
    }
    try {
        BufferedReader reader= new BufferedReader(new InputStreamReader(is,"iso-8859-1"),8);
        StringBuilder sb = new StringBuilder();
        String line= null;
        while((line = reader.readLine())!=null){
            sb.append(line +"\n");
        }
        is.close();
        json = sb.toString();

    }catch (Exception e){
        Log.e("Buffer Error", "Error converting result " + e.toString());
    }

    //try parse the string to A JSON object

    try{
        obj=new JSONObject(json);
    }catch (JSONException e){
        e.printStackTrace();
    }
    return obj;
}

public static  String returnJSON(){
    return json;
}
}

Answer 1

you get the out put the three echo's

 echo phpversion();
    echo json_last_error_msg();

    echo json_encode($response);

and var_dump( $Mobile);

Answer 2

You have no problem here,

var_dump -> NULL
echo phpversion(); -> 5.6.4 ...
echo json_last_error_msg();->No error
echo json_encode($response);->{"error":false,"message":"Registered Successfully!!"}

Remove everything but json_encode and you actually get exactly what you want