在android中检索JSON数据

我正试图从我的android应用程序中的服务器检索JSON数据。JSON文件包括问题与4个选择。我试图单独检索问题和4个选择，并设置为列表视图在安卓显示喜欢选择题。Android通过响应，但我无法获得个人数据。下面是我的代码。

file.json

 {"multiple":[{
"question": "In which course are you inrolled in?",
"choice 1":"BIM",
"choice 2":"BBA",
"choice 3":"BIT",
"choice 4":"BSCCSIT"
},
{
"question": "What comes after n?",
"choice 1":"s",
"choice 2":"t",
"choice 3":"o",
"choice 4":"p"
}
]
}

sending.php

<?php
    header('Content-type:application/json');
$data =file_get_contents('/var/www/html/file.json');
$row =json_encode($data);
echo ($row);
?>

MainActivity.java

package com.multiple;
import android.app.*;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.widget.*;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.util.EntityUtils;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.IOException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;

public class MainActivity extends Activity
{
    private ListView listview;
    List<HashMap<String,String>> collect= new ArrayList<HashMap<String, String>>();
    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        listview = (ListView) findViewById(R.id.list);
        populate p = new populate();
        p.execute();
    }
    public class populate extends AsyncTask<Void, Void, Void>
        {
            public Void doInBackground(Void... params)
            {
                    try
                    {
                        HttpClient client = new DefaultHttpClient();
                        HttpGet post = new HttpGet("http://192.168.10.120/sending.php");
                        HttpResponse res= client.execute(post);
                        HttpEntity entity = res.getEntity();
                        String response = EntityUtils.toString(entity);
                        Log.i("response",response);

                        JSONObject obj = new JSONObject(response);

                        JSONArray jsonArray = obj.optJSONArray("multiple");
                        for(int i=0; i < jsonArray.length(); i++)
                        {
                            JSONObject jsonObject = jsonArray.getJSONObject(i);
                            String id = jsonObject.optString("question").toString();
                            String name = jsonObject.optString("choice1").toString();
                            String salary =jsonObject.optString("choice2").toString();
                            String ssalary =jsonObject.optString("choice3").toString();
                            String sssalary =jsonObject.optString("choice4").toString();
                            Log.i("qq",id);
                            Log.i("asdfas",salary);
                            Log.i("asjdfha",name);
                            Log.i("asdfas",salary);
                        }
//                      String questions = obj.optString("question").toString();
//                      String choices=obj.optString("answerswers").toString();
                    }
                    catch(IOException ex){}
                    catch(JSONException ex){}
                return  null;
            }
            protected void onPostExecute(Void result)
            {
                super.onPostExecute(result);
            }
        }
        String[] str = new String[]{"first","second","third","fourth","fifth"};
        int[] val = new int[]{R.id.textView1,R.id.checkBox1,R.id.checkBox2,R.id.checkBox3,R.id.checkBox4};
}

如何单独检索JSON数据?/