=JSON Array to Arraylist (Android)

谁能告诉我我的代码出了什么问题？我一直在尝试从返回 json 数组的 PHP 文件中检索数据。我的安卓应用程序崩溃了。

我的 PHP 代码

<?php
/*
Our "config.inc.php" file connects to database every time we include 
or require
it within a php script.  Since we want this script to add a new user
to  our db,
we will be talking with our database, and therefore,
let's require the connection to happen:
*/
require("config.inc.php");

$query = "select * from view_examquestions where examid=5";
try{
    $stmt = $db->prepare($query);
    $result = $stmt->execute();
}catch (PDOException $e){
    $response["success"] = 0;
    $response["message"] = "Database Error!";
    echo $e;
    die(json_encode($response));
}
$rows = $stmt->fetchAll();

$num = rand(0, 4);
if ($rows) {
$response["success"] = 1;
$response["message"] = "Post Available!";
$response["posts"]   = array();
        $counter = 0;
foreach ($rows as $row) {
    $post             = array();
    $post["questionid"]  = $row["questionid"];
    $post["description"] = $row["description"];
    $post["questiontype"]    = $row["questiontype"];
    $post["weight"]  = $row["weight"];
    $post["examid"]  = $row["examid"];
    array_push($response["posts"], $post);
}
// echoing JSON response
echo json_encode($response);

} else {
      $response["success"] = 0;
      $response["message"] = "There are no questions!!";
      die(json_encode($response));
 }
?>

这是我的 JSONParser 类：

public class JSONParser {
static InputStream is = null;
static JSONObject jObj = null;
static String json = "";
// constructor
public JSONParser() {
}

public JSONObject getJSONFromUrl(final String url) {
    // Making HTTP request
    try {
        // Construct the client and the HTTP request.
        DefaultHttpClient httpClient = new DefaultHttpClient();
        HttpPost httpPost = new HttpPost(url);
        // Execute the POST request and store the response locally.
        HttpResponse httpResponse = httpClient.execute(httpPost);
        // Extract data from the response.
        HttpEntity httpEntity = httpResponse.getEntity();
        // Open an inputStream with the data content.
        is = httpEntity.getContent();
    } catch (UnsupportedEncodingException e) {
        e.printStackTrace();
    } catch (ClientProtocolException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
    try {
        // Create a BufferedReader to parse through the inputStream.
        BufferedReader reader = new BufferedReader(new InputStreamReader(
                is, "iso-8859-1"), 8);
        // Declare a string builder to help with the parsing.
        StringBuilder sb = new StringBuilder();
        // Declare a string to store the JSON object data in string form.
        String line = null;
        // Build the string until null.
        while ((line = reader.readLine()) != null) {
            sb.append(line + "'n");
        }
        // Close the input stream.
        is.close();
        // Convert the string builder data to an actual string.
        json = sb.toString();
    } catch (Exception e) {
        Log.e("Buffer Error", "Error converting result " + e.toString());
    }
    // Try to parse the string to a JSON object
    try {
        jObj = new JSONObject(json);
    } catch (JSONException e) {
        Log.e("JSON Parser", "Error parsing data " + e.toString());
    }
    // Return the JSON Object.
    return jObj;
}

// function get json from url
// by making HTTP POST or GET mehtod
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
            // defaultHttpClient
            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 {
        jObj = new JSONObject(json);
    } catch (JSONException e) {
        Log.e("JSON Parser", "Error parsing data " + e.toString());
    }
    // return JSON String
    return jObj;
}
}`

这是我检索数据的活动代码：

public class ChooseOption extends Activity {

private Button mTakeExam;
private Button mPrevScore;
private  TextView status;
private static final String READ_QUESTIONS_URL = "http://192.168.0.20:80/EMA/webservice/questions.php";
// JSON IDS:
private static final String TAG_QUESTIONID = "questionid";
private static final String TAG_DESCRIPTION = "description";
private static final String TAG_QUESTIONTYPE = "questiontype";
private static final String TAG_WEIGHT = "weight";
private static final String TAG_EXAMID = "examid";
private static final String TAG_POSTS = "posts";
private static final String TAG_SUCCESS= "success";
//private String done = "Questions loaded!";
private ProgressDialog pDialog;
private static JSONArray mQuestions = null;
public static ArrayList<Question> mQuestionList;
@Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    setContentView(R.layout.chooseoption);
    mTakeExam = (Button) findViewById(R.id.bTakeExam);
    mPrevScore = (Button) findViewById(R.id.bPrevScore);
    status = (TextView) findViewById(R.id.tSample);
    mTakeExam.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View arg0) {
            // TODO Auto-generated method stub
            new LoadQuestions().execute();
        }
    });
}

private class LoadQuestions extends AsyncTask<String, String, String>
{
    @Override
    protected void onPreExecute() {
        // TODO Auto-generated method stub
        super.onPreExecute();
        pDialog = new ProgressDialog(ChooseOption.this);
        pDialog.setMessage("Retrieving Questions");
        pDialog.setIndeterminate(false);
        pDialog.setCancelable(true);
        pDialog.show();
    }
    @Override
    protected String doInBackground(String... arg0) {
        // TODO Auto-generated method stub
        JSONParser jParser = new JSONParser();
        //JSONObject json = jParser.getJSONFromUrl(READ_QUESTIONS_URL);
        try {
        JSONObject json = jParser.getJSONFromUrl(READ_QUESTIONS_URL);
        mQuestions = json.getJSONArray(TAG_POSTS); 
        int success = json.getInt(TAG_SUCCESS); 
        if (success == 1) { 
        status.setText("Retrieved! :)");
        }
        for (int i = 0; i < mQuestions.length(); i++) {
            JSONObject c = mQuestions.getJSONObject(i);
            // gets the content of each tag     
            String questionid = c.getString(TAG_QUESTIONID);
            String description = c.getString(TAG_DESCRIPTION);
            String questiontype = c.getString(TAG_QUESTIONTYPE);
            String weight = c.getString(TAG_WEIGHT);
            String examid = c.getString(TAG_EXAMID);
            Question ques = new Question();
            ques.setDescription(description);
            ques.setExamid(Integer.parseInt(examid));
            ques.setQuestionid(Integer.parseInt(questionid));
            ques.setQuestiontype(questiontype);
            ques.setWeight(Integer.parseInt(weight));
            mQuestionList.add(ques); 
        } 
        } catch (JSONException e) {
            status.setText("No questions!");
            e.printStackTrace();
        }

        return null; 
    }

    @Override
    protected void onPostExecute(String result) {
        // TODO Auto-generated method stub
        pDialog.dismiss();
    }
}
}

这是我的问题类：

public class Question {
private int questionid;
private String description;
private String questiontype;
private int weight;
private int examid;
public Question()
{
    this.questionid = 0;
    this.description = "";
    this.questiontype = "";
    this.weight = 0;
    this.examid = 0;
}
public int getQuestionid() {
    return questionid;
}
public void setQuestionid(int questionid) {
    this.questionid = questionid;
}
public String getDescription() {
    return description;
}
public void setDescription(String description) {
    this.description = description;
}
public String getQuestiontype() {
    return questiontype;
}
public void setQuestiontype(String questiontype) {
    this.questiontype = questiontype;
}
public int getWeight() {
    return weight;
}
public void setWeight(int weight) {
    this.weight = weight;
}
public int getExamid() {
    return examid;
}
public void setExamid(int examid) {
    this.examid = examid;
}

}

当我尝试运行我的问题.php文件时，我得到以下数据：

{"成功"：1，"消息"："帖子可用！"，"帖子"：[{"questionid"："1"，"description"："谁是生物学之父？"，"questiontype"："识别"，"权重"："2"，"examid"："5"}，{"questionid"："2"，"description"："是你吗？"，"questiontype"："TF"，"weight"："1"，"examid"："5"}，{"questionid"："3"，"description"："谁

是iKon的领导者？"，"questiontype"："MC"，"weight"："2"，"examid"："5"}，{"questionid"："7"，"description"："字母表的第二个字母是什么？"问题类型"："标识"，"权重"："2"，"examid"："5"}，{"questionid"："8"，"description"："这个应用程序的名称是什么？"，"questiontype"："标识"，"权重"："3"，"examid"："5"}， {"questionid"："9"，"description"："你吃午饭了吗？"，"questiontype"："TF"，"weight"："2"，"examid"："5"}]}