试图获得表行计数值，但得到错误转换结果java.lang.NullPointerException: lock == n

我是新的，所以我需要帮助我目前的问题，我试图获得表行计数值，但"错误解析数据org.json.JSONException:类型java.lang.String的值结果不能转换为JSONObject"出现

这是我的rowcount。php:

<?php
$mysqli = new mysqli("localhost", "root", "", "smkkimmanuel2");
/* check connection */
if (mysqli_connect_errno()) {
    printf("Connect failed: %s'n", mysqli_connect_error());
    exit();
}
if ($result = $mysqli->query("SELECT * FROM pendaftaran")) {
    /* determine number of rows result set */
    $row_cnt = $result->num_rows;
	printf("Result set has %d rows.'n", $row_cnt);
	$response["rowcount"] = $row_cnt;
	die(json_encode($response));
}
?>

和row_count_test类:

package id.wanda.smkkkristenimmanuelii;
import org.json.JSONException;
import org.json.JSONObject;
import android.app.Activity;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;
public class Row_count_test extends Activity {
	private TextView testRowCount;
	
	// flag for Internet connection status
    Boolean isInternetPresent = false;
     
    // Connection detector class
    ConnectionDetector cd;
	// JSON parser class
	JSONParser jsonParser = new JSONParser();
	private static final String LOGIN_URL = "http://192.168.1.110/smkkimmanuel2/rowcount.php";
	// JSON element ids from repsonse of php script:
	private static final String TAG_ROWCOUNT = "rowcount";
	public static String row;
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		// TODO Auto-generated method stub
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_row_count_test);
		
		testRowCount = (TextView) findViewById(R.id.test);
		new RowCount().execute();
	}
	public void rowCount(View v) {
		
		
	}
	class RowCount extends AsyncTask<String, String, String> {
		
		@Override
		protected String doInBackground(String... args) {
			String getRow;
			// getting product details by making HTTP request
			JSONObject json = jsonParser.makeHttpRequestRowCount(LOGIN_URL);
			try {
					getRow = json.getString(TAG_ROWCOUNT);
					row = getRow;
					
				
			} catch (JSONException e) {
				e.printStackTrace();
			}catch (NullPointerException e) {
				   e.printStackTrace();
			}
			return row;
		}
		
		@Override
		protected void onPostExecute(String row) {
			// TODO Auto-generated method stub
			testRowCount.setText(row);
		}
	}
	
}

这是我的JSONObject @PareshMayani先生:

public JSONObject makeHttpRequestRowCount(String url, String method) {
 
        // Making HTTP request
        try {
                DefaultHttpClient httpClient = new DefaultHttpClient();
                HttpPost httpPost = new HttpPost(url);
 
                HttpResponse httpResponse = httpClient.execute(httpPost);
                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());
        }
        Log.d("JSON Parser", json);
        // 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;
 
    }

编辑:似乎问题发生在PHP文件中，它返回空值。我需要PHP文件

的帮助下面是新的logcat错误:

05-26 11:28:46.530: E/Buffer Error(15945): Error converting result java.lang.NullPointerException: lock == null
05-26 11:28:46.530: E/JSON Parser(15945): Error parsing data org.json.JSONException: End of input at character 0 of 

下面是新的rowcount.php文件:

<?php
$mysqli = new mysqli("localhost", "root", "", "smkkimmanuel2");
/* check connection */
if (mysqli_connect_errno()) {
    printf("Connect failed: %s'n", mysqli_connect_error());
    exit();
}
if ($result = $mysqli->query("SELECT * FROM pendaftaran")) {
    /* determine number of rows result set */
    $row_cnt = $result->num_rows;
	
	$response["rowcount"] = $row_cnt;
	echo json_encode($response);exit;
}
?>

$row_cnt = $result->num_rows;
// remove this line
//printf("Result set has %d rows.'n", $row_cnt);
$response["rowcount"] = $row_cnt;
//replace this line
//die(json_encode($response));
echo json_encode($response);exit;

testRowCount.setText(row);

<?php
	$username = "root";
	$password = "";
	$host = "localhost";
	$dbname = "smkkimmanuel2";
    $options = array(PDO::MYSQL_ATTR_INIT_COMMAND => 'SET NAMES utf8'); 
    try 
    { 
        $db = new PDO("mysql:host={$host};dbname={$dbname};charset=utf8", $username, $password, $options); 
    } 
    catch(PDOException $ex) 
    { 
        die("Failed to connect to the database: " . $ex->getMessage()); 
    } 
     
    $db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);      
    $db->setAttribute(PDO::ATTR_DEFAULT_FETCH_MODE, PDO::FETCH_ASSOC); 
     
    if(function_exists('get_magic_quotes_gpc') && get_magic_quotes_gpc()) 
    { 
        function undo_magic_quotes_gpc(&$array) 
        { 
            foreach($array as &$value) 
            { 
                if(is_array($value)) 
                { 
                    undo_magic_quotes_gpc($value); 
                } 
                else 
                { 
                    $value = stripslashes($value); 
                } 
            } 
        } 
     
        undo_magic_quotes_gpc($_POST); 
        undo_magic_quotes_gpc($_GET); 
        undo_magic_quotes_gpc($_COOKIE); 
    } 
     
    header('Content-Type: text/html; charset=utf-8'); 
     
    session_start(); 
?>

<?php
//load and connect to MySQL database stuff
require("config.php");
    //gets user's info based off of a username.
    $query = "SELECT * FROM pendaftaran_calon_siswa";
    
    
    try {
        $stmt   = $db->prepare($query);
        $stmt->execute();
    }
    catch (PDOException $ex) {
        // For testing, you could use a die and message. 
        //die("Failed to run query: " . $ex->getMessage());
        
        //or just use this use this one to product JSON data:
        $response["success"] = 0;
        $response["message"] = "Database Error1. Please Try Again!";
        die(json_encode($response));
        
    }
    
    //fetching all the rows from the query
	$row = $stmt->fetchAll();
	$rows = count($row);
    
	$response["rowcount"] = $rows;
	echo json_encode($response);
    
?>