Returned JSONObject is always null

Question

I'm developing an android app which sends username and password to MySQL database and receives response ("success" or "error") in the login activity. But the returning JSONObject is null. Below are the codes

userauth.php

<?php
    //Connecting to mysql db
    include("db.php");

    //Check for POST request
    //if(isset($_POST['tag']) && $_POST['tag'] !=''){
        //Get tag
    //  $tag = $_POST['tag'];
    //}
    //Getting username and password from android via JSON
    $username = $_POST['username'];
    $password = $_POST['password'];


    //Creating respose array
    $respose = array("tag" => $tag, "success" => 1, "error" =>0);

    //Getting data from json
    //$username='asanka102';
    //$password='asanka102';

    //Querying mysql database against userauth table for user auth
    $sql = "SELECT * FROM userauth WHERE username='$username' AND password='$password'";
    $qry = mysql_query($sql);
    $fin_result = mysql_num_rows($qry);

    //Returning true when user exists & return false when user doen's exist
    //if$fin_result > 0(){
    //  return true;
    //}else{
    //  return false;
    //}
    if($fin_result > 0){
        //User found, login should be granted
        $response["success"] = 1;
        echo json_encode($response);
    }else{
        //User not found, login shold be prohibited
        $response["error"] = 0;
        $response["error_msg"] = 'Invalid login';
        echo json_encode($response);
    }


?>

MainActivity.java

public class MainActivity extends Activity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        etUsername = (EditText) findViewById(R.id.et_username);
        etPass = (EditText) findViewById(R.id.et_password);

        errorTxt = (TextView) findViewById(R.id.text_invalid_input);

        loginButton = (Button) findViewById(R.id.button_login);
        loginButton.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub

                new GetPassword().execute();


            }
        });

    }



    private class GetPassword extends AsyncTask<Void, Void, Void> {

        @Override
        protected Void doInBackground(Void... arg0) {

            String username = etUsername.getText().toString();
            String password = etPass.getText().toString();
            UserFunctions userFunctions = new UserFunctions();
            JSONObject json = userFunctions.loginUser(username, password);

            //Do other things



            return null;
        }

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

        }

    }

UserFunctions.java

public class UserFunctions {

    private JSONParser jsonParser;

    private static String login_url = "http://192.168.100.172/android/userauth.php";

    public UserFunctions(){
        jsonParser = new JSONParser();
    }

    /**
     * function make Login Request
     * @param username
     * @param password
     * */
    public JSONObject loginUser(String username, String password){
        // Building Parameters
        List<NameValuePair> params = new ArrayList<NameValuePair>();
        params.add(new BasicNameValuePair("username", username));
        params.add(new BasicNameValuePair("password", password));
        JSONObject json = jsonParser.getJSONFromUrl(login_url, params);
        // return json
        // Log.e("JSON", json.toString());
        return json;
    }
}

JSONParser.java

public class JSONParser {

    static InputStream is = null;
    static JSONObject jObj = null;
    static String json = "";

    // constructor
    public JSONParser() {
        // Empty constructor
    }

    // function get json from url
    // by making HTTP POST or GET mehtod
    public JSONObject getJSONFromUrl(String url, List<NameValuePair> params) {

        // Making HTTP request
        try {
            // 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();

        } 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();
            Log.e("JSON", json);
        } 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;

    }

}

The logcat gives this

02-11 12:29:10.457: E/Buffer Error(13927): Error converting result java.lang.NullPointerException: lock == null
02-11 12:29:10.457: E/JSON Parser(13927): Error parsing data org.json.JSONException: End of input at character 0 of 
02-11 12:29:10.457: W/dalvikvm(13927): threadid=11: thread exiting with uncaught exception (group=0x41ba5ba8)
02-11 12:29:10.467: D/dalvikvm(13927): GC_FOR_ALLOC freed 280K, 2% free 17142K/17456K, paused 10ms, total 11ms
02-11 12:29:10.477: E/AndroidRuntime(13927): FATAL EXCEPTION: AsyncTask #1
02-11 12:29:10.477: E/AndroidRuntime(13927): Process: collector.lbfinance, PID: 13927
02-11 12:29:10.477: E/AndroidRuntime(13927): java.lang.RuntimeException: An error occured while executing doInBackground()
02-11 12:29:10.477: E/AndroidRuntime(13927):    at android.os.AsyncTask$3.done(AsyncTask.java:300)
02-11 12:29:10.477: E/AndroidRuntime(13927):    at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355)
02-11 12:29:10.477: E/AndroidRuntime(13927):    at java.util.concurrent.FutureTask.setException(FutureTask.java:222)
02-11 12:29:10.477: E/AndroidRuntime(13927):    at java.util.concurrent.FutureTask.run(FutureTask.java:242)
02-11 12:29:10.477: E/AndroidRuntime(13927):    at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
02-11 12:29:10.477: E/AndroidRuntime(13927):    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
02-11 12:29:10.477: E/AndroidRuntime(13927):    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
02-11 12:29:10.477: E/AndroidRuntime(13927):    at java.lang.Thread.run(Thread.java:841)
02-11 12:29:10.477: E/AndroidRuntime(13927): Caused by: java.lang.NullPointerException
02-11 12:29:10.477: E/AndroidRuntime(13927):    at collector.lbfinance.MainActivity$GetPassword.doInBackground(MainActivity.java:102)
02-11 12:29:10.477: E/AndroidRuntime(13927):    at collector.lbfinance.MainActivity$GetPassword.doInBackground(MainActivity.java:1)
02-11 12:29:10.477: E/AndroidRuntime(13927):    at android.os.AsyncTask$2.call(AsyncTask.java:288)
02-11 12:29:10.477: E/AndroidRuntime(13927):    at java.util.concurrent.FutureTask.run(FutureTask.java:237)
02-11 12:29:10.477: E/AndroidRuntime(13927):    ... 4 more

Answer 1

Is $fin_result returning rows?

Try the following

try {
        BufferedReader reader = new BufferedReader(new InputStreamReader(
                is, "utf-8"), 8);
        StringBuilder sb = new StringBuilder();
        String line = null;
        while ((line = reader.readLine()) != null) {
            sb.append(line + "\n");
        }
        is.close();
        json = sb.toString();
        Log.e("JSON", json);
    } 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;

Answer 2

What does the logcat say by your is.close(); json = sb.toString(); Log.e("JSON", json); which is in JSONParser.java.