How to get integer from json object async in android?

Question

Original Question -

I was following a tutorial on json in android, but having problem to get json value using Async in android. First I created jsonparser class and added following to it -

    public JSONObject getJSONFromUrl(String url) {

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

    // 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;
}

Then to use this in fragment by async i tried -

    class getTopicId extends AsyncTask<String, String, JSONObject> {
    private ProgressDialog pDialog;
    @Override
      protected void onPreExecute() {
          super.onPreExecute();
          pDialog = new ProgressDialog(getActivity());
          pDialog.setMessage("Getting Topic of the Day ...");
          pDialog.setIndeterminate(false);
          pDialog.setCancelable(true);
          pDialog.show();
    }
    @Override
      protected JSONObject doInBackground(String... args) {
      JSONParser jParser = new JSONParser();
      // Getting JSON from URL
      JSONObject json = jParser.getJSONFromUrl("http://medicalguru.in/android/tod.php");
      return json;
    }
     @Override
       protected void onPostExecute(JSONObject json) {
       pDialog.dismiss();
       try {
           topic_id = json.getInt("value");    
      } 
       catch (JSONException e) {
        e.printStackTrace();
      }
       finally {
           Toast.makeText(getActivity(), "topic id -"+topic_id, Toast.LENGTH_LONG).show();
       }
     }
}

but the app is crashing when i execute this async. my logcat shows -

03-06 15:07:03.123: E/AndroidRuntime(2041): FATAL EXCEPTION: main
03-06 15:07:03.123: E/AndroidRuntime(2041): java.lang.NullPointerException
03-06 15:07:03.123: E/AndroidRuntime(2041):     at in.medicalguru.DailyTestFragment$getTopicId.onPostExecute(DailyTestFragment.java:786)
03-06 15:07:03.123: E/AndroidRuntime(2041):     at in.medicalguru.DailyTestFragment$getTopicId.onPostExecute(DailyTestFragment.java:1)
03-06 15:07:03.123: E/AndroidRuntime(2041):     at android.os.AsyncTask.finish(AsyncTask.java:631)
03-06 15:07:03.123: E/AndroidRuntime(2041):     at android.os.AsyncTask.access$600(AsyncTask.java:177)
03-06 15:07:03.123: E/AndroidRuntime(2041):     at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:644)
03-06 15:07:03.123: E/AndroidRuntime(2041):     at android.os.Handler.dispatchMessage(Handler.java:99)
03-06 15:07:03.123: E/AndroidRuntime(2041):     at android.os.Looper.loop(Looper.java:137)
03-06 15:07:03.123: E/AndroidRuntime(2041):     at android.app.ActivityThread.main(ActivityThread.java:5103)
03-06 15:07:03.123: E/AndroidRuntime(2041):     at java.lang.reflect.Method.invokeNative(Native Method)
03-06 15:07:03.123: E/AndroidRuntime(2041):     at java.lang.reflect.Method.invoke(Method.java:525)
03-06 15:07:03.123: E/AndroidRuntime(2041):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
03-06 15:07:03.123: E/AndroidRuntime(2041):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
03-06 15:07:03.123: E/AndroidRuntime(2041):     at dalvik.system.NativeStart.main(Native Method)

The link mentioned above in the code outputs as -

{"value":1}

when opened normally, but when I run in async it says err related to nullpointer? Couldn't figure, where I am making mistake ?

---

Edit 1 : *tod.php* code (Since Matthew has pointed something which I dont understand, so it may be helpful)

<?php
$today = date("Ymd");
switch($today){
case 20140304 :
$tod["value"] = 24;
break;
case 20140305 :
$tod["value"] = 25;
break;
case 20140306 :
$tod["value"] = 1;
break;
default:
$tod["value"] = 1;
break;
}
echo json_encode($tod);
?>

---

Edit 2 : *Found the problem (fully for me) but Partly in Real* - A special thanks to Matthew for his idea, to uncomment the error logs of function getJSONFromUrl(String url). I got a new error line in logcat -

Error parsing data org.json.JSONException: Value  of type java.lang.String cannot be converted to JSONObject

After little bit of search on google and stacksoverflow I found one suggestion to change chrSet to UTF-8 instead of iso-8859-1. and it worked for my requested url in both situations (with or without WWW - suggestion to test, by nikis). But this answer is partial real, because, now 2 unanswered questions developed - 1. Why did chrSet change worked? In future, what chrSet to be used, to avoid this problem, and what's the use of other one chrSet? 2. Matthew has replicated my Json to his server mwesly.com/test/ . Trial on his server, logcat shows following error in all cases (with or without WWW, with or without using index.php in the end) -

Error parsing data org.json.JSONException: Value <!DOCTYPE of type java.lang.String cannot be converted to JSONObject

Now, why is this error appearing on his server? What should be done to prevent/treat this error. If I need to ask these updated questions separately, please let me know.

Answer 1

It looks like json is null on following line, which is giving you the NullPointerException.

topic_id = json.getInt("value");

I think this is because your parser is having issues parse the json. I wrote a quick python script and tried to parse the page and it failed as well. For some reason, the response I get from http://medicalguru.in/android/tod.php is:

\xef\xbb\xbf{"value":1}

I am not sure why the \xef\xbb\xbf bytes are there, but they are likely causing the problem.

edit: a quick google search says it is the UTF-8 BOM. If you remove it your android code should work.

edit2: I put an example json on http://mwesly.com/test. Try hitting that json to see if your android code is correct. If it works, it means there is a problem with your endpoint, not your android code.

edit3: example of using loopj:

AsyncHttpClient client = new AsyncHttpClient();
client.get("http://mwesly.com/test", null, new JsonHttpResponseHandler() {
    @Override
    public void onSuccess(JSONObject json) {
        // do something with the json
        int value = json.getInt("value");
    }
});

I'm going to head to bed, if you still haven't solved this problem when I wake up, I'll give it another look. Good luck and happy coding!

Answer 2

Try to use the following getJSONFromUrl method:

public JSONObject getJSONFromUrl(String url) {

    // Making HTTP request
    try {
        // defaultHttpClient
        DefaultHttpClient httpClient = new DefaultHttpClient();
        HttpPost httpPost = new HttpPost(url);
        HttpResponse httpResponse = httpClient.execute(httpPost);
        return new JSONObject(EntityUtils.toString(httpResponse.getEntity()));
    } catch (UnsupportedEncodingException e) {
        e.printStackTrace();
    } catch (ClientProtocolException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
    return null;
}

Answer 3

private JSONObject jObj = null;
private JSONArray JArr = null;

and then after;

        URL url = null;
        try {
            url = new URL("your url is here");
        } catch (MalformedURLException e1) {
            // TODO Auto-generated catch block
            e1.printStackTrace();
        }

        JSONParser jParser = new JSONParser();
        String json_value = jParser.getJSONFromUrl(url);
    try {
              JArr = new JSONArray(json_value);
            } catch (JSONException e) {
                e.printStackTrace();
            }
            jObj = null;

            for (int i = 0; i < JArr.length(); i++) {
                try {
                    jObj = JArr.getJSONObject(i);
                    topic_id = jObj.getInt("value");
                } catch (JSONException e) {
                    e.printStackTrace();
                }
            }