JSON parser java.lang.NullPointerException

Question

im getting this error, trying to build a JSON parser with a ListView. I tried this code with another JSON source and it works but with this link crashes: http://earthquake.usgs.gov/earthquakes/feed/v1.0/summary/all_day.geojson

I´d love some help :D

Error:

05-21 20:53:32.871 2509-2606/com.ikeres.app.professorearthquake     W/System.err: org.json.JSONException: End of input at character 0 of 
05-21 20:53:32.872 2509-2606/com.ikeres.app.professorearthquake    W/System.err:     at org.json.JSONTokener.syntaxError(JSONTokener.java:449)
05-21 20:53:32.872 2509-2606/com.ikeres.app.professorearthquake W/System.err:     at org.json.JSONTokener.nextValue(JSONTokener.java:97)
05-21 20:53:32.872 2509-2606/com.ikeres.app.professorearthquake W/System.err:     at org.json.JSONObject.<init>(JSONObject.java:156)
05-21 20:53:32.872 2509-2606/com.ikeres.app.professorearthquake W/System.err:     at org.json.JSONObject.<init>(JSONObject.java:173)
05-21 20:53:32.872 2509-2606/com.ikeres.app.professorearthquake W/System.err:     at    com.ikeres.app.professorearthquake.MainActivity.ParseJSON(MainActivity.java:102)
05-21 20:53:32.872 2509-2606/com.ikeres.app.professorearthquake  W/System.err:     at   com.ikeres.app.professorearthquake.MainActivity.access$200(MainActivity.java:19)
05-21 20:53:32.872 2509-2606/com.ikeres.app.professorearthquake  W/System.err:     at  com.ikeres.app.professorearthquake.MainActivity$GetTerremotos.doInBackground(Mai nActivity.java:70)
05-21 20:53:32.872 2509-2606/com.ikeres.app.professorearthquake  W/System.err:     at  com.ikeres.app.professorearthquake.MainActivity$GetTerremotos.doInBackground(Mai nActivity.java:44)
05-21 20:53:32.872 2509-2606/com.ikeres.app.professorearthquake  W/System.err:     at android.os.AsyncTask$2.call(AsyncTask.java:295)
05-21 20:53:32.872 2509-2606/com.ikeres.app.professorearthquake W/System.err:     at java.util.concurrent.FutureTask.run(FutureTask.java:237)
05-21 20:53:32.872 2509-2606/com.ikeres.app.professorearthquake W/System.err:     at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:234)
05-21 20:53:32.872 2509-2606/com.ikeres.app.professorearthquake W/System.err:     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113)
05-21 20:53:32.872 2509-2606/com.ikeres.app.professorearthquake  W/System.err:     at  java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588)
05-21 20:53:32.872 2509-2606/com.ikeres.app.professorearthquake W/System.err:         at java.lang.Thread.run(Thread.java:818)

Here is the MainActivity:

public class MainActivity extends ListActivity {

// URL to get contacts JSON
private static String url = "http://earthquake.usgs.gov/earthquakes/feed/v1.0/summary/all_day.geojson";

// JSON Node names
private static final String TAG_FEATURES = "features";
private static final String TAG_PROPERTIES = "properties";
private static final String TAG_LUGAR = "lugar";
private static final String TAG_MAGNITUD = "magnitud";
private static final String TAG_HORA = "hora";


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    // Calling async task to get json
    new GetTerremotos().execute();
}

/**
 * Async task class to get json by making HTTP call
 */
private class GetTerremotos extends AsyncTask<Void, Void, Void> {

    // Hashmap for ListView
    ArrayList<HashMap<String, String>> terremotostList;
    ProgressDialog pDialog;

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        // Showing progress dialog
        pDialog = new ProgressDialog(MainActivity.this);
        pDialog.setMessage("Please wait...");
        pDialog.setCancelable(false);
        pDialog.show();
    }

    @Override
    protected Void doInBackground(Void... arg0) {
        // Creating service handler class instance
        WebRequest webreq = new WebRequest();

        // Making a request to url and getting response
        String jsonStr = webreq.makeWebServiceCall(url, WebRequest.GET);

        Log.d("Response: ", "> " + jsonStr);

        terremotostList = ParseJSON(jsonStr);

        return null;
    }

    @Override
    protected void onPostExecute(Void result) {
        super.onPostExecute(result);
        // Dismiss the progress dialog
        if (pDialog.isShowing())
            pDialog.dismiss();
        /**
         * Updating parsed JSON data into ListView
         * */
        ListAdapter adapter = new SimpleAdapter(
                MainActivity.this, terremotostList,
                R.layout.list_item, new String[]{TAG_LUGAR, TAG_MAGNITUD,
                TAG_HORA}, new int[]{R.id.name,
                R.id.email, R.id.mobile});

        setListAdapter(adapter);
    }

}

private ArrayList<HashMap<String, String>> ParseJSON(String json) {
    if (json != null) {
        try {
            // Hashmap for ListView
            ArrayList<HashMap<String, String>> studentList = new ArrayList<HashMap<String, String>>();

            JSONObject jsonObj = new JSONObject(json);

            // Getting JSON Array node
            JSONArray terremotos = jsonObj.getJSONArray(TAG_FEATURES);

            // looping through All HeartQuakes
            for (int i = 0; i < terremotos.length(); i++) {
                JSONObject c = terremotos.getJSONObject(i);




                // Properties node is JSON Object
                JSONObject properties = c.getJSONObject(TAG_PROPERTIES);
                String lugar = properties.getString(TAG_LUGAR);
                String magnitud = properties.getString(TAG_MAGNITUD);
                String hora = properties.getString(TAG_HORA);

                // tmp hashmap for single hq
                HashMap<String, String> oterremoto = new HashMap<String, String>();

                // adding each child node to HashMap key => value
                oterremoto.put(TAG_LUGAR, lugar);
                oterremoto.put(TAG_MAGNITUD, magnitud);
                oterremoto.put(TAG_HORA, hora);


                // adding student to hq list
                studentList.add(oterremoto);
            }
            return studentList;
        } catch (JSONException e) {
            e.printStackTrace();
            return null;
        }
    } else {
        Log.e("ServiceHandler", "Couldn't get any data from the url");
        return null;
    }
}

}

WebRequest class:

public class WebRequest {

static String response = null;
public final static int GET = 1;
public final static int POST = 2;

//Constructor with no parameter
public WebRequest() {

}

/**
 * Making web service call
 *
 * @url - url to make request
 * @requestmethod - http request method
 */
public String makeWebServiceCall(String url, int requestmethod) {
    return this.makeWebServiceCall(url, requestmethod, null);
}

/**
 * Making service call
 *
 * @url - url to make request
 * @requestmethod - http request method
 * @params - http request params
 */
public String makeWebServiceCall(String urladdress, int requestmethod,
                                 HashMap<String, String> params) {
    URL url;
    String response = "";
    try {
        url = new URL(urladdress);

        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setReadTimeout(15000);
        conn.setConnectTimeout(15000);
        conn.setDoInput(true);
        conn.setDoOutput(true);

        if (requestmethod == POST) {
            conn.setRequestMethod("POST");
        } else if (requestmethod == GET) {
            conn.setRequestMethod("GET");
        }

        if (params != null) {
            OutputStream os = conn.getOutputStream();
            BufferedWriter writer = new BufferedWriter(
                    new OutputStreamWriter(os, "UTF-8"));

            StringBuilder result = new StringBuilder();
            boolean first = true;
            for (Map.Entry<String, String> entry : params.entrySet()) {
                if (first)
                    first = false;
                else
                    result.append("&");

                result.append(URLEncoder.encode(entry.getKey(), "UTF-8"));
                result.append("=");
                result.append(URLEncoder.encode(entry.getValue(), "UTF-8"));
            }

            writer.write(result.toString());

            writer.flush();
            writer.close();
            os.close();
        }

        int responseCode = conn.getResponseCode();

        if (responseCode == HttpsURLConnection.HTTP_OK) {
            String line;
            BufferedReader br = new BufferedReader(new InputStreamReader(conn.getInputStream()));
            while ((line = br.readLine()) != null) {
                response += line;
            }
        } else {
            response = "";
        }
    } catch (Exception e) {
        e.printStackTrace();
    }

    return response;
}

}

Answer 1

Finally got it. Remove the following lines from the WebRequest class:

    conn.setDoInput(true);
    conn.setDoOutput(true);

add the following after conn.setRequestMethod("GET");:

conn.connect();

Now you get JSON out of the API. After that your app would not display anything. That's because your tags are all in spanish and the API is in english so change:

private static final String TAG_LUGAR = "lugar";
private static final String TAG_MAGNITUD = "magnitud";
private static final String TAG_HORA = "hora";

to:

private static final String TAG_LUGAR = "place";
private static final String TAG_MAGNITUD = "mag";
private static final String TAG_HORA = "time";

It works after these changes.

Answer 2

You need to check for fields existence when parsing your json. Your code fails at this line:

String lugar = properties.getString(TAG_LUGAR);

because there is no such field lugar in the returned json. So this line throws an exception, which is catched with this code:

catch (JSONException e) {
        e.printStackTrace();
        return null;
    }

and returns NULL. Then, you are creating an adapter and passing a null object:

ListAdapter adapter = new SimpleAdapter(
            MainActivity.this, terremotostList,
            R.layout.list_item, new String[]{TAG_LUGAR, TAG_MAGNITUD,
            TAG_HORA}, new int[]{R.id.name,
            R.id.email, R.id.mobile});

(terremotostList is null)

and finally your adapter fails trying to access getCount method of your list, which is null.

How to solve this problem? You should either check for field existence before getting its value:

String lugar = properties.has(TAG_LUGAR) ? properties.getString(TAG_LUGAR) : null;

or just use optString method, which doesn't throw an exception if field doesn't exist:

String lugar = properties.optString(TAG_LUGAR);