java.lang.RuntimeException error occured while executing doInBackground()
<p>I beginner in android development, getting error in following code. i am calling asyn method for http request.Its giving me java.lang.RuntimeException error occured while executing doInBackground()</p>

<pre><code>private class PostAlert extends AsyncTask&lt;String, Integer, JSONArray&gt;{

    private ProgressDialog progressDialog;

    @Override
    protected JSONArray doInBackground(String... params) {
        // TODO Auto-generated method stub
        JSONArray menuitemArr = null;
        String url=params[0];

        System.out.println("fsfsddddf"+params[0]);
        ControlDashboard obj = new ControlDashboard();
        try{
        JSONObject aobj = obj.getJSONFromUrl(url);

            JSONObject array = aobj.getJSONObject("alert_list");    
             menuitemArr = array.getJSONArray("array");

        }   
        catch (JSONException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }       

        return menuitemArr;
    }

    @Override
    protected void onPostExecute(JSONArray menuitemArr) {
        // TODO Auto-generated method stub
        super.onPostExecute(menuitemArr);
        if (menuitemArr.length() == 0) {
            startActivity(new Intent("com.example.mysampleapp.ABOUT"));
            //Toast.makeText(Alert.this, "No Alerts", Toast.LENGTH_LONG).show();
        }else{
        name = new String[menuitemArr.length()];
        alert = new String[menuitemArr.length()];
        date = new String[menuitemArr.length()];
        for (int i = 0; i &lt; menuitemArr.length(); i++) { 
            // printing the values to the logcat 
            try {
                name[i] =  menuitemArr.getJSONObject(i).getString("name").toString();
                alert[i] = menuitemArr.getJSONObject(i).getString("message").toString(); 
                date[i] = menuitemArr.getJSONObject(i).getString("date").toString();
            } catch (JSONException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } 

        } 
        ListView list = (ListView) findViewById(R.id.listView3);
        ArrayList&lt;HashMap&lt;String, String&gt;&gt; mylistData = new ArrayList&lt;HashMap&lt;String, String&gt;&gt;();
        String[] columnTags = new String[] {"col1", "col2", "col3"};
        int[] columnIds = new int[] {R.id.alert1, R.id.alert2, R.id.alert3};
        for(int i=0; i&lt;name.length; i++)
        {
         HashMap&lt;String,String&gt; map = new HashMap&lt;String, String&gt;();
             map.put("col1", name[i]);
             map.put("col2", alert[i]);
             map.put("col3", date[i]);
         mylistData.add(map);
        }
        SimpleAdapter arrayAdapter = new SimpleAdapter(Alert.this, mylistData, R.layout.alert_view,columnTags,columnIds);
        list.setAdapter(arrayAdapter);      
        }
    }

    @Override
    protected void onPreExecute() {
        // TODO Auto-generated method stub
        super.onPreExecute();
        progressDialog = new ProgressDialog(Alert.this);
        progressDialog.setProgressStyle(ProgressDialog.STYLE_SPINNER);
        progressDialog.setMessage("please wait...");
        progressDialog.setCancelable(false);
        progressDialog.setIndeterminate(false);
        progressDialog.setMax(100);
        progressDialog.setProgress(0);
        progressDialog.show();
    }

    @Override
    protected void onProgressUpdate(Integer... values) {
        // TODO Auto-generated method stub
        super.onProgressUpdate(values);
        //progressDialog.dismiss();
    }



}
</code></pre>

<p>Error when i run my android application.</p>

<pre><code>12-17 13:22:48.035: W/dalvikvm(1160): threadid=8: thread exiting with uncaught exception (group=0x4001d800)
12-17 13:22:48.045: E/AndroidRuntime(1160): FATAL EXCEPTION: AsyncTask #2
12-17 13:22:48.045: E/AndroidRuntime(1160): java.lang.RuntimeException: An error occured while executing doInBackground()
12-17 13:22:48.045: E/AndroidRuntime(1160):     at android.os.AsyncTask$3.done(AsyncTask.java:200)
12-17 13:22:48.045: E/AndroidRuntime(1160):     at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
12-17 13:22:48.045: E/AndroidRuntime(1160):     at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
12-17 13:22:48.045: E/AndroidRuntime(1160):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
12-17 13:22:48.045: E/AndroidRuntime(1160):     at java.util.concurrent.FutureTask.run(FutureTask.java:137)
</code></pre>

<p>json request class:</p>

<pre><code>public class ControlDashboard extends Activity {
    public static DefaultHttpClient httpClient;

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

    public JSONObject getJSONFromUrl(String url) {

        // 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());
        }

        // try parse the string to a JSON object
        try {
            jObj = new JSONObject(json);
        } catch (JSONException e) {
            jObj = null;
            Log.e("JSON Parser", "Error parsing data " + e.toString());
        }

        // return JSON String
        return jObj;

    }



}
</code></pre>
