android - Not getting json data into mapview, getting blank map only

Possible Duplicate:
android.os.NetworkOnMainThreadException

i am fetching JSON data into MapView to show locations, but whenever i run my program not getting data into Map just getting blank map without json data, here i am placing my json data and Activity Code, please tell me where i am doing mistake
{
"maps": [
{

"title": "Place One",
"latitude" : "46.483742",

"longitude" : "7.663157",
"country": "Switzerland"
},
{
"title" : "Place Two",
"latitude" : "59.25235",
"longitude" : "18.465536",
"country" : "Sweden"
},
{

"title" : "Place Three",
"latitude" : "56.404182",
"longitude" : "-3.818855",
"country" : "Scotland"
}
]
}

Activity Code:-

public class Main extends MapActivity {
public GeoPoint point;
TapControlledMapView mapView; // use the custom TapControlledMapView
List mapOverlays;
Drawable drawable;
SimpleItemizedOverlay itemizedOverlay;

@Override
public void onCreate(final Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    mapView = (TapControlledMapView) findViewById(R.id.mapview);
    mapView.setBuiltInZoomControls(true);
    mapView.setSatellite(false);
    // dismiss balloon upon single tap of MapView (iOS behavior) 
    mapView.setOnSingleTapListener(new OnSingleTapListener() {      
        public boolean onSingleTap(MotionEvent e) {
            itemizedOverlay.hideAllBalloons();

            return true;

        }
    });

    mapOverlays = mapView.getOverlays();        
    drawable = getResources().getDrawable(R.drawable.ic_launcher);
    itemizedOverlay = new SimpleItemizedOverlay
            (drawable, mapView);        
    itemizedOverlay.setShowClose(false);

    itemizedOverlay.setShowDisclosure(true);
    itemizedOverlay.setSnapToCenter(false);

     class DownloadWebPageTask extends AsyncTask {
        @Override
        protected String doInBackground(String... urls) {

    HttpClient client = new DefaultHttpClient();
    // Perform a GET request for a JSON list
    HttpUriRequest request = new HttpGet

            ("https://dl.!!!!.com/maps.json");
    // Get the response that sends back
    HttpResponse response = null;
    try {
        response = client.execute(request);
    } catch (ClientProtocolException e1) {
        // TODO Auto-generated catch block
        e1.printStackTrace();
    } catch (IOException e1) {
        // TODO Auto-generated catch block

        e1.printStackTrace();
    }
    // Convert this response into a readable string
    String jsonString = null;
    try {
        jsonString = StreamUtils.convertToString
                (response.getEntity().getContent());
    } catch (IllegalStateException e1) {
        // TODO Auto-generated catch block
        e1.printStackTrace();

    } catch (IOException e1) {
        // TODO Auto-generated catch block
        e1.printStackTrace();
    }
    // Create a JSON object that we can use from the String
    JSONObject json = null;
    try {
        json = new JSONObject(jsonString);
    } catch (JSONException e1) {
        // TODO Auto-generated catch block

        e1.printStackTrace();
    }


               try{

     JSONArray jsonArray = json.getJSONArray("maps");
     Log.e("log_tag", "Opening JSON Array ");
        for(int i=0;i < jsonArray.length();i++)
            {                       


            JSONObject jsonObject = jsonArray.getJSONObject(i);

                String latitude =  jsonObject.getString("latitude");
                String longitude =  jsonObject.getString("longitude");
                String title =  jsonObject.getString("title");
                String country = jsonObject.getString("country");


                double lat = Double.parseDouble(latitude);

                double lng = Double.parseDouble(longitude);


                     Log.e("log_tag", "ADDING GEOPOINT"+title); 

                      point = new GeoPoint(
                             (int) (lat * 1E6), 
                             (int) (lng * 1E6));
                    OverlayItem overlayItem = new OverlayItem(point, title, 
                            country);

                    itemizedOverlay.addOverlay(overlayItem);

                    }
               }catch(JSONException e)        {
                 Log.e("log_tag", "Error parsing data "+e.toString());
            } 

               itemizedOverlay.populateNow(); 

               mapOverlays.add(itemizedOverlay);

                    if (savedInstanceState == null) {
            MapController controller = mapView.getController();
                        controller.setCenter(point);
                        controller.setZoom(7);

                    } else {

              // example restoring focused state of overlays
                        int focused;
                focused = savedInstanceState.getInt("focused_1", -1);

            if (focused >= 0) {
                              itemizedOverlay.setFocus
                       (itemizedOverlay.getItem(focused));
                        }
                    }
                    return jsonString;   }
     }

     }