I have created a restful web service using this tutorial http://www.tutecentral.com/restful-api-for-android-part-1/ after running this i got an auto generated java file which contains the following code

public class RestAPI {

  private final String urlString = "http://10.0.2.2:58893/Handler1.ashx"; 
  private static String convertStreamToUTF8String(InputStream stream) throws IOException {
    String result = "";
    StringBuilder sb = new StringBuilder();
    try {
        InputStreamReader reader = new InputStreamReader(stream, "UTF-8");
        char[] buffer = new char[4096];
        int readedChars = 0;
        while (readedChars != -1) {
            readedChars = reader.read(buffer);
            if (readedChars > 0)
               sb.append(buffer, 0, readedChars);
        }
        result = sb.toString();
    } catch (UnsupportedEncodingException e){
        e.printStackTrace();
    }//
    return result;
}
private String load(String contents) throws IOException {
    URL url = new URL(urlString);
    Log.e("load r1","load r1");
    HttpURLConnection conn = (HttpURLConnection)url.openConnection();
    conn.setRequestMethod("POST");
    conn.setConnectTimeout(60000);
    Log.e("load r2","load r2");
    conn.setDoOutput(true);
    conn.setDoInput(true);
    Log.e("load r3","load r3");
    OutputStreamWriter w = new OutputStreamWriter(conn.getOutputStream());
    w.write(contents);
    w.flush();
    Log.e("load r4","load r4");
    InputStream istream = conn.getInputStream();
    Log.e("load r5","load r5");
    String result = convertStreamToUTF8String(istream);
    return result;
}

private Object mapObject(Object o) {
    Object finalValue = null;
    if (o.getClass() == String.class) {
        finalValue = o;
    }
    else if (Number.class.isInstance(o)) {
        finalValue = String.valueOf(o);
    } else if (Date.class.isInstance(o)) {
        SimpleDateFormat sdf = new SimpleDateFormat("MM/dd/yyyy hh:mm:ss", new Locale("en", "USA"));
        finalValue = sdf.format((Date)o);
    }
    else if (Collection.class.isInstance(o)) {
        Collection<?> col = (Collection<?>) o;
        JSONArray jarray = new JSONArray();
        for (Object item : col) {
            jarray.put(mapObject(item));
        }
        finalValue = jarray;
    } else {
        Map<String, Object> map = new HashMap<String, Object>();
        Method[] methods = o.getClass().getMethods();
        for (Method method : methods) {
            if (method.getDeclaringClass() == o.getClass()
                    && method.getModifiers() == Modifier.PUBLIC
                    && method.getName().startsWith("get")) {
                String key = method.getName().substring(3);
                try {
                    Object obj = method.invoke(o, null);
                    Object value = mapObject(obj);
                    map.put(key, value);
                    finalValue = new JSONObject(map);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }

    }
    return finalValue;
}

public JSONObject GetDoctors(String Terr&#95;Code) throws Exception {
    JSONObject result = null;
    JSONObject o = new JSONObject();
    JSONObject p = new JSONObject();
    o.put("interface","RestAPI");
    o.put("method", "GetDoctors");
    p.put("Terr&#95;Code",mapObject(Terr&#95;Code));
    o.put("parameters", p);
    String s = o.toString();
    String r = load(s);
    result = new JSONObject(r);
    return result;
}

public JSONObject GetUserDetail(String IMEINO) throws Exception {
    JSONObject result = null;
    JSONObject o = new JSONObject();
    JSONObject p = new JSONObject();
    o.put("interface","RestAPI");
    o.put("method", "GetUserDetail");
    p.put("IMEINO",mapObject(IMEINO));
    o.put("parameters", p);
    String s = o.toString();
    String r = load(s);
    result = new JSONObject(r);
    return result;
}


public JSONObject GetProductsForOrders(String ff&#95;code) throws Exception {
    JSONObject result = null;
    JSONObject o = new JSONObject();
    JSONObject p = new JSONObject();
    o.put("interface","RestAPI");
    o.put("method", "GetProductsForOrders");
    p.put("ff&#95;code",mapObject(ff&#95;code));
    o.put("parameters", p);
    String s = o.toString();
    String r = load(s);
    result = new JSONObject(r);
    return result;
}

}

I want to access the these method using volley as async task is very slow, but i don't understand how to call methods in volley code. I've tried in the below code but i get the error of "bad url null"

       public void requestJSON() {
          // Tag used to cancel the request
          String tag_json_obj = "json_obj_req";

          final ProgressDialog pDialog = new ProgressDialog(context);
          pDialog.setMessage("Loading...");
          pDialog.show();
          JsonObjectRequest jsonObjReq = new JsonObjectRequest(Method.GET, null,
                null, new Response.Listener<JSONObject>() {

                   @Override
                   public void onResponse(JSONObject response) {

                        RestAPI restAPI = new RestAPI();
                        try {
                              response = restAPI.GetDoctors(terrcode);                           
                        } 

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

                 display.setText(response.toString());
                       Log.e("json data",response.toString());
                      pDialog.hide();
                   }



              }, new Response.ErrorListener() {

                   @Override
                   public void onErrorResponse(VolleyError error) {
                      display.setText(error.toString());
                      pDialog.hide();
                   }
                });

          // Adding request to request queue
          VolleySingleton.getInstance().addToRequestQueue(jsonObjReq,
                tag&#95;json&#95;obj);
       }