Restful API Integration on Android

MainActivity.java

...
protected onCreate(Bundle savedStateInstance) {
  NetworkTask task = new NetworkTask(this);
  NetworkTask.execute();
}

public void successful(List<Repo> repos) {
  // do something
}
public void fail(Exception e) {
  // do something
}
...

NetworkTask.java

public class NetworkTask extends AsyncTask<Void, Void, String> {
  private Callback callback;
  public interface Callback {
    public void successful(List<Repo> repos);
    public void fail(Exception e);
  }

  public NetworkTask(Callback callback) {
    this.callback = callback;
  }
  protected Void doInBackground (Void.. params) {
    // we hard code here, because it should be re-design more interface if we want to support different type of parameter.
    String url =  "http://example.com/users/PRADA/repos?limit=10";
    HttpGet request = new HttpGet(url);
    AndroidHttpClient client = AndroidHttpClient.newInstance("Android");
    try {
      HttpResponse response = client.execute(request);
      HttpEntity entity = response.getEntity();
      return EntityUtils.toString(entity);
    } catch (Exception e) {
      return null;
    } finally {
      client.close();
    }
  }
  protected void onPostExecute (String result) {
    if (callback != null) {
      if (result == null) {
        callback.fail(new Exception());
      } else {
        callback.successful(parseJsonString(result));
      }
    }
  }

  private List<Repo> parseJsonString(String json) {
    // TODO
  }
}