AppController

public class AppController extends Application {

    private static final String TAG = AppController.class.getSimpleName();
    private static AppController instance;
    RequestQueue mRequestQueue;

    @Override
    public void onCreate() {
        super.onCreate();
        instance = this;
    }

    public static synchronized AppController getInstance() {
        return instance;
    }

    private RequestQueue getRequestQueue() {
        if (mRequestQueue == null)
        {
            mRequestQueue = Volley.newRequestQueue(getApplicationContext());
        }

        return mRequestQueue;
    }

    public <T> void addToRequestQueue(Request<T> req, String tag) {
        req.setTag(TextUtils.isEmpty(tag) ? TAG : tag);
        getRequestQueue().add(req);
    }

    public <T> void addToRequestQueue (Request<T> req) {
        req.setTag(TAG);
        getRequestQueue().add(req);
    }

    public void cancelAllRequest(Object req) {
        if (mRequestQueue != null) {
            mRequestQueue.cancelAll(req);
        }
    }
}