控制器不存在:app\index\controller\sitemap\Xml

            ->setAction($this->actionName);
    }

    public function exec()
    {
        try {
            // 实例化控制器
            $instance = $this->controller($this->controller);
        } catch (ClassNotFoundException $e) {
            throw new HttpException(404, 'controller not exists:' . $e->getClass());
        }

        // 注册控制器中间件
        $this->registerControllerMiddleware($instance);

        return $this->app->middleware->pipeline('controller')
            ->send($this->request)
            ->then(function () use ($instance) {
                // 获取当前操作名