public function prepareCallback($callback)
    {
        $result       = $callback;
        if (is_string($callback) && ($callbackInfo = $this->parseHandlerStr($callback))
            && class_exists($callbackInfo['class']) && method_exists(($controller
                = new $callbackInfo['class']), $callbackInfo['method'])) {
            $result = [$controller, $callbackInfo['method']];
        } elseif (!is_callable($callback)) {
            throw new \pwf\exception\HttpNotFoundException();
        }
        return $result;
    }