public function setClassName($className)
    {
        try {
            $classFilename = ClassLoader::getInstance()->findClass($className);
            if (!file_exists($classFilename)) {
                throw new BootstrapException('The provided callback class "' . $className . '" does not exist.');
            } else {
                $this->className = $className;
            }
        } catch (\Exception $e) {
            throw $e;
        }
    }