public function getExt()
    {
        if (is_null($this->ext) && $this->originFile) {
            $file = basename($this->originFile);
            // Use substr instead of pathinfo, because pathinfo may return error value in unicode
            if (false !== $pos = strrpos($file, '.')) {
                $this->ext = strtolower(substr($file, $pos + 1));
            } else {
                $this->ext = '';
            }
        }
        return $this->ext;
    }