public static function isJson($string)
    {
        if (!is_string($string) || (is_string($string)
                && substr($string, 0, 1) !== '{'
                && substr($string, 0, 1) !== '[')
        ) {
            return false;
        }
        @json_decode($string);
        return (json_last_error() == JSON_ERROR_NONE);
    }