获取当前网站二级域名方法

直接上代码：

/**
     * 获取二级域名 如.test.com
     * 
     * @staticvar type $domain
     * @return type
     */
    public static function getSecondDomain() {
        static $domain;
        if (empty($domain)) {
            $domain = $_SERVER['HTTP_HOST'];
        }
        $domainArray = explode('.', $domain);
        if (count($domainArray) === 2) {//test.com
            $domain = '.' . $domain;
        } elseif (count($domainArray) === 3) {//www.test.com
            $domain = '.' . $domainArray[1] . '.' . $domainArray[2];
        }else{//www.test.com.cn
            $domain = substr($domain,strpos($domain, '.'));
        }
        return $domain;
    }