实现和使用示例：
``` * class My_Filter implements PhalApi_Filter { * * public function check() { * //TODO * } * } * * //$ vim ./Public/init.php * //注册签名验证服务 * DI()->filter = 'Common_SignFilter'; ``` * * @package PhalApi\Filter * @license http://www.phalapi.net/license GPL 协议 * @link http://www.phalapi.net/ * @author dogstar 2014-10-25 */ interface PhalApi_Filter { public function check(); }