php 字符过滤类，用于过滤各类用户输入的数据

<?php 
abstract class Filter { //filter parent class 
private $blackstr = array(); 
private $whitestr = array(); 
function filtit($str) { 
//do something 
} 
} 
class LoginFilter extends Filter { //for user login filte username(过滤注册的用户名) 
function filtit($str) { 
$this -> blackstr = array( 
´/[\x7f-\xff]/´, //filter chinese include chinese symbol 
´/\W/´ //filter all english symbol 
); 
return preg_replace($this->blackstr, ´´, $str); 
} 
} 
class EditorFilter extends Filter { //for article editor filter(过滤在线编辑器内容) 
function filtit($str) { 
$this -> blackstr = array( 
´/\&/´, 
´/\´/´, 
´/\"/´, 
´/\</´, 
´/\>/´, 
´/\\\\/´, 
´/\//´, 
´/-/´, 
´/\*/´, 
´/ /´ 
); 
$this -> whitestr = array( 
´&´, 
´'´, 
´"´, 
´<´, 
´>´, 
´\´, 
´/´, 
´-´, 
´*´, 
´ ´ 
); 
return preg_replace($this->blackstr, $this -> whitestr, $str); 
} 
} 
class SQLFilter extends Filter { //for filte sql query string(过滤如查询或其它sql语句) 
function filtit($str) { 
$this -> blackstr = array( 
´/\´/´, 
´/-/´ 
); 
return preg_replace($this->blackstr, ´´, $str); 
} 
} 
class FileNameFilter extends Filter { //for filte a file name(过滤文件名如下载文件名) 
function filtit($str) { 
$this -> blackstr = array( 
´/[^A-za-z0-9_\.]|\\\\|\^|\[|\]/´ 
); 
return preg_replace($this->blackstr, ´´, $str); 
} 
} 
?> 

$filter = new FileNameFilter(); //定义实例 
$downFile = $filter->filtit($_GET[´fn´]); //调用过滤方法