PHP設計模式之調解者模式

<?php
abstract class Filter{
    abstract public function _filter($value);
}
class TrimFilter extends Filter{
    public function _filter($value){
        return trim($value);
    }
}
class HtmlFilter extends Filter{
    public function _filter($value) {
        return strip_tags($value);
    }
}
class NullFilter extends Filter{
    public function _filter($value) {
        return $value ? $value : '';
    }
}
class InputMediator{
    private $filters;
    private $value;
    public function addFilter(Filter $obj){
        $this->filters[] = $obj;
        return $this;
    }
    public function setValue($value){
        $this->value = $this->filter($value);
    }
    public function filter($value){
        foreach ($this->filters as $key=>$val){
            $value = $val->_filter($value);
        }
        return $value;
    }
    public function getValue(){
        return $this->value;
    }
}
$mediator = new InputMediator();
$mediator->addFilter(new HtmlFilter())->addFilter(new NullFilter())->addFilter(new TrimFilter());
$mediator->setValue(" <script>alert('ok')</script>");
echo $mediator->getValue();