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PHP设计模式之调解者模式的深入解析_PHP

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Release: 2016-06-01 12:06:29
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调解者模式,这个模式的目的是封装一组对象之间的相互作用,防止对象之间相互干扰,调解者(Mediator)在同事对象(Colleague)之间充当中间汇聚点。同事对象之间应该保持松散耦合,避免一个对象直接明确指向另一个对象。在调解者模式下,对象的关系和依赖发生冲突时,我们可以使用调解者在耦合的对象之间协调工作流,依赖可以从同事朝调解者或从调解者向同事建立,这两个方向上的依赖都可以使用AbstractColleague或AbstractMediator中断。



对象不是孤立的,对象之间必须相互协作才能完成任务。虽然调解者模式可以限制对象之间的相互作用,但如果滥用,会致使编写聚合性类变得非常困难。举一个实用的例子,在领域驱动设计(Domain-Driven Design)中的服务就是实体之间的调解者。再举一个PHP相关的例子,Zend_Form装饰和过滤功能实际上可以看作是Zend_Form_Decorator和Zend_Filter实例之间的一个简单调解者,它们都使用Zend_Validate对象进行验证。

当调解者必须监听同事对象的事件时,它通常是作为观察者(Observer)实现的,产生一个黑板(blackboard)对象,一些同事写,另一些同事就读。来自同事的事件被推向调解者,再由调解者将其转发给其它订阅的同事,同事之间不需要相互了解,这个架构成功用于随Zend框架发布的Dojo JavaScript库。这个模式的另一个好处是对象的变化包含在计算方法中,可以通过配置不同的调解者实现这一目标,但实例化相关对象将是一个松散的操作,不同容器和工厂之间的协作关系将是分散的。

参与者:
◆同事(Colleague):重点是它的职责,它只与一个调解者Mediator或AbstractMediator通信。
◆调解者(Mediator):协同多个Colleagues(AbstractColleagues)共同工作。
◆AbstractMediator,AbstractColleague:从这些角色的真实实现解耦的可选接口,可能不止一个AbstractColleague角色。
下面的代码实现了一个表单输入的过滤过程,类似于Zend_Form_Element功能。
复制代码 代码如下:
        /** 
     * AbstractColleague. 
     */ 
    interface Filter 
    { 
 public function filter($value); 
    } 

    /** 
     * Colleague. We decide in the implementation phase 
     * that Colleagues should not know the next Colleague 
     * in the chain, resorting to a Mediator to link them together. 
     * This choice succesfully avoids a base abstract class 
     * for Filters. 
     * Remember that this is an example: it is not only 
     * Chain of Responsibility that can be alternatively implemented 
     * as a Mediator. 
     */ 
    class TrimFilter implements Filter 
    { 
  public function filter($value) 
  { 
      return trim($value); 
  } 
    }

    /**  <br>     * Colleague.  <br>     */  <br>    class NullFilter implements Filter  <br>    {  <br> public function filter($value)  <br> {  <br>     return $value ? $value : '';  <br> }  <br>    }  <br><br>    /**  <br>     * Colleague.  <br>     */  <br>    class HtmlEntitiesFilter implements Filter  <br>    {  <br> public function filter($value)  <br> {  <br>     return htmlentities($value);  <br> }  <br>    }<br>
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    /**  <br>     * The Mediator. We avoid referencing it from ConcreteColleagues  <br>     * and so the need for an interface. We leave the implementation  <br>     * of a bidirectional channel for the Observer pattern's example.  <br>     * This class responsibility is to store the value and coordinate  <br>     * filters computation when they have to be applied to the value.  <br>     * Filtering responsibilities are obviously a concern of  <br>     * the Colleagues, which are Filter implementations.  <br>     */  <br>    class InputElement  <br>    {  <br> protected $_filters;  <br> protected $_value;  <br><br> public function addFilter(Filter $filter)  <br> {  <br>     $this->_filters[] = $filter;  <br>     return $this;  <br> }  <br><br> public function setValue($value)  <br> {  <br>     $this->_value = $this->_filter($value);  <br> }  <br><br> protected function _filter($value)  <br> {  <br>     foreach ($this->_filters as $filter) {  <br>  $value = $filter->filter($value);  <br>     }  <br>     return $value;  <br> }  <br><br> public function getValue()  <br> {  <br>     return $this->_value;  <br> }    <br>    }  <br><br>    $input = new InputElement();  <br>    $input->addFilter(new NullFilter())  <br>   ->addFilter(new TrimFilter())  <br>   ->addFilter(new HtmlEntitiesFilter());  <br>    $input->setValue(' You should use the <h1>-<h6> tags for your headings.');  <br>    echo $input->getValue(), "\n";<br>
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