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Delegation pattern example tutorial in php

Jul 01, 2017 pm 01:29 PM
phpExampleTutorial

委托模式是软件设计模式中的一项基本技巧。在委托模式中,有两个对象参与处理同一个请求,接受请求的对象将请求委托给另一个对象来处理。委托模式是一项基本技巧,许多其他的模式,如状态模式策略模式访问者模式本质上是在更特殊的场合采用了委托模式。

动态委托的介绍:动态委托概念来自于Jakarta 字节码工程库 (Byte-Code Engineering Library, BCEL)。它能够分析存在的类,并且对于接口,抽象类,甚至运行时的具体类来说,它能够生成以字节编码委托类。
被委托的接口/类应该满足如下条件:动态委托最多只能委托一个类,但是能够代理多个接口。这个限制来自于Java的单继承模式。一个Java类最多只有一个父类。既然生成的委托类把被委托类作为它的父类,那么指定多个被委托类是不合理的。如果没有指定被委托类,那么缺省的父类就是Object。
下面是PHP 反射机制实现动态代理的代码:

<?php
class Fruit

{

  function callFruit()

  {
    print "Generate an Apple";
  }

}

class FruitDelegator
{
 private $targets;
  function construct()
  {
    $this->target[] = new Fruit();
  }
  
  function call($name, $args)

  {
    foreach ($this->target as $obj)
    {
      $r = new ReflectionClass($obj);
      if ($method = $r->getMethod($name))

      {

        if ($method->isPublic() && !$method->isAbstract())
        {

          return $method->invoke($obj, $args);
        }

      }

    }
  }

}

$obj = new FruitDelegator();

$obj->callFruit();

// 运行结果

// Generate an Apple
?>

可见,通过代理类FruitDelegator来代替Fruit类来实现他的方法。
同样的,如下的代码也是能够运行的:

<?php
class Color

{
  function callColor()
  {
    print "Generate Red";
  }
}
 

class ColorDelegator

{

  private $targets;

   

  function addObject($obj)

  {

    $this->target[] = $obj;

  }

   

  function call($name, $args)

  {

    foreach ($this->target as $obj)

    {

      $r = new ReflectionClass($obj);

      if ($method = $r->getMethod($name))

      {

        if ($method->isPublic() && !$method->isAbstract())

        {
          return $method->invoke($obj, $args);
        }
      }
    }
  }
}

$obj = new ColorDelegator();
$obj->addObject(new Color());
$obj->callColor();

?>

设计了一个cd类,类中有mp3播放模式,和mp4播放模式
改进前,使用cd类的播放模式,需要在实例化的类中去判断选择什么方式的播放模式
改进后,播放模式当做一个参数传入playList函数中,就自动能找到对应需要播放的方法。

一、未改进前

<?php 
//使用委托模式之前,调用cd类,选择cd播放模式是复杂的选择过程 
class cd { 
 protected $cdInfo = array(); 
  
 public function addSong($song) { 
  $this->cdInfo[$song] = $song; 
 } 
  
 public function playMp3($song) { 
  return $this->cdInfo[$song] . &#39;.mp3&#39;; 
 } 
  
 public function playMp4($song) { 
  return $this->cdInfo[$song] . &#39;.mp4&#39;; 
 } 
} 
$oldCd = new cd; 
$oldCd->addSong("1"); 
$oldCd->addSong("2"); 
$oldCd->addSong("3"); 
$type = &#39;mp3&#39;; 
if ($type == &#39;mp3&#39;) { 
 $oldCd->playMp3(); 
} else { 
 $oldCd->playMp4(); 
}

二、通过委托模式,改进后的cd类

<?php
 
namespace Tools;
 
/*
委托模式
去除核心对象中的判决和复杂功能性
*/
 
//委托接口
interface Delegate{
 public function playList($list,$song);
}
 
//mp3处理类
class mp3 implements Delegate{
 public function playList($list,$song){
  return $list[$song].&#39;.mp3&#39;;
 }
}
 
//mp4处理类
class mp4 implements Delegate{
 public function playList($list, $song)
 {
  return $list[$song].&#39;.mp4&#39;;
 }
}
 
class cdDelegate{
 protected $cdInfo = array();
 
 public function addSong($song){
  $this->cdInfo[$song] = $song;
 }
 
 public function play($type,$song){
  $name = &#39;\Tools\\&#39;.$type;
  $obj = new $name;
  return $obj->playList($this->cdInfo,$song);
 }
}
 
$newCd = new cdDelegate();
$newCd->addSong("1");
$newCd->addSong("2");
$newCd->addSong("3");
echo $newCd->play(&#39;mp3&#39;,&#39;1&#39;);//只要传递参数就能知道需要选择何种播放模式

再为大家分享一个实例:

<?php
/**
 * 委托模式 示例
 */
class PlayList
{
 var $_songs = array();
 var $_object = null;
 
 function PlayList($type)
 {
  $object = $type."PlayListDelegation";
  $this->_object = new $object();
 }
 
 function addSong($location,$title)
 {
  $this->_songs[] = array("location"=>$location,"title"=>$title);
 }
 
 function getPlayList()
 {
  return $this->_object->getPlayList($this->_songs);
 }
}
 
class mp3PlayListDelegation
{
 function getPlayList($songs)
 {
  $aResult = array();
  foreach($songs as $key=>$item)
  {
   $path = pathinfo($item[&#39;location&#39;]);
   if(strtolower($item[&#39;extension&#39;]) == "mp3")
   {
    $aResult[] = $item;
   }
  }
  return $aResult;
 }
}
 
class rmvbPlayListDelegation
{
 function getPlayList($songs)
 {
  $aResult = array();
  foreach($songs as $key=>$item)
  {
   $path = pathinfo($item[&#39;location&#39;]);
   if(strtolower($item[&#39;extension&#39;]) == "rmvb")
   {
    $aResult[] = $item;
   }
  }
  return $aResult;
 }
}
 
$oMP3PlayList = new PlayList("mp3");
$oMP3PlayList->getPlayList();
$oRMVBPlayList = new PlayList("rmvb");
$oRMVBPlayList->getPlayList();
?>

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