Symfony2中的设计模式——装饰者模式，symfony2设计模式

装饰者模式的定义

　　在不必改变原类文件和使用继承的情况下，动态地扩展一个对象的功能。它是通过创建一个包装对象，也就是装饰来包裹真实的对象。

　　装饰者模式把每个要装饰的功能放在单独的类中，并让这个类包装它要装饰的对象，因此，当需要执行特殊行为时，客户端代码就可以在运行的时候根据需要有选择地、按顺序地使用装饰功能包装对象了。

Symfony2中的设计模式——装饰者模式，symfony2设计模式_PHP教程图1

使用场景

　　设想一下，如果我们需要创建一个在不同场合有不同着装的学生，例如：在学校学生需要穿上校服，在舞会学生需要穿上正装，在家学生可以裸装（有点变态），当然，还可以学习超人把底裤穿在外面。这时候问题来了，难道我们要为每种场合编写一个不同穿着的学生类吗？如果我们的童鞋想要一个穿着校服裤子、正装上衣外露的底裤怎么办？StudentWithSchoolUniform、StudentWithFormalWear、StudentWithNaked、StudentWithSchoolUniformAndOutSideUnderWear..................绵绵无尽的类~~~累！是的，如果这样就造成类爆炸了，需求增加，类就不断的增加，整个系统的维护难度可想而知。

　　所以这时候，装饰者模式就可以发挥它的作用了，底裤、正装、校服、鞋子、眼镜等等都是具体的装饰者，学生是具体的被装饰的对象，被装饰的对象和装饰者的抽象类都继承者同一个父类。为学生穿上不同的服装，其实就是使用装饰者类（服装）包裹被装饰者类（学生），形象的说这是一个穿衣的过程。

类和接口

Component（被装饰对象基类，对应例子的Person类）
ConcreteComponent（具体被装饰对象，对应例子的Student类）
Decorator（装饰者基类，对应例子的Costume）
ContreteDecorator（具体的装饰者类，对应例子的Pants、Shirt等）

例子

图2

Person.php

Symfony2中的设计模式——装饰者模式，symfony2设计模式_PHP教程

1 php 2 3 /** 4 * Person.php 5 * 被装饰基类 6 **/ 7 abstract class Person{ 8 9 public abstract function show(); 10 11 } View Code

Student.php

1 php 2 3 /** 4 * Student.php 5 * 具体被装饰对象 6 **/ 7 class Student extends Person{ 8 9 private $name; 10 11 public function __construct($name){ 12 $this->name = $name; 13 } 14 15 public function show(){ 16 echo '我是学生',$this->name; 17 } 18 } View Code

Costume.php

1 php 2 3 /** 4 * Costume.php 5 * 装饰者基类 6 **/ 7 abstract class Costume extends Person{ 8 9 10 } View Code

Shirt.php

1 php 2 3 /** 4 * Shirt.php 5 * 具体的装饰者类 6 **/ 7 class Shirt extends Costume{ 8 9 private $person; 10 11 public function __construct(Person $person){ 12 13 $this->person = $person; 14 15 } 16 17 public function show(){ 18 19 echo $this->person->show(),',穿着衬衫'; 20 } 21 22 } View Code

Pants.php

1 php 2 3 /** 4 * Pants.php 5 **/ 6 class Pants extends Costume{ 7 8 private $person; 9 10 public function __construct(Person $person){ 11 12 $this->person = $person; 13 14 } 15 16 public function show(){ 17 18 echo $this->person->show(),',穿着裤子'; 19 } 20 21 } View Code

Glasses.php

1 php 2 3 /** 4 * Glasses.php 5 **/ 6 class Glasses extends Costume{ 7 8 private $person; 9 10 public function __construct(Person $person){ 11 12 $this->person = $person; 13 14 } 15 16 public function show(){ 17 18 echo $this->person->show(),',带着眼镜'; 19 } 20 21 } View Code

UnderWear.php

1 php 2 3 /** 4 * UnderWear.php 5 **/ 6 class UnderWear extends Costume{ 7 8 private $person; 9 10 public function __construct(Person $person){ 11 12 $this->person = $person; 13 14 } 15 16 public function show(){ 17 18 echo $this->person->show(),',穿着DK'; 19 } 20 21 } View Code

Client.php

<span> 1</span> <?<span>php
</span><span> 2</span> 
<span> 3</span>     <span>require_once</span> 'Person.php'<span>;
</span><span> 4</span>     <span>require_once</span> 'Costume.php'<span>;
</span><span> 5</span>     <span>require_once</span> 'Student.php'<span>;
</span><span> 6</span>     <span>require_once</span> 'UnderWear.php'<span>;
</span><span> 7</span>     <span>require_once</span> 'Shirt.php'<span>;
</span><span> 8</span>     <span>require_once</span> 'Pants.php'<span>;
</span><span> 9</span>     <span>require_once</span> 'Glasses.php'<span>;
</span><span>10</span> 
<span>11</span>     <span>//</span><span> Student继承Person</span>
<span>12</span>     <span>$jc</span> = <span>new</span> Student('JC'<span>);
</span><span>13</span>     <span>$jc</span>->show();   <span>//</span><span> 我是学生JC</span>
<span>14</span>     <span>echo</span> '<br>'<span>;
</span><span>15</span> 
<span>16</span>     <span>//</span><span> 用UnderWear类装饰Person</span>
<span>17</span>     <span>$underwear</span> = <span>new</span> UnderWear(<span>$jc</span><span>);
</span><span>18</span>     <span>$underwear</span>->show();  <span>//</span><span> 我是学生JC,穿着DK</span>
<span>19</span>     <span>echo</span> '<br>'<span>;
</span><span>20</span> 
<span>21</span>     <span>//</span><span> 再用Pants类装饰Person</span>
<span>22</span>     <span>$pants</span> = <span>new</span> Pants(<span>$underwear</span><span>);
</span><span>23</span>     <span>$pants</span>->show();   <span>//</span><span> 我是学生JC,穿着DK,穿着裤子</span>
<span>24</span>     <span>echo</span> '<br>'<span>;
</span><span>25</span> 
<span>26</span>     <span>//</span><span> 再用Shirt类装饰Person</span>
<span>27</span>     <span>$shirt</span> = <span>new</span> Shirt(<span>$pants</span><span>);
</span><span>28</span>     <span>$shirt</span>->show();  <span>//</span><span> 我是学生JC,穿着DK,穿着裤子,穿着衬衫</span>
<span>29</span>     <span>echo</span> '<br>'<span>;
</span><span>30</span> 
<span>31</span>     <span>//</span><span> 再用Glasses类装饰Person</span>
<span>32</span>     <span>$glasses</span> = <span>new</span> Glasses(<span>$shirt</span><span>);
</span><span>33</span>     <span>$glasses</span>->show();  <span>//</span><span> 我是学生JC,穿着DK,穿着裤子,穿着衬衫,带着眼镜</span>
<span>34</span>     <span>echo</span> '<br>';

登录后复制

Symfony2中的设计模式——装饰者模式，symfony2设计模式_PHP教程图3 输出结果截图

Symfony2 EventDispatch 组件对装饰者模式的应用

Symfony2中的设计模式——装饰者模式，symfony2设计模式_PHP教程图4 Symfony2 EventDispatch组件使用装饰模式

图5 Framework配置EventDispatcher

Symfony\Component\EventDispatcher\EventDispatcherInterface 是被装饰的接口
Symfony\Component\EventDispatcher\EventDispatcher 和 Symfony\Component\EventDispatcher\ContainerAwareEventDispatcher 是被装饰的具体对象
Symfony\Component\EventDispatcher\Debug\TraceableEventDispatcherInterface 装饰者接口
Symfony\Component\EventDispatcher\Debug\TraceableEventDispatcher 装饰者基类
Symfony\Component\HttpKernel\Debug\TraceableEventDispatcher 具体的装饰者对象

　　具体装饰者对象Symfony\Component\HttpKernel\Debug\TraceableEventDispatcher::dispatch()方法，核心依旧是调用被装饰的具体对象Symfony\Component\EventDispatcher\EventDispatcher::dispatch()方法进行工作，但是装饰者对象Symfony\Component\HttpKernel\Debug\TraceableEventDispatcher::dispatch()方法添加了相应的功能，例如在调用Symfony\Component\EventDispatcher\EventDispatcher::dispatch()方法前后分别调用了preProcess()、preDispatch()和postDispatch()、postProcess():

<span> 1</span>     <span>/*</span><span>*
</span><span> 2</span> <span>     * {@inheritdoc}
</span><span> 3</span>      <span>*/</span>
<span> 4</span>     <span>public</span> <span>function</span> dispatch(<span>$eventName</span>, Event <span>$event</span> = <span>null</span><span>)
</span><span> 5</span> <span>    {
</span><span> 6</span>         <span>if</span> (<span>null</span> === <span>$event</span><span>) {
</span><span> 7</span>             <span>$event</span> = <span>new</span><span> Event();
</span><span> 8</span> <span>        }
</span><span> 9</span> 
<span>10</span>         <span>//</span><span> 装饰者对象增加的功能</span>
<span>11</span>         <span>$this</span>->preProcess(<span>$eventName</span><span>);
</span><span>12</span>         <span>$this</span>->preDispatch(<span>$eventName</span>, <span>$event</span><span>);
</span><span>13</span> 
<span>14</span>         <span>$e</span> = <span>$this</span>->stopwatch->start(<span>$eventName</span>, 'section'<span>);
</span><span>15</span> 
<span>16</span>         <span>//</span><span> 核心依旧是调用被装饰的具体对象Symfony\Component\EventDispatcher\EventDispatcher::dispatch()方法</span>
<span>17</span>         <span>$this</span>->dispatcher->dispatch(<span>$eventName</span>, <span>$event</span><span>);
</span><span>18</span> 
<span>19</span>         <span>if</span> (<span>$e</span>-><span>isStarted()) {
</span><span>20</span>             <span>$e</span>-><span>stop();
</span><span>21</span> <span>        }
</span><span>22</span> 
<span>23</span>         <span>//</span><span> 装饰者对象增加的功能</span>
<span>24</span>         <span>$this</span>->postDispatch(<span>$eventName</span>, <span>$event</span><span>);
</span><span>25</span>         <span>$this</span>->postProcess(<span>$eventName</span><span>);
</span><span>26</span> 
<span>27</span>         <span>return</span> <span>$event</span><span>;
</span><span>28</span>     }

登录后复制

优点

缺点