代理模式 & 装饰器模式 （Proxy & Decorator)

代理模式和装饰器模式虽然概念上区别很大，但是在实现时却又比较相似。

代理模式从概念上讲，就是我想访问一个服务，但是我却不需要知道真正给我提供服务的对象，我只要访问能提供给我服务的代理对象就可以了。

装饰器模式从概念上讲，就是要装饰一个对象，只要把这个对象通过装饰器的构造函数传入，装饰器会做一些额外的装饰。因为装饰器也实现了对象实现的接口，所以就可以像操作对象一样操作装饰器。

代理模式的类图：

Interface Subject:

 

package com.mode.interfaces
{
	public interface Subject
	{
	     function doAction():void;
	}
}

 RealSubject

 

package com.mode.concrete
{
	import com.mode.interfaces.Subject;
	
	public class RealSubject implements Subject
	{
		public function RealSubject()
		{
		}
		
		public function doAction():void
		{
			trace("Real Subject do Action");
		}
	}
}

 Proxy:

package com.mode.proxy
{
	import com.mode.concrete.RealSubject;
	import com.mode.interfaces.Subject;
	
	public class Proxy implements Subject
	{
		private var subject:Subject;		
		public function doAction():void
		{
			if(subject == null)
			{
				subject = new RealSubject();
			}
			doSomeActionBefore();
			subject.doAction();
			doSomeActionAfter();
			
		}
		
		private function doSomeActionBefore():void
		{
			trace("Proxy do some action before");
		}
		
		private function doSomeActionAfter():void
		{
			trace("Proxy do some action after");
		}
	}
}

 Client test:

<?xml version="1.0" encoding="utf-8"?>
<s:Application xmlns:fx="http://ns.adobe.com/mxml/2009" 
			   xmlns:s="library://ns.adobe.com/flex/spark" 
			   xmlns:mx="library://ns.adobe.com/flex/mx" minWidth="955" minHeight="600">
	<fx:Script>
		<![CDATA[
			import com.mode.interfaces.Subject;
			import com.mode.proxy.Proxy;
			protected function button1_clickHandler(event:MouseEvent):void
			{
				var subject:Subject = new com.mode.proxy.Proxy();
				subject.doAction();
				/* output: 
				Proxy do some action before
				Real Subject do Action
				Proxy do some action after 
				*/
			}
		]]>
	</fx:Script>
	<fx:Declarations>
		<!-- Place non-visual elements (e.g., services, value objects) here -->
	</fx:Declarations>
	<s:Button label="Proxy Demo" click="button1_clickHandler(event)"/>
</s:Application>

 你会发现我真正访问的是RealSubject的doAction，但是Proxy屏蔽了它并做了一些额外的服务。

Interface of Component:

package com.mode.interfaces
{
	public interface Component
	{
		function operation():void;
	}
}

 ConcreteComponent:

package com.mode.concrete
{
	import com.mode.interfaces.Component;
	
	public class ConcreteComponent implements Component
	{
		public function operation():void
		{
			trace("concreteComponent operation");
		}
	}
}

 Decorator:

package com.mode.concrete
{
	import com.mode.interfaces.Component;
	
	public class Decorator implements Component
	{
		protected var component:Component;
		public function Decorator(comp:Component)
		{
			component = comp;
		}
		
		public function operation():void
		{
			component.operation();
		}
	}
}

 ConcreteDecorator:

package com.mode.concrete
{
	import com.mode.interfaces.Component;
	
	public class ConcreteDecorator extends Decorator
	{
		private var additionalAttribute:String = "additional Attribute";
		public function ConcreteDecorator(comp:Component)
		{
			super(comp);
		}
		
		override public function operation():void
		{
			super.operation();
			addtionalBehavior();
		}
		private function addtionalBehavior():void
		{
			trace("Concrete decorator addtioanl behavior = " + additionalAttribute);
		}
	}
}

 APP test:

<?xml version="1.0" encoding="utf-8"?>
<s:Application xmlns:fx="http://ns.adobe.com/mxml/2009" 
			   xmlns:s="library://ns.adobe.com/flex/spark" 
			   xmlns:mx="library://ns.adobe.com/flex/mx" minWidth="955" minHeight="600">
	<fx:Script>
		<![CDATA[
			import com.mode.concrete.ConcreteComponent;
			import com.mode.concrete.ConcreteDecorator;
			import com.mode.concrete.Decorator;
			import com.mode.interfaces.Component;
			import com.mode.interfaces.Subject;
			import com.mode.proxy.Proxy;
			protected function button1_clickHandler(event:MouseEvent):void
			{
				var comp:Component = new ConcreteComponent();
				var decorator:Decorator = new ConcreteDecorator(comp);
				decorator.operation();
				/* output: 
				concreteComponent operation
				Concrete decorator addtioanl behavior = additional Attribute
				*/
			}
		]]>
	</fx:Script>
	<fx:Declarations>
		<!-- Place non-visual elements (e.g., services, value objects) here -->
	</fx:Declarations>
	<s:Button label="Decorator Demo" click="button1_clickHandler(event)"/>
</s:Application>

 你会发现是我把component传入了装饰器中，装饰器对component做了额外的装饰。

（******请注意装饰器和代理的初始化位置和方式*****）

装饰器模式应当为所装饰的对象提供增强功能，而代理模式对所代理对象的使用施加控制，并不提供对象本身的增强功能。

装饰器模式关注于在一个对象上动态的添加方法，然而代理模式关注于控制对对象的访问