我读设计模式之代理模式(Proxy Pattern)
引入 代理模式的使用非常广泛。开发过程中,有些对象是部署在网络中另外一台server上,比如web service。如果在客户端直接进行对象访问,会增加client操作的复杂度(处理网络通信的问题等)。这个时候,应用代理模式,在客户端建立远端对象的代理对象,让代理对象处理复杂的逻辑,而客户端只简单的调用此代理对象即可。
实际上,web service的使用就是这样:我们在客户端添加完对web service的引用后,就在本地生成了web service的代理,之后所有的操作,实际上就是对代理对象的操作。
例证(模拟web service服务)
1.UML
代理模式所涉及的角色有:
抽象主题角色(Subject):声明了真实主题和代理主题的共同接口,这样一来在任何使用真实主题的地方都可以使用代理主题。
代理主题(Proxy)角色:代理主题角色内部含有对真是主题的引用,从而可以在任何时候操作真实主题对象;代理主题角色提供一个与真实主题角色相同的接口,以便可以在任何时候都可以替代真实主体;控制真实主题的应用,负责在需要的时候创建真实主题对象(和删除真实主题对象);代理角色通常在将客户端调用传递给真实的主题之前或之后,都要执行某个操作,而不是单纯的将调用传递给真实主题对象。
真实主题角色(RealSubject)角色:定义了代理角色所代表的真实对象。
2.实现
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说明
1). 范例中代理类的实现只是对具体类的转发。但是实际应用中通常会在实际请求前后添加预请求和请求后的处理。
2).代理模式实现的要点很明确:代理类和被代理类要有统一的接口,这样才会有统一的实现,保证了代理的功能实现。
3).如果你希望降低对象的使用复杂度、或是提升对象使用的友好度、或是提高对象使用的效率都可以考虑代理模式。
总结
在软件系统中,增加一个中间层是我们解决问题的常见手法,这方面Proxy模式给了我们很好的实现。代理模式其实就是在访问对象的时候引入一定程度的间接性,因为这种间接性,我们可以附加更多的用途和控制。
学习参考:
http://www.cnblogs.com/Terrylee/archive/2006/05/18/403382.html
http://www.cnblogs.com/zhenyulu/articles/48128.aspx
http://www.cnblogs.com/lovecherry/archive/2007/10/08/917363.html
大话设计模式:代理模式