门面模式(Façade Pattern)

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FaMILY: 宋体; mso-bidi-font-size: 12.0pt; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">模式产生的背景

1FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">、沉重的网络负担

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">在没有SessionBeanFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">的时候，客户端直接同底层的EntityBeanFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">进行交互，形成的是一种具有紧密耦合的硬编码机制，对于远程的客户来说，还附加了沉重的网络交互负担，具体的交互图如下：

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">在上面的图中，我们假设客户是通过网络对EntityBeanFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">的访问，如果EntityBeanFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">中有4FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">个字段ABCDFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">，客户要进行字段ABCDFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">的值的设置，就要进行4FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">次网络的传输，我们知道，一个客户要远程与EntityBeanFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">交互，就要经过如下的操作：

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">这样一来，每次进行一次字段ABCDFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">的设定，都要经过4FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">次网络交互，网络的速度一直就是分布式的一个瓶颈，如此沉重的负担毫无疑问会成为项目的拦路虎。

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">期待的解决方案：FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">如果一次把信息通过网络传输过去，4FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">个字段的设置都在本地服务中进行，就会较少75%FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">的网络负担。

2FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">、严重的不一致错误

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">我们再看看上面的这个模型，上面的模型有时候（概率也许非常小）会导致数据的不一致，例如，我们设置了字段ABFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">，当设置字段CFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">的时候，网络突然中断了，怎么办？

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">网络中断就意味着客户虽然设置了ABFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">，却没有办法设置CDFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">，如果CDFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">和ABFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">是相关联的，例如AFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">代表账号，BFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">代表用户名，CFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">代表存款余额，DFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">代表日期，当账号和用户名都改了，本来存款和日期也应该一并修改，但是网络的中断破坏了数据的这种一致性，这无论对用户还是对银行都是一种威胁。

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">期待的解决方案：FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">如果网络出现异常后，远程服务器能够进行数据的rollbackFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">，那么这种危险的不一致问题就有可能得到解决。

3FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">、硬编码导致的高耦合

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">我们再回头看看上面的模型，我们会发现，如果EntityBeanFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">由于某种原因需要改动，那么客户端的代码也必须进行修改，因为客户端是对EntityBeanAPIFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">的硬编码，同时我们也很清楚，客户的需求是多变的，这种高耦合会使我们的项目很快破产。

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">期待的解决方案：FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">如果能够做到层次的分离，就如同数据库中的外模式、模式、内模式一样，那么就可以克服高耦合，提高系统的健壮性和灵活性。

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">当然，在实际的应用中，还可能会有这样那样的问题，但是上面的这3FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">个问题就足以促使我们去使用FaçadeFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">模式。

FaçadeFaMILY: 宋体; mso-bidi-font-size: 12.0pt; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">模式的框架结构

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">在使用FaçadeFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">模式之前，我们先来看一下什么是FaçadeFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">模式FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">（中文名：门面模式、外观模式）。

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">我们先举一个现实中的例子：新生报道。我们都有过去学校作为新生报道的经历，我们先接到通知，然后坐火车/FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">汽车/FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">自行车，到大学校门口，找新生报道的地点，交上资料，在新生接待处登记，然后去交费处领取交费表单，填写后交费，拿着交费单据去核实处盖章，拿着这些收据返回新生接待处，然后……

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">这里我们可以看到，新生要和下面的这些人打交道：

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">售票员FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">：买火车票/FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">汽车票（如果你骑自行车/FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">走路，这一步可以省略：）

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">新生接待员FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">：你要报道，自然就要找他。

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">收费人员FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">：你的学费、住宿费就是通过他向“万恶”的学校提交。

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">核实人员FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">：你还要向他领取收据。

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">其实，我们知道真正报道的时候，总会有一些意想不到的问题，这些都要我们自己去解决，如果你没有一点经验，恐怕其中还会有一些挫折：）

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">面向如此繁琐的事情，我们总是觉得不爽，如果我们不去和他们打交道，有专门的人员帮我们负责这些事情，那是再好不过的了，赫赫，这个不用担心了，聪明的父母早就想好了：送小孩子去！

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">如今的问题变得简单多了，你只要和你父母打交道，即便你对外界了解得不多也不会有什么障碍----FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">有父母呢，怕什么？：）

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">在这里，我们不知不觉的用到了FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">一个法则：Law Of DemeterFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">（中文名：迪米特法则）FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">，FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">一个模式：FaçadeFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">。

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">迪米特法则最初是由Han Holland1987FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">年在美国Northeastern UniversityFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">做一个名为DemeterFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">的项目时提出来的，这个法则有以下几个表达方式：

1、FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">只和你的朋友们通信。我们上面的例子就是只和父母通信。

2、FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">不要和陌生人讲话。有父母在我们身边，还有必要和陌生人讲话么？除非你这个人特爱交朋友，那样的话算我一个：）

3、FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">每一个软件单位对其他的单位都只有最少的知识，而且仅局限于那些与本单位密切相关的软件单位。嗯，这个作为一个“两耳不闻窗外事，一心只读圣贤书”的学生，恐怕再适合不过了（指的是我们那时候的高中生，现在的高中生，哎….FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">）

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">聪明的您一定看出来了，我们举的例子对这个原则是在适合不过了。其实，

FaçadeFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">模式只不过是这个原则的一个应用罢了，我们来看一下FaçadeFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">模式的结构图：

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">我们从上面的图中可以清楚的看到，没有采用FaçadeFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">模式的系统极其复杂，元素之间的沟通非常困难，因为你要对周围的元素非常了解，换句话说，你要有足够的知识和经验（但是在如今的软件开发中，知识更新如此迅速，要做到这一点很难，不过网络承担起了FaçadeFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">的作用）。采用了FaçadeFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">模式的系统看起来非常的整洁和清爽，元素不需要对其他的元素有非常的了解，只要对FaçadeFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">元素了解即可，其他的任务就有FaçadeFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">一人去做吧。

FaçadeFaMILY: 宋体; mso-bidi-font-size: 12.0pt; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">模式的优点和缺点

FaMILY: 宋体; mso-bidi-font-size: 12.0pt; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">按照惯例，我们先说优点，再说缺点：

1、SessionBeanFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">的产生，较少了网络负载。

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">对于最初的模型，我们可以改进如下：

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">这样，我们在客户层和EntityBeanFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">层，放置了一个中间层FaçadeFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">，FaçadeFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">就是这里的SessionBeanFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">，SessionBeanFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">可以和EntityBeanFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">运行在同一个JVMFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">上的相同的容器中，如此一来，SessionBeanFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">就可以借助EntityBeanFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">的本地接口，屏蔽掉耗资巨大的远程调用，实现高效处理。客户只需要远程访问一次FaçadeFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">，就可以完成4FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">个字段的设置工作。

1、SessionBeanFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">把一致性工作进行了转接。

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">在上面我们提到了，在没有FaçadeFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">情况下，网络如果发生错误，就有可能导

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">致数据的不一致。这个问题产生的根源就在于EntityBeanFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">只是负责数据逻辑（Data logicFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">），对于业务逻辑一无所知，自然也就没有办法进行回滚。

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">我们加上了一个Façade---SessionBeanFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">，就是来负责业务逻辑，SessionBeanFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">很清楚那些情况应该加锁，哪些情况应该回滚，把这些操作当作一个事务，然后把事务的处理工作通过描述符告诉容器去控制。

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">如此一来既保证了ACIDFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">，又减轻了程序员的工作，并且把业务逻辑与数据逻辑分开，是开发流程更加的清晰，工程进度自然加快。

2、SessionBeanFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">以修改为己任

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">如果没有FaçadeFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">，客户代码不得不硬编码进EntityBeanFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">，如果EntityBean

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">发生了修改，哪怕就只是一点点，客户端恐怕就要大动干戈。对此，作为开发者显然不能够接受，只有遵循“开闭原则”，才能够满足要求。换句话说，你不是想修改么，没问题，不过条件有一个：你改你的代码，但是不要影响到我。

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">怎么样才能够做到不影响客户的代码呢？加一个中间层，这个位置正好有SessionBeanFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">来顶替，SessionBeanFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">提供的是一个业务接口，处理业务逻辑，EntityBeanFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">的改变只会影响到和他紧密联系的SessionBeanFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">，“Trouble stops hereFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">”

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">这就是SessionBeanFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">的至理名言虽然业务逻辑内部有所变动，但他不会反映到接口上来，这也算是ISPFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">的一个应用吧。

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">接口和实现的分离，降低了系统与客户的耦合性，使得层次结构更为突出，消除了令人头疼的循环依赖。

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">这还有一个好处就是可移植性增强，由于与客户代码的分离，使得模块化程度增高，独立性增强，可移植性也随之增加。

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">缺点：

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">虽然SessionBeanFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">又如此众多的优点，但是也有一个致命的缺点：不符合开闭原则。所谓的开闭原则是软件工程里面一个最基本的原则：对扩展开放，对修改关闭。换句话说，你的系统可以提供新的功能模块而不必进行修改。

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">由于SessionBeanFaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">与客户端直接交互，客户端的代码势必要硬编码进业务逻辑，如此一来，一旦业务逻辑模块发生变动（增加/FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'">删除）势必带来客户端代码的中断。

FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'; mso-font-kerning: 1.0pt; mso-bidi-font-Family: 'Times New Roman'; mso-ansi-language: EN-US; mso-Fareast-language: ZH-CN; mso-bidi-language: AR-SA">期待的解决方案：FaMILY: 宋体; mso-ascii-font-Family: 'Times New Roman'; mso-hansi-font-Family: 'Times New Roman'; mso-font-kerning: 1.0pt; mso-bidi-font-Family: 'Times New Roman'; mso-ansi-language: EN-US; mso-Fareast-language: ZH-CN; mso-bidi-language: AR-SA">独立于客户端，真正达到“热拔插”。

门面模式(Fa&ccedil;ade Pattern)

门面模式(Façade Pattern)