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<h3 align="center">设计模式之Chain of Responsibility(职责链)</h3>
<p align="center"><a href="http://www.jdon.com/aboutme.htm">板桥里人</a> http://www.jdon.com
2002/04/21(转载请保留)</p>
<p align="center"><a href="../mybook/index.htm" target="_blank"><strong>模式实战书籍《Java实用系统开发指南》</strong></a></p>
<p><b>Chain of Responsibility定义</b><br>
Chain of Responsibility(CoR) 是用一系列类(classes)试图处理一个请求request,这些类之间是一个松散的耦合,唯一共同点是在他们之间传递request.
也就是说,来了一个请求,A类先处理,如果没有处理,就传递到B类处理,如果没有处理,就传递到C类处理,就这样象一个链条(chain)一样传递下去。</p>
<p><b>如何使用?</b><br>
虽然这一段是如何使用CoR,但是也是演示什么是CoR.</p>
<p>有一个Handler接口:</p>
<p>public interface Handler{<br>
public void handleRequest();<br>
}</p>
<p>这是一个处理request的事例, 如果有多种request,比如 请求帮助 请求打印 或请求格式化:<br>
<br>
最先想到的解决方案是:在接口中增加多个请求:<br>
public interface Handler{<br>
public void handleHelp();<br>
public void handlePrint();<br>
public void handleFormat();</p>
<p>}</p>
<p>具体是一段实现接口Handler代码:<br>
public class ConcreteHandler implements Handler{<br>
private Handler successor;</p>
<p> public ConcreteHandler(Handler successor){<br>
this.successor=successor;<br>
}</p>
<p> public void handleHelp(){<br>
//具体处理请求Help的代码<br>
...<br>
}</p>
<p> public void handlePrint(){<br>
//如果是print 转去处理Print<br>
successor.handlePrint();<br>
}<br>
public void handleFormat(){<br>
//如果是Format 转去处理format<br>
successor.handleFormat();<br>
}</p>
<p>}<br>
一共有三个这样的具体实现类,上面是处理help,还有处理Print 处理Format这大概是我们最常用的编程思路。</p>
<p>虽然思路简单明了,但是有一个扩展问题,如果我们需要再增加一个请求request种类,需要修改接口及其每一个实现。</p>
<p>第二方案:将每种request都变成一个接口,因此我们有以下代码 :</p>
<p>public interface HelpHandler{<br>
public void handleHelp();<br>
}</p>
<p>public interface PrintHandler{<br>
public void handlePrint();<br>
}</p>
<p>public interface FormatHandler{<br>
public void handleFormat();<br>
}</p>
<p>public class ConcreteHandler<br>
implements HelpHandler,PrintHandler,FormatHandlet{<br>
private HelpHandler helpSuccessor;<br>
private PrintHandler printSuccessor;<br>
private FormatHandler formatSuccessor;</p>
<p> public ConcreteHandler(HelpHandler helpSuccessor,PrintHandler printSuccessor,FormatHandler
formatSuccessor)<br>
{<br>
this.helpSuccessor=helpSuccessor;<br>
this.printSuccessor=printSuccessor;<br>
this.formatSuccessor=formatSuccessor;<br>
}</p>
<p> public void handleHelp(){<br>
.......<br>
}</p>
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