设计模式—— 十六 ：责任链模式

于 2025-06-27 17:30:25 发布
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分类专栏： 程序员 Java 文章标签： 设计模式 责任链模式
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什么是责任链模式？

职责链模式的定义：

Avoid coupling the sender of a request to its receiver by giving more than one object a chance to handle the request.Chain the receiving objects and pass the request along the chain until an object handles it.（使多个对象都有机会处理请求，从而避免了请求的发送者和接受者之间的耦合关 系。将这些对象连成一条链，并沿着这条链传递该请求，直到有对象处理它为止。）

责任链模式的重点是在“链”上，由一条链去处理相似的请求在链中决定谁来处理这个请求，并返回相应的结果，

通用类图如图16-1所示:

图16-1:命令模式模式通用类图

在这里插入图片描述

责任链模式的核心在“链”上，“链”是由多个处理者ConcreteHandler组成的，包含如下几个角色：

● Handler（抽象处理者）：

 抽象处理者实现三个职责：

  • 一是定义一个请求的处理方法handleMessage，唯一对外开放的方法；
  • 二是定义一个链的编排方法setNext，设置下一个处理者；
  • 三是定义了具体的请求者必须实现的两个方法：定义自己能够处理的级别getHandlerLevel和具体的处理任务echo。
复制代码 
<span style="color:#141418"><span style="background-color:#ffffff"><code class="language-java"><span style="color:#a626a4">public</span> <span style="color:#a626a4">abstract</span> <span style="color:#a626a4">class</span> <span style="color:#4078f2">Handler</span> {
	<span style="color:#a626a4">private</span> Handler nextHandler; <span style="color:#a0a1a7"><em>// 每个处理者都必须对请求做出处理</em></span>

	<span style="color:#a626a4">public</span> <span style="color:#a626a4">final</span> Response <span style="color:#4078f2">handleMessage</span>(Request request) {
		<span style="color:#986801">Response</span> <span style="color:#986801">response</span> <span style="color:#ab5656">=</span> <span style="color:#0184bb">null</span>;
		<span style="color:#a0a1a7"><em>// 判断是否是自己的处理级别</em></span>
		<span style="color:#a626a4">if</span> (<span style="color:#c18401">this</span>.getHandlerLevel().equals(request.getRequestLevel())) {
			response = <span style="color:#c18401">this</span>.echo(request);
		} <span style="color:#a626a4">else</span> { <span style="color:#a0a1a7"><em>// 不属于自己的处理级别</em></span>
					<span style="color:#a0a1a7"><em>// 判断是否有下一个处理者</em></span>
			<span style="color:#a626a4">if</span> (<span style="color:#c18401">this</span>.nextHandler != <span style="color:#0184bb">null</span>) {
				response = <span style="color:#c18401">this</span>.nextHandler.handleMessage(request);
			} <span style="color:#a626a4">else</span> {
				<span style="color:#a0a1a7"><em>// 没有适当的处理者，业务自行处理</em></span>
			}
		}
		<span style="color:#a626a4">return</span> response;
	}

	<span style="color:#a0a1a7"><em>// 设置下一个处理者是谁</em></span>
	<span style="color:#a626a4">public</span> <span style="color:#a626a4">void</span> <span style="color:#4078f2">setNext</span>(Handler _handler) {
		<span style="color:#c18401">this</span>.nextHandler = _handler;
	}

	<span style="color:#a0a1a7"><em>// 每个处理者都有一个处理级别</em></span>
	<span style="color:#a626a4">protected</span> <span style="color:#a626a4">abstract</span> Level <span style="color:#4078f2">getHandlerLevel</span>();

	<span style="color:#a0a1a7"><em>// 每个处理者都必须实现处理任务</em></span>
	<span style="color:#a626a4">protected</span> <span style="color:#a626a4">abstract</span> Response <span style="color:#4078f2">echo</span>(Request request);
}
</code></span></span>

在处理者中涉及三个类：Level类负责定义请求和处理级别，Request类负责封装请 求，Response负责封装链中返回的结果，该三个类都需要根据业务产生，可以在实际应用中完成相关的业务填充:

复制代码 
<span style="color:#141418"><span style="background-color:#ffffff"><code class="language-java"><span style="color:#a626a4">public</span> <span style="color:#a626a4">class</span> <span style="color:#4078f2">Level</span> {
	<span style="color:#a0a1a7"><em>//定义一个请求和处理等级</em></span>
}

<span style="color:#a626a4">public</span> <span style="color:#a626a4">class</span> <span style="color:#4078f2">Request</span> {
	<span style="color:#a0a1a7"><em>//请求的等级 </em></span>
	<span style="color:#a626a4">public</span> Level <span style="color:#4078f2">getRequestLevel</span>(){ <span style="color:#a626a4">return</span> <span style="color:#0184bb">null</span>; }
}

<span style="color:#a626a4">public</span> <span style="color:#a626a4">class</span> <span style="color:#4078f2">Response</span> {
	<span style="color:#a0a1a7"><em>//处理者返回的数据</em></span>
}
</code></span></span>

● ConcreteHandler（具体处理者）:

复制代码 
<span style="color:#141418"><span style="background-color:#ffffff"><code class="language-java"><span style="color:#a626a4">public</span> <span style="color:#a626a4">class</span> <span style="color:#4078f2">ConcreteHandler1</span> <span style="color:#a626a4">extends</span> <span style="color:#4078f2">Handler</span>{

	<span style="color:#a0a1a7"><em>/**
	 * 设置自己的处理级别
	 */</em></span>
	<span style="color:#4078f2">@Override</span>
	<span style="color:#a626a4">protected</span> Level <span style="color:#4078f2">getHandlerLevel</span>() {
		<span style="color:#a0a1a7"><em>// TODO Auto-generated method stub</em></span>
		<span style="color:#a626a4">return</span> <span style="color:#0184bb">null</span>;
	}

	<span style="color:#a0a1a7"><em>/**
	 * 定义自己的处理逻辑
	 */</em></span>
	<span style="color:#4078f2">@Override</span>
	<span style="color:#a626a4">protected</span> Response <span style="color:#4078f2">echo</span>(Request request) {
		<span style="color:#a0a1a7"><em>// TODO Auto-generated method stub</em></span>
		<span style="color:#a626a4">return</span> <span style="color:#0184bb">null</span>;
	}

}
</code></span></span>

定义了三个处理者，代码都是一样，此处不重复贴出。

● Client（客户端）：在客户端或高层模块中对链进行组装，并传递请求，返回结果。

复制代码 
<span style="color:#141418"><span style="background-color:#ffffff"><code class="language-java"><span style="color:#a626a4">public</span> <span style="color:#a626a4">class</span> <span style="color:#4078f2">Client</span> {

	<span style="color:#a0a1a7"><em>/**
	 * <span style="color:#a626a4">@param</span> args
	 */</em></span>
	<span style="color:#a626a4">public</span> <span style="color:#a626a4">static</span> <span style="color:#a626a4">void</span> <span style="color:#4078f2">main</span>(String[] args) {
		<span style="color:#a0a1a7"><em>//声明所有的处理节点</em></span>
		<span style="color:#986801">Handler</span> <span style="color:#986801">handler1</span> <span style="color:#ab5656">=</span> <span style="color:#a626a4">new</span> <span style="color:#4078f2">ConcreteHandler1</span>(); 
		<span style="color:#986801">Handler</span> <span style="color:#986801">handler2</span> <span style="color:#ab5656">=</span> <span style="color:#a626a4">new</span> <span style="color:#4078f2">ConcreteHandler2</span>(); 
		<span style="color:#986801">Handler</span> <span style="color:#986801">handler3</span> <span style="color:#ab5656">=</span> <span style="color:#a626a4">new</span> <span style="color:#4078f2">ConcreteHandler3</span>(); 
		<span style="color:#a0a1a7"><em>//设置链中的阶段顺序1-->2-->3 </em></span>
		handler1.setNext(handler2); 
		handler2.setNext(handler3); 
		<span style="color:#a0a1a7"><em>//提交请求，返回结果 </em></span>
		<span style="color:#986801">Response</span> <span style="color:#986801">response</span> <span style="color:#ab5656">=</span> handler1.handleMessage(<span style="color:#a626a4">new</span> <span style="color:#4078f2">Request</span>());
	}

}
</code></span></span>

在实际应用中，一般会有一个封装类对责任模式进行封装，也就是替代Client类，直接返回链中的第一个处理者，具体链的设置不需要高层次模块关系，这样，更简化了高层次模 块的调用，减少模块间的耦合，提高系统的灵活性。

为什么要用责任链模式

这里有一个业务场景，在万恶的封建社会，女子讲究“三从四德”，“三从”是指“未嫁从父、既嫁从夫、夫死从子”。

不使用责任链模式

以批判的态度去分析这个业务场景，类图如下：

图16-2:腐朽的“三从”类图

在这里插入图片描述
IHandler是三个有决策权对象的接口，IWomen是女性的代码。下面是实现：

  • IWomen（妇女接口）：
复制代码 
<span style="color:#141418"><span style="background-color:#ffffff"><code class="language-java"><span style="color:#a626a4">public</span> <span style="color:#a626a4">interface</span> <span style="color:#4078f2">IWomen</span> {
	<span style="color:#a0a1a7"><em>//获得个人状况 </em></span>
	<span style="color:#a626a4">public</span> <span style="color:#986801">int</span> <span style="color:#4078f2">getType</span>(); 
	<span style="color:#a0a1a7"><em>//获得个人请示 </em></span>
	<span style="color:#a626a4">public</span> String <span style="color:#4078f2">getRequest</span>();
}
</code></span></span>
  • Women（妇女实现类）：
复制代码 
<span style="color:#141418"><span style="background-color:#ffffff"><code class="language-java"><span style="color:#a626a4">public</span> <span style="color:#a626a4">class</span> <span style="color:#4078f2">Women</span> <span style="color:#a626a4">implements</span> <span style="color:#4078f2">IWomen</span>{
	<span style="color:#a0a1a7"><em>/** 通过一个int类型的参数来描述妇女的个人状况 * 1--未出嫁 * 2--出嫁 * 3--夫死 */</em></span>
	<span style="color:#a626a4">private</span> <span style="color:#986801">int</span> <span style="color:#986801">type</span> <span style="color:#ab5656">=</span> <span style="color:#986801">0</span>;
	<span style="color:#a0a1a7"><em>// 妇女的请示</em></span>
	<span style="color:#a626a4">private</span> <span style="color:#986801">String</span> <span style="color:#986801">request</span> <span style="color:#ab5656">=</span> <span style="color:#50a14f">""</span>;

	<span style="color:#a0a1a7"><em>// 构造函数传递过来请求</em></span>
	<span style="color:#a626a4">public</span> <span style="color:#4078f2">Women</span>(<span style="color:#986801">int</span> _type, String _request) {
		<span style="color:#c18401">this</span>.type = _type;
		<span style="color:#c18401">this</span>.request = _request;
	}

	<span style="color:#a0a1a7"><em>// 获得自己的状况</em></span>
	<span style="color:#a626a4">public</span> <span style="color:#986801">int</span> <span style="color:#4078f2">getType</span>() {
		<span style="color:#a626a4">return</span> <span style="color:#c18401">this</span>.type;
	}

	<span style="color:#a0a1a7"><em>// 获得妇女的请求</em></span>
	<span style="color:#a626a4">public</span> String <span style="color:#4078f2">getRequest</span>() {
		<span style="color:#a626a4">return</span> <span style="color:#c18401">this</span>.request;
	}
}
</code></span></span>
  • IHandler（有处理权的人员接口）：
复制代码 
<span style="color:#141418"><span style="background-color:#ffffff"><code class="language-java"><span style="color:#a626a4">public</span> <span style="color:#a626a4">interface</span> <span style="color:#4078f2">IHandler</span> {
	<span style="color:#a0a1a7"><em>//一个女性（女儿、妻子或者母亲）要求逛街，你要处理这个请求 </em></span>
	<span style="color:#a626a4">public</span> <span style="color:#a626a4">void</span> <span style="color:#4078f2">HandleMessage</span>(IWomen women);
}
</code></span></span>
  • 实现类：有处理权的人对妇女的请求进行处理，分别有三个实现类，在女儿没有出嫁之前父亲是有决定权的；在女性出嫁后，丈夫有决定权；在女性丧偶后，对母亲提出的请求儿子有决定权；
复制代码 
<span style="color:#141418"><span style="background-color:#ffffff"><code class="language-java"><span style="color:#a626a4">public</span> <span style="color:#a626a4">class</span> <span style="color:#4078f2">Father</span> <span style="color:#a626a4">implements</span> <span style="color:#4078f2">IHandler</span> {
	<span style="color:#a0a1a7"><em>// 未出嫁的女儿来请示父亲</em></span>
	<span style="color:#a626a4">public</span> <span style="color:#a626a4">void</span> <span style="color:#4078f2">HandleMessage</span>(IWomen women) {
		System.out.println(<span style="color:#50a14f">"女儿的请示是："</span> + women.getRequest());
		System.out.println(<span style="color:#50a14f">"父亲的答复是:同意"</span>);
	}
}

<span style="color:#a626a4">public</span> <span style="color:#a626a4">class</span> <span style="color:#4078f2">Husband</span> <span style="color:#a626a4">implements</span> <span style="color:#4078f2">IHandler</span> {
	<span style="color:#a0a1a7"><em>// 妻子向丈夫请示</em></span>
	<span style="color:#a626a4">public</span> <span style="color:#a626a4">void</span> <span style="color:#4078f2">HandleMessage</span>(IWomen women) {
		System.out.println(<span style="color:#50a14f">"妻子的请示是："</span> + women.getRequest());
		System.out.println(<span style="color:#50a14f">"丈夫的答复是：同意"</span>);
	}
}

<span style="color:#a626a4">public</span> <span style="color:#a626a4">class</span> <span style="color:#4078f2">Son</span> <span style="color:#a626a4">implements</span> <span style="color:#4078f2">IHandler</span> {
	<span style="color:#a0a1a7"><em>// 母亲向儿子请示</em></span>
	<span style="color:#a626a4">public</span> <span style="color:#a626a4">void</span> <span style="color:#4078f2">HandleMessage</span>(IWomen women) {
		System.out.println(<span style="color:#50a14f">"母亲的请示是："</span> + women.getRequest());
		System.out.println(<span style="color:#50a14f">"儿子的答复是：同意"</span>);
	}
}
</code></span></span>
  • 场景类：
复制代码 
<span style="color:#141418"><span style="background-color:#ffffff"><code class="language-java"><span style="color:#a626a4">public</span> <span style="color:#a626a4">class</span> <span style="color:#4078f2">Client</span> {

	<span style="color:#a626a4">public</span> <span style="color:#a626a4">static</span> <span style="color:#a626a4">void</span> <span style="color:#4078f2">main</span>(String[] args) {
		<span style="color:#a0a1a7"><em>// 随机挑选几个女性</em></span>
		<span style="color:#986801">Random</span> <span style="color:#986801">rand</span> <span style="color:#ab5656">=</span> <span style="color:#a626a4">new</span> <span style="color:#4078f2">Random</span>();
		ArrayList<IWomen> arrayList = <span style="color:#a626a4">new</span> <span style="color:#4078f2">ArrayList</span>();
		<span style="color:#a626a4">for</span> (<span style="color:#986801">int</span> <span style="color:#986801">i</span> <span style="color:#ab5656">=</span> <span style="color:#986801">0</span>; i < <span style="color:#986801">5</span>; i++) {
			arrayList.add(<span style="color:#a626a4">new</span> <span style="color:#4078f2">Women</span>(rand.nextInt(<span style="color:#986801">4</span>), <span style="color:#50a14f">"看戏"</span>));
		}
		<span style="color:#a0a1a7"><em>// 定义三个请示对象</em></span>
		<span style="color:#986801">IHandler</span> <span style="color:#986801">father</span> <span style="color:#ab5656">=</span> <span style="color:#a626a4">new</span> <span style="color:#4078f2">Father</span>();
		<span style="color:#986801">IHandler</span> <span style="color:#986801">husband</span> <span style="color:#ab5656">=</span> <span style="color:#a626a4">new</span> <span style="color:#4078f2">Husband</span>();
		<span style="color:#986801">IHandler</span> <span style="color:#986801">son</span> <span style="color:#ab5656">=</span> <span style="color:#a626a4">new</span> <span style="color:#4078f2">Son</span>();
		<span style="color:#a626a4">for</span> (IWomen women : arrayList) {
			<span style="color:#a626a4">if</span> (women.getType() == <span style="color:#986801">1</span>) {
				<span style="color:#a0a1a7"><em>// 未结婚少女，请示父亲</em></span>
				System.out.println(<span style="color:#50a14f">"\n--------女儿向父亲请示-------"</span>);
				father.HandleMessage(women);
			} <span style="color:#a626a4">else</span> <span style="color:#a626a4">if</span> (women.getType() == <span style="color:#986801">2</span>) {
				<span style="color:#a0a1a7"><em>// 已婚少妇，请示丈夫</em></span>
				System.out.println(<span style="color:#50a14f">"\n--------妻子向丈夫请示-------"</span>);
				husband.HandleMessage(women);
			} <span style="color:#a626a4">else</span> <span style="color:#a626a4">if</span> (women.getType() == <span style="color:#986801">3</span>) {
				<span style="color:#a0a1a7"><em>// 母亲请示儿子</em></span>
				System.out.println(<span style="color:#50a14f">"\n--------母亲向儿子请示-------"</span>);
				son.HandleMessage(women);
			} <span style="color:#a626a4">else</span> {
				<span style="color:#a0a1a7"><em>// 暂时什么也不做</em></span>
			}
		}
	}

}
</code></span></span>

首先是通过随机方法产生了5个古代妇女的对象，然后看她们是如何就看戏这件事去请示的，运行结果如下：

在这里插入图片描述

OK，业务已经实现了，但是明显这个业务实现是存在问题的。

● 职责界定不清晰
对女儿提出的请示，应该在父亲类中做出决定，父亲有责任、有义务处理女儿的请示， 因此Father类应该是知道女儿的请求自己处理，而不是在Client类中进行组装出来，也就是说原本应该是父亲这个类做的事情抛给了其他类进行处理。

● 代码臃肿
我们在Client类中写了if...else的判断条件，而且能随着能处理该类型的请示人员越多，if...else的判断就越多。

● 耦合过重
这是什么意思呢，我们要根据Women的type来决定使用IHandler的那个实现类来处理请 求。有一个问题是：如果IHandler的实现类继续扩展怎么办？如果修改Client类，那就违背了开闭原则。

● 异常情况欠考虑
妻子只能向丈夫请示吗？如果妻子（比如一个现代女性穿越到古代了，不懂什么“三从四德”）向自己的父亲请示了，父亲应该做何处理？我们的程序上可没有体现出来，逻辑失败了！

引入责任链模式

针对上面的问题，这时候就该考虑引入责任链模式了。

可以抽象成这样一个结构，女性的请求先发送到父亲类，父亲类一看是自己要处理的，就 作出回应处理，如果女儿已经出嫁了，那就要把这个请求转发到女婿来处理，那女婿一旦去天国报道了，那就由儿子来处理这个请求，类似于如图16-3所示的顺序处理图：

图16-3:女性请示的顺序处理图

在这里插入图片描述

父亲、丈夫、儿子每个节点有两个选择：要么承担责任，做出回应；要么把请求转发到后序环节。

根据责任链模式，修改后的类图如下：

图16-4:使用责任链模式后的女子“三从”类图

在这里插入图片描述

实现如下：

  • 改造后的Handler类：
复制代码 
<span style="color:#141418"><span style="background-color:#ffffff"><code class="language-java"><span style="color:#a626a4">public</span> <span style="color:#a626a4">abstract</span> <span style="color:#a626a4">class</span> <span style="color:#4078f2">Handler</span> {
	<span style="color:#a626a4">public</span> <span style="color:#a626a4">final</span> <span style="color:#a626a4">static</span> <span style="color:#986801">int</span> <span style="color:#986801">FATHER_LEVEL_REQUEST</span> <span style="color:#ab5656">=</span> <span style="color:#986801">1</span>;
	<span style="color:#a626a4">public</span> <span style="color:#a626a4">final</span> <span style="color:#a626a4">static</span> <span style="color:#986801">int</span> <span style="color:#986801">HUSBAND_LEVEL_REQUEST</span> <span style="color:#ab5656">=</span> <span style="color:#986801">2</span>;
	<span style="color:#a626a4">public</span> <span style="color:#a626a4">final</span> <span style="color:#a626a4">static</span> <span style="color:#986801">int</span> <span style="color:#986801">SON_LEVEL_REQUEST</span> <span style="color:#ab5656">=</span> <span style="color:#986801">3</span>;
	<span style="color:#a0a1a7"><em>// 能处理的级别</em></span>
	<span style="color:#a626a4">private</span> <span style="color:#986801">int</span> <span style="color:#986801">level</span> <span style="color:#ab5656">=</span> <span style="color:#986801">0</span>;
	<span style="color:#a0a1a7"><em>// 责任传递，下一个人责任人是谁</em></span>
	<span style="color:#a626a4">private</span> Handler nextHandler;

	<span style="color:#a0a1a7"><em>// 每个类都要说明一下自己能处理哪些请求</em></span>
	<span style="color:#a626a4">public</span> <span style="color:#4078f2">Handler</span>(<span style="color:#986801">int</span> _level) {
		<span style="color:#c18401">this</span>.level = _level;
	}

	<span style="color:#a0a1a7"><em>// 一个女性（女儿、妻子或者是母亲）要求逛街，你要处理这个请求</em></span>
	<span style="color:#a626a4">public</span> <span style="color:#a626a4">final</span> <span style="color:#a626a4">void</span> <span style="color:#4078f2">HandleMessage</span>(IWomen women) {
		<span style="color:#a626a4">if</span> (women.getType() == <span style="color:#c18401">this</span>.level) {
			<span style="color:#c18401">this</span>.response(women);
		} <span style="color:#a626a4">else</span> <span style="color:#a626a4">if</span> (<span style="color:#c18401">this</span>.nextHandler != <span style="color:#0184bb">null</span>) {
			<span style="color:#a0a1a7"><em>// 有后续环节，才把请求往后递送</em></span>
			<span style="color:#c18401">this</span>.nextHandler.HandleMessage(women);
		} <span style="color:#a626a4">else</span> {
			<span style="color:#a0a1a7"><em>// 已经没有后续处理人了，不用处理了</em></span>
			System.out.println(<span style="color:#50a14f">"---没地方请示了，按不同意处理---\n"</span>);
		}
	}

	<span style="color:#a0a1a7"><em>/** 如果不属于你处理的请求，你应该让她找下一个环节的人，如女儿出嫁了， * 还向父亲请示是否可以逛街，那父亲就应该告诉女儿，应该找丈夫请示 */</em></span>
	<span style="color:#a626a4">public</span> <span style="color:#a626a4">void</span> <span style="color:#4078f2">setNext</span>(Handler _handler) {
		<span style="color:#c18401">this</span>.nextHandler = _handler;
	}

<span style="color:#a0a1a7"><em>//有请示那当然要回应</em></span>
	<span style="color:#a626a4">protected</span> <span style="color:#a626a4">abstract</span> <span style="color:#a626a4">void</span> <span style="color:#4078f2">response</span>(IWomen women);
}
</code></span></span>

在这里也用到模板方法模式，在模板方法中判断请求的级别和当前能够处理的级别，如果相同则调用基本方法，做出 反馈；如果不相等，则传递到下一个环节，由下一环节做出回应，如果已经达到环节结尾， 则直接做不同意处理。基本方法response需要各个实现类实现，每个实现类只要实现两个职 责：一是定义自己能够处理的等级级别；二是对请求做出回应。

三个实现类如下：三个实现类分别处理不同等级的请求

  • 父亲类：
复制代码 
<span style="color:#141418"><span style="background-color:#ffffff"><code class="language-java"><span style="color:#a626a4">public</span> <span style="color:#a626a4">class</span> <span style="color:#4078f2">Father</span> <span style="color:#a626a4">extends</span> <span style="color:#4078f2">Handler</span> {
	<span style="color:#a0a1a7"><em>// 父亲只处理女儿的请求</em></span>
	<span style="color:#a626a4">public</span> <span style="color:#4078f2">Father</span>() {
		<span style="color:#c18401">super</span>(Handler.FATHER_LEVEL_REQUEST);
	}

	<span style="color:#a0a1a7"><em>// 父亲的答复</em></span>
	<span style="color:#a626a4">protected</span> <span style="color:#a626a4">void</span> <span style="color:#4078f2">response</span>(IWomen women) {
		System.out.println(<span style="color:#50a14f">"--------女儿向父亲请示-------"</span>);
		System.out.println(women.getRequest());
		System.out.println(<span style="color:#50a14f">"父亲的答复是:同意\n"</span>);
	}
}
</code></span></span>
  • 丈夫类：
复制代码 
<span style="color:#141418"><span style="background-color:#ffffff"><code class="language-java"><span style="color:#a626a4">public</span> <span style="color:#a626a4">class</span> <span style="color:#4078f2">Husband</span> <span style="color:#a626a4">extends</span> <span style="color:#4078f2">Handler</span> {
	<span style="color:#a0a1a7"><em>// 丈夫只处理妻子的请求</em></span>
	<span style="color:#a626a4">public</span> <span style="color:#4078f2">Husband</span>() {
		<span style="color:#c18401">super</span>(Handler.HUSBAND_LEVEL_REQUEST);
	}

<span style="color:#a0a1a7"><em>//丈夫请示的答复 </em></span>
	<span style="color:#a626a4">protected</span> <span style="color:#a626a4">void</span> <span style="color:#4078f2">response</span>(IWomen women) {
		System.out.println(<span style="color:#50a14f">"--------妻子向丈夫请示-------"</span>);
		System.out.println(women.getRequest());
		System.out.println(<span style="color:#50a14f">"丈夫的答复是：同意\n"</span>);
	}
}
</code></span></span>
  • 儿子类：
复制代码 
<span style="color:#141418"><span style="background-color:#ffffff"><code class="language-java"><span style="color:#a626a4">public</span> <span style="color:#a626a4">class</span> <span style="color:#4078f2">Son</span> <span style="color:#a626a4">extends</span> <span style="color:#4078f2">Handler</span> {
	<span style="color:#a0a1a7"><em>// 儿子只处理母亲的请求</em></span>
	<span style="color:#a626a4">public</span> <span style="color:#4078f2">Son</span>() {
		<span style="color:#c18401">super</span>(Handler.SON_LEVEL_REQUEST);
	}

	<span style="color:#a0a1a7"><em>// 儿子的答复</em></span>
	<span style="color:#a626a4">protected</span> <span style="color:#a626a4">void</span> <span style="color:#4078f2">response</span>(IWomen women) {
		System.out.println(<span style="color:#50a14f">"--------母亲向儿子请示-------"</span>);
		System.out.println(women.getRequest());
		System.out.println(<span style="color:#50a14f">"儿子的答复是：同意\n"</span>);
	}
}
</code></span></span>

  • Women类的接口没有任何变化

  • 实现类稍微有些变化：为了展示结果清晰一点，输出请求的来源

复制代码 
<span style="color:#141418"><span style="background-color:#ffffff"><code class="language-java"><span style="color:#a626a4">public</span> <span style="color:#a626a4">class</span> <span style="color:#4078f2">Women</span> <span style="color:#a626a4">implements</span> <span style="color:#4078f2">IWomen</span> {
	<span style="color:#a0a1a7"><em>/**
	 * 通过一个int类型的参数来描述妇女的个人状况 1--未出嫁 * 2--出嫁 * 3--夫死
	 */</em></span>
	<span style="color:#a626a4">private</span> <span style="color:#986801">int</span> <span style="color:#986801">type</span> <span style="color:#ab5656">=</span> <span style="color:#986801">0</span>;
	<span style="color:#a0a1a7"><em>// 妇女的请示</em></span>
	<span style="color:#a626a4">private</span> <span style="color:#986801">String</span> <span style="color:#986801">request</span> <span style="color:#ab5656">=</span> <span style="color:#50a14f">""</span>;

	<span style="color:#a0a1a7"><em>// 构造函数传递过来请求</em></span>
	<span style="color:#a626a4">public</span> <span style="color:#4078f2">Women</span>(<span style="color:#986801">int</span> _type, String _request) {
		<span style="color:#c18401">this</span>.type = _type; <span style="color:#a0a1a7"><em>// 为了便于显示，在这里做了点处理</em></span>
		<span style="color:#a626a4">switch</span> (<span style="color:#c18401">this</span>.type) {
		<span style="color:#a626a4">case</span> <span style="color:#986801">1</span>:
			<span style="color:#c18401">this</span>.request = <span style="color:#50a14f">"女儿的请求是："</span> + _request;
			<span style="color:#a626a4">break</span>;
		<span style="color:#a626a4">case</span> <span style="color:#986801">2</span>:
			<span style="color:#c18401">this</span>.request = <span style="color:#50a14f">"妻子的请求是："</span> + _request;
			<span style="color:#a626a4">break</span>;
		<span style="color:#a626a4">case</span> <span style="color:#986801">3</span>:
			<span style="color:#c18401">this</span>.request = <span style="color:#50a14f">"母亲的请求是："</span> + _request;
		}
	}

	<span style="color:#a0a1a7"><em>// 获得自己的状况</em></span>
	<span style="color:#a626a4">public</span> <span style="color:#986801">int</span> <span style="color:#4078f2">getType</span>() {
		<span style="color:#a626a4">return</span> <span style="color:#c18401">this</span>.type;
	}

	<span style="color:#a0a1a7"><em>// 获得妇女的请求</em></span>
	<span style="color:#a626a4">public</span> String <span style="color:#4078f2">getRequest</span>() {
		<span style="color:#a626a4">return</span> <span style="color:#c18401">this</span>.request;
	}
}
</code></span></span>

  • 场景类：
复制代码 
<span style="color:#141418"><span style="background-color:#ffffff"><code class="language-java"><span style="color:#a626a4">public</span> <span style="color:#a626a4">class</span> <span style="color:#4078f2">Client</span> {
	<span style="color:#a626a4">public</span> <span style="color:#a626a4">static</span> <span style="color:#a626a4">void</span> <span style="color:#4078f2">main</span>(String[] args) {
		<span style="color:#a0a1a7"><em>// 随机挑选几个女性</em></span>
		<span style="color:#986801">Random</span> <span style="color:#986801">rand</span> <span style="color:#ab5656">=</span> <span style="color:#a626a4">new</span> <span style="color:#4078f2">Random</span>();
		ArrayList<IWomen> arrayList = <span style="color:#a626a4">new</span> <span style="color:#4078f2">ArrayList</span>();
		<span style="color:#a626a4">for</span> (<span style="color:#986801">int</span> <span style="color:#986801">i</span> <span style="color:#ab5656">=</span> <span style="color:#986801">0</span>; i < <span style="color:#986801">5</span>; i++) {
			arrayList.add(<span style="color:#a626a4">new</span> <span style="color:#4078f2">Women</span>(rand.nextInt(<span style="color:#986801">4</span>), <span style="color:#50a14f">"我要看戏"</span>));
		}
		<span style="color:#a0a1a7"><em>// 定义三个请示对象</em></span>
		<span style="color:#986801">Handler</span> <span style="color:#986801">father</span> <span style="color:#ab5656">=</span> <span style="color:#a626a4">new</span> <span style="color:#4078f2">Father</span>();
		<span style="color:#986801">Handler</span> <span style="color:#986801">husband</span> <span style="color:#ab5656">=</span> <span style="color:#a626a4">new</span> <span style="color:#4078f2">Husband</span>();
		<span style="color:#986801">Handler</span> <span style="color:#986801">son</span> <span style="color:#ab5656">=</span> <span style="color:#a626a4">new</span> <span style="color:#4078f2">Son</span>();
		<span style="color:#a0a1a7"><em>// 设置请示顺序</em></span>
		father.setNext(husband);
		husband.setNext(son);
		<span style="color:#a626a4">for</span> (IWomen women : arrayList) {
			father.HandleMessage(women);
		}
	}
}
</code></span></span>

在Client中设置请求的传递顺序，先向父亲请示，不是父亲应该解决的问题，则由父亲 传递到丈夫类解决，若不是丈夫类解决的问题则传递到儿子类解决，最终的结果必然有一个 返回，其运行结果如下所示：

在这里插入图片描述

业务调用类Client不用再去做判断到底是需要谁去处理，而且Handler抽象类的子类可以继续增加下去，只需要扩展传递链而已，调用类可以不用了解变化过程，甚至是谁在处理这个请求都不用知道。

责任链模式优缺点

责任链模式优点

  • 责任链模式使得一个对象无须知道是其他哪一个对象处理其请求，对象仅需知道该请求会 被处理即可，接收者和发送者都没有对方的明确信息，且链中的对象不需要知道链的结构， 由客户端负责链的创建，降低了系统的耦合度。
  • 请求处理对象仅需维持一个指向其后继者的引用，而不需要维持它对所有的候选处理者的 引用，可简化对象的相互连接。
  • 在给对象分派职责时，职责链可以给我们更多的灵活性，可以通过在运行时对该链进行动 态的增加或修改来增加或改变处理一个请求的职责。
  • 在系统中增加一个新的具体请求处理者时无须修改原有系统的代码，只需要在客户端重新 建链即可，从这一点来看是符合“开闭原则”的。

责任链模式缺点

  • 由于一个请求没有明确的接收者，那么就不能保证它一定会被处理，该请求可能一直到链 的末端都得不到处理；一个请求也可能因职责链没有被正确配置而得不到处理。
  • 对于比较长的职责链，请求的处理可能涉及到多个处理对象，系统性能将受到一定影响， 而且在进行代码调试时不太方便。
  • 如果建链不当，可能会造成循环调用，将导致系统陷入死循环。

责任链模式应用场景

在以下情况下可以考虑使用职责链模式：

  • 有多个对象可以处理同一个请求，具体哪个对象处理该请求待运行时刻再确定，客户端只 需将请求提交到链上，而无须关心请求的处理对象是谁以及它是如何处理的。
  • 在不明确指定接收者的情况下，向多个对象中的一个提交一个请求。
  • 可动态指定一组对象处理请求，客户端可以动态创建职责链来处理请求，还可以改变链中 处理者之间的先后次序。

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