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1 | | -# **死磕设计模式之抽象责任链模式** |
| 1 | +# 死磕设计模式之抽象责任链模式 |
| 2 | + |
| 3 | +## 1 导读 |
| 4 | + |
| 5 | +### 1.1 定义 |
| 6 | + |
| 7 | +包含了一些命令对象和一系列处理对象。每个处理对象决定它能处理哪些命令对象,它也知道如何将它不能处理的命令对象传递给该链中的下一个处理对象。 |
| 8 | + |
| 9 | +该模式还描述了往该处理链的末尾添加新的处理对象的方法。 |
| 10 | + |
| 11 | +精简定义:为请求创建一个接收此次请求对象的链。 |
| 12 | + |
| 13 | +### 1.2 类型 |
| 14 | + |
| 15 | +行为型。 |
| 16 | + |
| 17 | +## 2 适用场景 |
| 18 | + |
| 19 | +一个请求的处理需要多个对象当中的一或几个协作处理。 |
| 20 | + |
| 21 | +## 3 优点 |
| 22 | + |
| 23 | +请求的发送者和接收者(请求的处理)解耦,责任链可动态组合。 |
| 24 | + |
| 25 | +## 4 缺点 |
| 26 | + |
| 27 | +- 责任链太长或者处理时间过长,影响性能 |
| 28 | +- 责任链有可能过多 |
| 29 | + |
| 30 | +## 5 设计模式对比 |
| 31 | + |
| 32 | +### 5.1 V.S 状态模式 |
| 33 | + |
| 34 | +- 各对象并不指定下一个所要处理的对象者,只有在客户端类设置链顺序及元素,直到被某个责任链处理或整条链结束 |
| 35 | +- 每个状态知道自己下一个所要处理的对象者是谁,即编译时确定 |
| 36 | + |
| 37 | +## 6 实战 |
| 38 | + |
| 39 | +```java |
| 40 | +package com.javaedge.design.pattern.behavioral.chainofresponsibility; |
| 41 | + |
| 42 | +import lombok.Getter; |
| 43 | +import lombok.Setter; |
| 44 | + |
| 45 | +/** |
| 46 | + * @author JavaEdge |
| 47 | + * @date 2019/1/19 |
| 48 | + */ |
| 49 | +@Getter |
| 50 | +@Setter |
| 51 | +public class Course { |
| 52 | + |
| 53 | + /** |
| 54 | + * 课程名 |
| 55 | + */ |
| 56 | + private String name; |
| 57 | + |
| 58 | + /** |
| 59 | + * 博客 |
| 60 | + */ |
| 61 | + private String article; |
| 62 | + |
| 63 | + /** |
| 64 | + * 视频 |
| 65 | + */ |
| 66 | + private String video; |
| 67 | +} |
| 68 | +``` |
| 69 | + |
| 70 | +```java |
| 71 | +package com.javaedge.design.pattern.behavioral.chainofresponsibility; |
| 72 | + |
| 73 | +import org.apache.commons.lang3.StringUtils; |
| 74 | + |
| 75 | +/** |
| 76 | + * 【具体实现类】审批人 |
| 77 | + * |
| 78 | + * @author JavaEdge |
| 79 | + */ |
| 80 | +public class ArticleApprover extends BaseApprover { |
| 81 | + |
| 82 | + @Override |
| 83 | + public void deploy(Course course) { |
| 84 | + if (StringUtils.isNoneBlank(course.getArticle())) { |
| 85 | + System.out.println(course.getName() + "含博客,批准!"); |
| 86 | + if (nextApprover != null) { |
| 87 | + nextApprover.deploy(course); |
| 88 | + } |
| 89 | + } else { |
| 90 | + System.out.println(course.getName() + "不含博客,拒绝!"); |
| 91 | + } |
| 92 | + } |
| 93 | +} |
| 94 | +``` |
| 95 | + |
| 96 | +```java |
| 97 | +package com.javaedge.design.pattern.behavioral.chainofresponsibility; |
| 98 | + |
| 99 | +/** |
| 100 | + * 审批人 |
| 101 | + * |
| 102 | + * @author JavaEdge |
| 103 | + */ |
| 104 | +public abstract class BaseApprover { |
| 105 | + |
| 106 | + protected BaseApprover nextApprover; |
| 107 | + |
| 108 | + public void setNextApprover(BaseApprover baseApprover) { |
| 109 | + this.nextApprover = baseApprover; |
| 110 | + } |
| 111 | + |
| 112 | + /** |
| 113 | + * 发布 |
| 114 | + * |
| 115 | + * @param course 课程 |
| 116 | + */ |
| 117 | + public abstract void deploy(Course course) ; |
| 118 | +} |
| 119 | +``` |
| 120 | + |
| 121 | +```java |
| 122 | +package com.javaedge.design.pattern.behavioral.chainofresponsibility; |
| 123 | + |
| 124 | +import org.apache.commons.lang3.StringUtils; |
| 125 | + |
| 126 | +import java.util.Objects; |
| 127 | + |
| 128 | +/** |
| 129 | + * 【具体实现类】审批人 |
| 130 | + * |
| 131 | + * @author JavaEdge |
| 132 | + */ |
| 133 | +public class VideoApprover extends BaseApprover { |
| 134 | + |
| 135 | + @Override |
| 136 | + public void deploy(Course course) { |
| 137 | + if (StringUtils.isNoneEmpty(course.getVideo())) { |
| 138 | + System.out.println(course.getName() + "含视频,批准!"); |
| 139 | + if (Objects.nonNull(nextApprover)) { |
| 140 | + nextApprover.deploy(course); |
| 141 | + } |
| 142 | + } else { |
| 143 | + System.out.println(course.getName() + "不含视频,拒绝!"); |
| 144 | + } |
| 145 | + } |
| 146 | +} |
| 147 | +``` |
| 148 | + |
| 149 | +UML: |
| 150 | + |
| 151 | + |
| 152 | + |
| 153 | +测试类: |
| 154 | + |
| 155 | +```java |
| 156 | +package com.javaedge.design.pattern.behavioral.chainofresponsibility; |
| 157 | + |
| 158 | +/** |
| 159 | + * @author JavaEdge |
| 160 | + */ |
| 161 | +public class Test { |
| 162 | + |
| 163 | + public static void main(String[] args) { |
| 164 | + BaseApprover articleApprover = new ArticleApprover(); |
| 165 | + BaseApprover videoApprover = new VideoApprover(); |
| 166 | + |
| 167 | + Course course = new Course(); |
| 168 | + course.setName("公众号-Learner"); |
| 169 | + course.setArticle("JavaEdge的博客"); |
| 170 | + course.setVideo("JavaEdge的小视频"); |
| 171 | + |
| 172 | + articleApprover.setNextApprover(videoApprover); |
| 173 | + articleApprover.deploy(course); |
| 174 | + } |
| 175 | +} |
| 176 | + |
| 177 | +output: |
| 178 | +公众号-Learner含博客,批准! |
| 179 | +公众号-Learner含视频,批准! |
| 180 | +``` |
| 181 | + |
| 182 | +将博客注释掉: |
| 183 | + |
| 184 | +```java |
| 185 | +public static void main(String[] args) { |
| 186 | + BaseApprover articleApprover = new ArticleApprover(); |
| 187 | + BaseApprover videoApprover = new VideoApprover(); |
| 188 | + |
| 189 | + Course course = new Course(); |
| 190 | + course.setName("公众号-Learner"); |
| 191 | +// course.setArticle("JavaEdge的博客"); |
| 192 | + course.setVideo("JavaEdge的小视频"); |
| 193 | + |
| 194 | + articleApprover.setNextApprover(videoApprover); |
| 195 | + articleApprover.deploy(course); |
| 196 | +} |
| 197 | + |
| 198 | +output: |
| 199 | +公众号-Learner不含博客,拒绝! |
| 200 | +``` |
| 201 | + |
| 202 | +## 7 框架应用 |
| 203 | + |
| 204 | +### 7.1 Tomcat#FilterChain |
| 205 | + |
| 206 | +FilterChain 是一个由 Servlet 容器提供给开发人员的对象,提供一个对资源的过滤请求的调用链的视图。 过滤器使用 FilterChain 调用链中的下一个过滤器,或如果调用过滤器是链中的最后一个过滤器,则调用链末尾的资源 |
| 207 | + |
| 208 | +```java |
| 209 | +public interface FilterChain { |
| 210 | + |
| 211 | + // 导致调用链中的下一个筛选器,或者如果调用筛选器是链中的最后一个筛选器, |
| 212 | + // 则会导致调用链末尾的资源 |
| 213 | + public void doFilter(ServletRequest request, ServletResponse response) |
| 214 | + throws IOException, ServletException; |
| 215 | +} |
| 216 | +``` |
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