Chain 责任链模式
目录
[TOC]
1. 概述
1.1. 设计模式定义
职责链模式（Chain of Responsibility）：使多个对象都有机会处理同一个请求，从而避免请求的发送者和接收者之间的耦合关系。将这些对象连成一条链，并沿着这条链传递该请求，直到有一个对象处理它为止。
1.2. 自我理解
责任链又叫做功能链，个人觉得有两种场景非常适合用：
1、流水线：层层配合，达到最后效果；每个人都要完成自己的工作，最后才能生产出产品；
链中的每个对象都要按照顺序处理，直到最后一个对象处理完毕。
2、责任划分：请假事宜，2天以内找组长，2~5天找经理，5~10天找总监，10~20天找副总….
链中的每个对象扮演处理器，并且有一个后继对象。如果它可以处理请求，就进行处理；否则把请求转发给后继者。
1.3. 责任链模式的组成
抽象链 (AbstractChain)：抽象类，抽象链路的下级引用，抽象执行方法。
具体链 (ConcreteChain)：抽项链的子类，具体链路的下级引用，具体执行方法，执行下个方法。
2. UML
3. Example
3.1. 场景
用户检验，一个用户登录需要通过层层检查，用户名、密码、权限等。该例子属于流水线式的责任链，所有具体链路全部执行完毕才能返回一个校验完成的用户。
这只是责任链中很简单的一个应用，有些银行的校验链路可以达到100多层。这么多层的校验，如果全部用 if else 去实现，后面的维护人员简直崩溃了。
3.2. 代码实现
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/** * Created * Date: 2021/07/27 00:34 <br/> * Description: 责任链模式 * * @author jomin@loserzhao.com * @see */ public class ChainPatternDemo { public static void main(String[] args) { // 初始化责任链 UserNameCheckChain -> PasswordCheckChain -> PermissionCheckChain PermissionCheckChain permissionCheckChain = new PermissionCheckChain(null); PasswordCheckChain passwordCheckChain = new PasswordCheckChain(permissionCheckChain); UserNameCheckChain userCheckChain = new UserNameCheckChain(passwordCheckChain); User userA = new User(null, null, null); User userB = new User("123", null, null); User userC = new User("123", "123", null); User userD = new User("123", "123", "123"); ResponseEnum responseAEnum = userCheckChain.check(userA); System.out.println("user A, status => [" + responseAEnum.getStatus() + "], message => [" + responseAEnum.getMessage() + "]"); ResponseEnum responseBEnum = userCheckChain.check(userB); System.out.println("user B, status => [" + responseBEnum.getStatus() + "], message => [" + responseBEnum.getMessage() + "]"); ResponseEnum responseCEnum = userCheckChain.check(userC); System.out.println("user C, status => [" + responseCEnum.getStatus() + "], message => [" + responseCEnum.getMessage() + "]"); ResponseEnum responseDEnum = userCheckChain.check(userD); System.out.println("user D, status => [" + responseDEnum.getStatus() + "], message => [" + responseDEnum.getMessage() + "]"); } public static abstract class UserCheckChain { protected UserCheckChain successor; protected UserCheckChain(UserCheckChain successor) { this.successor = successor; } protected abstract ResponseEnum check(User user, ResponseEnum responseEnum); protected ResponseEnum execute(User user, ResponseEnum responseEnum) { ResponseEnum response; // 如果正常，执行下一个规则 if (responseEnum.getStatus().equals(ResponseEnum.NORMAL.getStatus()) && null != successor) { response = successor.check(user, responseEnum); }else { response = responseEnum; } return response; } public ResponseEnum check(User user){ return check(user, ResponseEnum.NORMAL); } } public static class UserNameCheckChain extends UserCheckChain { public UserNameCheckChain(UserCheckChain userCheckChain){ super(userCheckChain); } @Override protected ResponseEnum check(User user, ResponseEnum responseEnum) { if (null == user || StringUtils.isEmpty(user.getUserName())) { responseEnum = ResponseEnum.USERNAME_NULL; } return execute(user, responseEnum); } } public static class PasswordCheckChain extends UserCheckChain { public PasswordCheckChain(UserCheckChain userCheckChain){ super(userCheckChain); } @Override protected ResponseEnum check(User user, ResponseEnum responseEnum) { if (null == user || StringUtils.isEmpty(user.getPassword())) { responseEnum = ResponseEnum.PASSWORD_NULL; } return execute(user, responseEnum); } } public static class PermissionCheckChain extends UserCheckChain { public PermissionCheckChain(UserCheckChain userCheckChain){ super(userCheckChain); } @Override protected ResponseEnum check(User user, ResponseEnum responseEnum) { if (null == user || StringUtils.isEmpty(user.getPermission())) { responseEnum = ResponseEnum.NO_PERMISSION; } return execute(user, responseEnum); } } public static enum ResponseEnum { NORMAL(0, "正常"), USERNAME_NULL(1, "用户名不能为空"), PASSWORD_NULL(2, "密码不能为空"), NO_PERMISSION(3, "权限不足"); private Integer status; private String message; ResponseEnum(Integer status, String message) { this.status = status; this.message = message; } public Integer getStatus() { return status; } public String getMessage() { return message; } } public static class User { private String userName; private String password; private String permission; public User() { } public User(String userName, String password, String permission) { this.userName = userName; this.password = password; this.permission = permission; } public String getUserName() { return userName; } public void setUserName(String userName) { this.userName = userName; } public String getPassword() { return password; } public void setPassword(String password) { this.password = password; } public String getPermission() { return permission; } public void setPermission(String permission) { this.permission = permission; } } } |
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