一个个顺序挨着来 - 责任链模式（Chain of Responsibility Pattern）

责任链模式（Chain of Responsibility Pattern）

责任链模式（Chain of Responsibility Pattern）
- 责任链模式（Chain of Responsibility Pattern）概述
- - 责任链结构图
  - 责任链模式概述
  - 责任链模式涉及的角色
- talk is cheap， show you my code
- 总结

责任链模式（Chain of Responsibility Pattern）

责任链模式（Chain of Responsibility Pattern）是一种行为型设计模式，它允许你将请求沿着处理者链条传递，直到有一个处理者能够处理它为止。这种模式避免了请求发送者和接收者之间的耦合，并且可以动态地指定一组处理者来处理请求。每个处理者都包含对下一个处理者的引用，如果当前处理者不能处理请求，它会将请求转发给下一个处理者。

太抽象了，举个现实生活中的例子
生活中，我们可能会遇到需要报销的生活场景。但是报销的时候，每个人的报销权限不一样。比如金额比较小的时候，你的领导就可以帮你审批；但是如果金额超过了你领导的审核范围，你的领导可能就把报销的交给他的上一层领导处理；他的上一层领导如果能处理就处理，处理不了，就沿着审批链条再往上进行审批。

责任链模式（Chain of Responsibility Pattern）概述

责任链结构图

在这里插入图片描述

责任链模式概述

定义：使多个对象都有机会处理请求，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，并沿着这条链传递请求，直到有一个对象处理它为止。
目的：解耦请求的发送者与接收者，提供一个灵活的方式来处理请求，支持动态添加或移除处理逻辑。

责任链模式涉及的角色

抽象处理者（Handler）：声明了所有具体处理者必须实现的方法，通常是handle()方法。此外，它还可能包含一个指向下一个处理者的引用。

public abstract class Handler {protected Handler successor;public void setSuccessor(Handler successor) {this.successor = successor;}public abstract void handleRequest(String request);
}

具体处理者（ConcreteHandler）：实现了Handler接口的具体类。

public class ConcreteHandlerA extends Handler {@Overridepublic void handleRequest(String request) {if ("A".equals(request)) {System.out.println("Handled by ConcreteHandlerA");} else {if (successor != null) {successor.handleRequest(request);}}}
}public class ConcreteHandlerB extends Handler {@Overridepublic void handleRequest(String request) {if ("B".equals(request)) {System.out.println("Handled by ConcreteHandlerB");} else {if (successor != null) {successor.handleRequest(request);}}}
}

客户端（Client）：客户端创建具体的处理者对象，并根据需要将它们链接起来形成一条责任链。然后，客户端将请求传递给链中的第一个处理者。

public class Client {public static void main(String[] args) {Handler handlerA = new ConcreteHandlerA();Handler handlerB = new ConcreteHandlerB();// 构建责任链handlerA.setSuccessor(handlerB);// 发送请求handlerA.handleRequest("A"); // Handled by ConcreteHandlerAhandlerA.handleRequest("B"); // Handled by ConcreteHandlerBhandlerA.handleRequest("C"); // Not handled, no output or error}
}

talk is cheap， show you my code

我们还是利用本次要介绍的设计模式来实现我们给出的例子。

首先，我们定义一个ApprovalRequest类来表示审批请求：

public class ApprovalRequest {private double amount;private String description;private boolean isApproved = false;public ApprovalRequest(double amount, String description) {this.amount = amount;this.description = description;}public double getAmount() {return amount;}public String getDescription() {return description;}public boolean isApproved() {return isApproved;}public void setApproved(boolean approved) {isApproved = approved;}
}

接下来，我们定义一个Approver接口，所有审批者都将实现这个接口：

public interface Approver {void processRequest(ApprovalRequest request);Approver getNextApprover();void setNextApprover(Approver nextApprover);
}

我们为不同的审批级别创建具体的审批者类。例如，部门经理（DepartmentManager）、总监（Director）和CEO（ChiefExecutiveOfficer）

public class DepartmentManager implements Approver {private Approver nextApprover;private static final double LIMIT = 5000.0;public DepartmentManager() {}@Overridepublic void processRequest(ApprovalRequest request) {if (request.getAmount() <= LIMIT) {System.out.println(request.getDescription() + " is approved by Department Manager.");request.setApproved(true);} else {if (nextApprover != null) {nextApprover.processRequest(request);} else {System.out.println(request.getDescription() + " was rejected.");request.setApproved(false);}}}@Overridepublic Approver getNextApprover() {return nextApprover;}@Overridepublic void setNextApprover(Approver nextApprover) {this.nextApprover = nextApprover;}
}public class Director implements Approver {private Approver nextApprover;private static final double LIMIT = 20000.0;// Similar methods as in DepartmentManager// ...
}public class ChiefExecutiveOfficer implements Approver {private Approver nextApprover;// No limit for CEO, all requests will be approved or rejected here// Similar methods as in DepartmentManager and Director// ...
}

最后，我们可以编写一个客户端类来测试这个责任链：

public class Client {public static void main(String[] args) {ApprovalRequest request1 = new ApprovalRequest(4500, "Office supplies");ApprovalRequest request2 = new ApprovalRequest(12000, "New computer");ApprovalRequest request3 = new ApprovalRequest(25000, "Conference room renovation");Approver departmentManager = new DepartmentManager();Approver director = new Director();Approver ceo = new ChiefExecutiveOfficer();departmentManager.setNextApprover(director);director.setNextApprover(ceo);departmentManager.processRequest(request1);System.out.println("Request1 approved? " + request1.isApproved());departmentManager.processRequest(request2);System.out.println("Request2 approved? " + request2.isApproved());departmentManager.processRequest(request3);System.out.println("Request3 approved? " + request3.isApproved());}
}