23种设计模式中的责任链模式

允许多个对象都有机会处理请求，从而避免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，并沿着这条链传递请求，直到有一个处理器处理该请求为止。

责任链模式是一种处理请求的模式。它让多个处理器都有机会处理请求，直到其中某个处理成功为止。责任链模式把多个请求连成一条链，让请求在这条链上传递。

在实际场景中，财务审批就是一个责任链模式。

我们来看看如何实现责任链模式。

我们创建抽象类Approver ，然后创建4种不同级别的审核者，都扩展了Approver 。每个审核者都会比较自己的审核额度，如果有权限审核就直接审核通过，否则，将不审核，直接把请求传递给下一个审核者。

创建抽象审批者。

java">// 抽象审批者
public abstract class Approver {protected Approver nextApprover;protected String name;public Approver(String name) {this.name = name;}public void setNextApprover(Approver nextApprover) {this.nextApprover = nextApprover;}public abstract void processRequest(PurchaseRequest request);
}

创建扩展了该抽象审批者的具体类。

java">// 部门经理 - 可以审批不超过5000元的采购
public class DepartmentManager extends Approver {public DepartmentManager(String name) {super(name);}@Overridepublic void processRequest(PurchaseRequest request) {if (request.getAmount() <= 5000) {System.out.printf("部门经理 %s 审批了采购单: %s, 金额: %.2f元\n", name, request.getPurpose(), request.getAmount());} else if (nextApprover != null) {nextApprover.processRequest(request);}}
}

java">// 总监 - 可以审批不超过20000元的采购
public class Director extends Approver {public Director(String name) {super(name);}@Overridepublic void processRequest(PurchaseRequest request) {if (request.getAmount() <= 20000) {System.out.printf("总监 %s 审批了采购单: %s, 金额: %.2f元\n", name, request.getPurpose(), request.getAmount());} else if (nextApprover != null) {nextApprover.processRequest(request);}}
}

java">// 副总裁 - 可以审批不超过100000元的采购
public class VicePresident extends Approver {public VicePresident(String name) {super(name);}@Overridepublic void processRequest(PurchaseRequest request) {if (request.getAmount() <= 100000) {System.out.printf("副总裁 %s 审批了采购单: %s, 金额: %.2f元\n", name, request.getPurpose(), request.getAmount());} else if (nextApprover != null) {nextApprover.processRequest(request);}}
}

java">// 总裁 - 可以审批任何金额的采购
public class President extends Approver {public President(String name) {super(name);}@Overridepublic void processRequest(PurchaseRequest request) {System.out.printf("总裁 %s 审批了采购单: %s, 金额: %.2f元\n", name, request.getPurpose(), request.getAmount());}
}

采购请求类。

java">// 采购请求
public class PurchaseRequest {private double amount;  // 采购金额private String purpose; // 采购目的public PurchaseRequest(double amount, String purpose) {this.amount = amount;this.purpose = purpose;}public double getAmount() {return amount;}public String getPurpose() {return purpose;}
}

测试示例。

java">public class PurchaseApprovalDemo {public static void main(String[] args) {// 创建审批人Approver manager = new DepartmentManager("张经理");Approver director = new Director("李总监");Approver vp = new VicePresident("王副总裁");Approver president = new President("赵总裁");// 设置责任链manager.setNextApprover(director);director.setNextApprover(vp);vp.setNextApprover(president);// 创建采购请求PurchaseRequest request1 = new PurchaseRequest(4500, "购买办公用品");PurchaseRequest request2 = new PurchaseRequest(12000, "团队建设活动");PurchaseRequest request3 = new PurchaseRequest(50000, "服务器设备升级");PurchaseRequest request4 = new PurchaseRequest(150000, "新办公室装修");// 处理采购请求System.out.println("===== 采购审批流程开始 =====");manager.processRequest(request1);manager.processRequest(request2);manager.processRequest(request3);manager.processRequest(request4);System.out.println("===== 采购审批流程结束 =====");}
}