什么是责任链设计模式? 责任链设计模式 —> 行为型模式
1、如果金额 0< X <=5000,由教学主任审批; 2、如果金额 5000< X <=10000,由院长审批; 3、如果金额 10000< X <=30000,由副校长审批; 4、如果金额 X >30000 以上,由校长审批。
创建请求 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 public class PurchaseRequest { private int type = 0 ; private float price = 0.0f ; private int id = 0 ; public PurchaseRequest (int type, float price, int id) { this .type = type; this .price = price; this .id = id; } public int getType () { return type; } public float getPrice () { return price; } public int getId () { return id; } }
处理者 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 public abstract class Approver { Approver approver; String name; public Approver (String name) { this .name = name; } public void setApprover (Approver approver) { this .approver = approver; } public abstract void processRequest (PurchaseRequest purchaseRequest) ; }
主任处理 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 public class DepartmentApprover extends Approver { public DepartmentApprover (String name) { super (name); } @Override public void processRequest (PurchaseRequest purchaseRequest) { if (purchaseRequest.getPrice() <= 5000 ) { System.out.println("请求编号 id= " + purchaseRequest.getId() + "被" + this .name + "处理!" ); } else { approver.processRequest(purchaseRequest); } } }
院长处理 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 public class CollegeApprover extends Approver { public CollegeApprover (String name) { super (name); } @Override public void processRequest (PurchaseRequest purchaseRequest) { if (purchaseRequest.getPrice() > 5000 && purchaseRequest.getPrice() <= 10000 ) { System.out.println("请求编号 id= " + purchaseRequest.getId() + "被" + this .name + "处理!" ); } else { approver.processRequest(purchaseRequest); } } }
副校长处理 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 public class ViceSchoolMasterApprover extends Approver { public ViceSchoolMasterApprover (String name) { super (name); } @Override public void processRequest (PurchaseRequest purchaseRequest) { if (purchaseRequest.getPrice() > 10000 && purchaseRequest.getPrice() <= 30000 ) { System.out.println("请求编号 id= " + purchaseRequest.getId() + "被" + this .name + "处理!" ); } else { approver.processRequest(purchaseRequest); } } }
校长处理 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 public class SchoolMasterApprover extends Approver { public SchoolMasterApprover (String name) { super (name); } @Override public void processRequest (PurchaseRequest purchaseRequest) { if (purchaseRequest.getPrice() > 30000 ) { System.out.println("请求编号 id= " + purchaseRequest.getId() + "被" + this .name + "处理!" ); } else { approver.processRequest(purchaseRequest); } } }
客户端 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 public class Client { public static void main (String[] args) { PurchaseRequest purchaseRequest = new PurchaseRequest(1 , 5100 , 1 ); DepartmentApprover departmentApprover = new DepartmentApprover("主任" ); CollegeApprover collegeApprover = new CollegeApprover("院长" ); ViceSchoolMasterApprover viceSchoolMasterApprover = new ViceSchoolMasterApprover("副校长" ); SchoolMasterApprover schoolMasterApprover = new SchoolMasterApprover("校长" ); departmentApprover.setApprover(collegeApprover); collegeApprover.setApprover(viceSchoolMasterApprover); viceSchoolMasterApprover.setApprover(schoolMasterApprover); schoolMasterApprover.setApprover(departmentApprover); departmentApprover.processRequest(purchaseRequest); viceSchoolMasterApprover.processRequest(purchaseRequest); } }
责任链模式的注意事项和细节
将请求和处理分开,实现解耦,提高系统的灵活性;
简化了对象,使对象不需要知道链的结构;
性能会受到影响,特别是在链比较长的时候,因此需控制链中最大节点数量,一般通过在 Handler 中设置一个最大节点数量,在 setNext() 方法中判断是否已经超过阀值,超过则不允许该链建立,避免出现超长链无意识地破坏系统性能;
调试不方便。采用了类似递归的方式,调试时逻辑可能比较复杂;
最佳应用场景:有多个对象可以处理同一个请求时,比如:多级请求、请假/加薪等审批流程、JavaWeb中Tomcat对Encoding的处理、拦截器。
职责链模式在 SpringMVC 应用场景 SpringMVC 中 HandlerExecutionChain 就使用到了职责链模式。
SpringMVC 请求的流程中,执行了拦截器相关方法 interceptor preHandler 等;
在处理 SpringMvc 请求时,使用到责任链模式还使用到适配器模式;
HandlerExecutionChain 主要负责的是请求拦截器的执行和请求处理,但是他本身不处理请求,只是将请求分配给链上注册处理器执行,这是职责链实现方式,减少职责链本身与处理逻辑之间的耦合,规范了处理流程;
HandlerExecutionChain 维护了 HandlerInterceptor 集合,可以向其中注册相应拦截器。
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