设计模式之二十二之职责链模式
模式介绍
1) 职责链模式(Chain of Responsibility Pattern), 又叫 责任链模式,为请求创建了一个接收者 对象的链(简单示意图)。这种模式对请求的 发送者和接收者进行解耦。
2) 职责链模式通常每个接收者都包含对另一个接 收者的引用。如果一个对象不能处理该请求, 那么它会把相同的请求传给下一个接收者,依 此类推。
3) 这种类型的设计模式属于行为型模式
uml图
对原理类图的说明-即(职责链模式的角色及职责)
1) Handler : 抽象的处理者, 定义了一个处理请求的接口, 同时含义另外Handler
2) ConcreteHandlerA , B 是具体的处理者, 处理它自己负责的请求, 可以访问它的后继者(即下一个处 理者), 如果可以处理当前请求,则处理,否则就将该请求交个 后继者去处理,从而形成一个职责链
3) Request , 含义很多属性,表示一个请求
案列
uml图
代码实现
package com.hy.responsibilitychain; /** * @author hanyong * @date 2020/12/18 0:11 */ public abstract class Approver { Approver approver; //下一个处理者 String name; // 名字 public Approver(String name) { // TODO Auto-generated constructor stub this.name = name; } //下一个处理者 public void setApprover(Approver approver) { this.approver = approver; } //处理审批请求的方法,得到一个请求, 处理是子类完成,因此该方法做成抽象 public abstract void processRequest(PurchaseRequest purchaseRequest); } package com.hy.responsibilitychain; /** * @author hanyong * @date 2020/12/18 0:18 */ public class CollegeApprover extends Approver { public CollegeApprover(String name) { // TODO Auto-generated constructor stub super(name); } @Override public void processRequest(PurchaseRequest purchaseRequest) { // TODO Auto-generated method stub if(purchaseRequest.getPrice() < 5000 && purchaseRequest.getPrice() <= 10000) { System.out.println(" 请求 id= " + purchaseRequest.getId() + " 院主任 " + this.name + " 处理问题"); }else { approver.processRequest(purchaseRequest); } } } package com.hy.responsibilitychain; /** * @author hanyong * @date 2020/12/18 0:12 */ 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 id= " + purchaseRequest.getId() + " 系主任" + this.name + " 处理问题"); } else { approver.processRequest(purchaseRequest); } } } package com.hy.responsibilitychain; /** * @author hanyong * @date 2020/12/18 0:20 */ public class SchoolMasterApprover extends Approver { public SchoolMasterApprover(String name) { // TODO Auto-generated constructor stub super(name); } @Override public void processRequest(PurchaseRequest purchaseRequest) { // TODO Auto-generated method stub if (purchaseRequest.getPrice() > 30000) { System.out.println(" 请求 id= " + purchaseRequest.getId() + " 校长 " + this.name + "处理问题"); } else { approver.processRequest(purchaseRequest); } } } package com.hy.responsibilitychain; /** * @author hanyong * @date 2020/12/18 0:19 */ public class ViceSchoolMasterApprover extends Approver { public ViceSchoolMasterApprover(String name) { // TODO Auto-generated constructor stub super(name); } @Override public void processRequest(PurchaseRequest purchaseRequest) { // TODO Auto-generated method stub if (purchaseRequest.getPrice() < 10000 && purchaseRequest.getPrice() <= 30000) { System.out.println(" 请求 id= " + purchaseRequest.getId() + " 副校长 " + this.name + " 处理问题"); } else { approver.processRequest(purchaseRequest); } } } package com.hy.responsibilitychain; /** * @author hanyong * @date 2020/12/18 0:11 */ //请求类 public class PurchaseRequest { private int type = 0; //请求类型 private float price = 0.0f; //请求金额 private int id = 0; //构造器 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; } } package com.hy.responsibilitychain; /** * @author hanyong * @date 2020/12/18 0:21 */ public class Client { public static void main(String[] args) { //创建一个请求 PurchaseRequest purchaseRequest = new PurchaseRequest(1, 31000, 1); //创建相关的审批人 DepartmentApprover departmentApprover = new DepartmentApprover("张主任"); CollegeApprover collegeApprover = new CollegeApprover("李院长"); ViceSchoolMasterApprover viceSchoolMasterApprover = new ViceSchoolMasterApprover("王副校"); SchoolMasterApprover schoolMasterApprover = new SchoolMasterApprover("佟校长"); //需要将各个审批级别的下一个设置好 (处理人构成环形: ) departmentApprover.setApprover(collegeApprover); collegeApprover.setApprover(viceSchoolMasterApprover); viceSchoolMasterApprover.setApprover(schoolMasterApprover); schoolMasterApprover.setApprover(departmentApprover); departmentApprover.processRequest(purchaseRequest); } }
执行结果
职责链模式的注意事项和细节
1) 将请求和处理分开,实现解耦,提高系统的灵活性
2) 简化了对象,使对象不需要知道链的结构
3) 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
4) 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
5) 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、Java Web中Tomcat对Encoding的处理、拦截器