学校的采购审批项目

1. 如果金额小于等于5000，由教学主任审批
2. 如果金额小于等于10000，由院长审批
3. 如果金额小于等于30000，由副校长审批
4. 如果金额大于30000，由校长审批

传统方案解决

传统方案的问题

1. 传统方式解决问题是接收一个采购项目后，根据采购金额来调用对应的Approver完成审批
2. 客户端会使用到分支判断来处理不同的采购请求，这样的话如果相关审批员可审核价格改变客户端需要重写。另外客户端需要知道每个审批员的可审核金额，存在强耦合不利于扩展

职责链模式

基本介绍

1. 职责链模式又叫责任链模式，为请求创建一个接收者对象的链，这种模式对请求的发送者和接收者解耦
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，如果一个对像不能处理该请求，那么他会把相同的请求传递给下一个接收者
3. 职责链模式属于行为型模式

原理类图

1. Handler：抽象的处理者，定义了一个处理请求的接口，同时含有另外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，如果可以处理当前请求，则处理，否则就将该请求交给后继者处理，从而形成一个职责链
3. Request表示一个请求

职责链模式解决问题

代码实现
1.PurchaseRequest

//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;}
}

2.Approver

public abstract class Approver {Approver approver;  //下一个处理者String name; // 名字public Approver(String name) {// TODO Auto-generated constructor stubthis.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);}

DepartmentApprover

public class DepartmentApprover extends Approver {public DepartmentApprover(String name) {// TODO Auto-generated constructor stubsuper(name);}@Overridepublic void processRequest(PurchaseRequest purchaseRequest) {// TODO Auto-generated method stubif(purchaseRequest.getPrice() <= 5000) {System.out.println(" 请求编号 id= " + purchaseRequest.getId() + " 被 " + this.name + " 处理");}else {approver.processRequest(purchaseRequest);}}}

CollegeApprover

public class CollegeApprover extends Approver {public CollegeApprover(String name) {// TODO Auto-generated constructor stubsuper(name);}@Overridepublic void processRequest(PurchaseRequest purchaseRequest) {// TODO Auto-generated method stubif(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);}}
}

ViceSchoolMasterApprover

public class ViceSchoolMasterApprover extends Approver {public ViceSchoolMasterApprover(String name) {// TODO Auto-generated constructor stubsuper(name);}@Overridepublic void processRequest(PurchaseRequest purchaseRequest) {// TODO Auto-generated method stubif(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);}}
}

SchoolMasterApprover

public class SchoolMasterApprover extends Approver {public SchoolMasterApprover(String name) {// TODO Auto-generated constructor stubsuper(name);}@Overridepublic void processRequest(PurchaseRequest purchaseRequest) {// TODO Auto-generated method stubif(purchaseRequest.getPrice() > 30000) {System.out.println(" 请求编号 id= " + purchaseRequest.getId() + " 被 " + this.name + " 处理");}else {approver.processRequest(purchaseRequest);}}
}

3.Client

public class Client {public static void main(String[] args) {// TODO Auto-generated method stub//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);viceSchoolMasterApprover.processRequest(purchaseRequest);}}

职责链模式的应用

SpringMVC-HandlerExceptionChain类使用到了职责链模式，慢慢来。。

职责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，特别是链比较长的时候，因此需要控制链的最大节点数量，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阈值，超过则不允许该链建立避免出现超长链
• 适用于有多个对象可以处理同一请求时