设计模式之职责链模式

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受者对象的链。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另一个接收者的引用。如果一个对象不能处理该请求，那么他会把相同的请求传给下一个接收者，依次类推

3）这种类型的设计模式属于行为型模式

说白了，就是流水线，不是自己整的活就由流下去直到有人做完为止

例子：采购审批流程

金额 小于等于5000 由主任批

金额 小于等于10000由院长批

金额 小于等于30000由副校长批

金额 超过30000 由校长批

public abstract class Approver {Approver approver;//下一个处理者String name;public Approver(String name) {this.name = name;}public void setApprover(Approver approver) {this.approver = approver;}//处理审批请求方法public abstract void processRequest(PurchaseRequest purchaseRequest);
}

public class DepartmentApprover extends Approver{public DepartmentApprover(String name) {super(name);}@Overridepublic 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);}}
}

public class CollegeApprover extends Approver{public CollegeApprover(String name) {super(name);}@Overridepublic 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);}}
}

public class ViceSchoolMasterApprover extends Approver{public ViceSchoolMasterApprover(String name) {super(name);}@Overridepublic 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);}}
}

public class SchoolMasterApprover extends Approver{public SchoolMasterApprover(String name) {super(name);}@Overridepublic 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);}}
}

public class PurchaseRequest {private int type;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;}
}

public class Client {public static void main(String[] args) {//创建一个请求PurchaseRequest purchaseRequest = new PurchaseRequest(1, 31000, 1);DepartmentApprover departmentApprover = new DepartmentApprover("张主任");CollegeApprover collegeApprover = new CollegeApprover("李院长");ViceSchoolMasterApprover viceSchoolMasterApprover = new ViceSchoolMasterApprover("韩副校长");SchoolMasterApprover schoolMasterApprover = new SchoolMasterApprover("周校长");//将各个级别的下一个处理者设置好departmentApprover.setApprover(collegeApprover);collegeApprover.setApprover(viceSchoolMasterApprover);viceSchoolMasterApprover.setApprover(schoolMasterApprover);schoolMasterApprover.setApprover(departmentApprover);//形成环形departmentApprover.processRequest(purchaseRequest);}
}
/**
请求编号id =1被周校长处理
**/

SpringMVC-HandlerExecutionChain类就使用到职责链模式

总结
1）将请求和处理分开，实现解耦，提高灵活性
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，因此需要控制链中最大节点数量，一般通过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，避免出现超长链无意识的破坏系统性能
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