GOF 23 设计模式之 责任链模式（Chain Of Responsibility）

定义：

• 将能够处理同一类请求的对象连成一条链，所提交的请求验者链传递，链上的对象逐个判断是否有能力处理该请求，如果能则处理，如果不能则传递给链上的下一个对象。

场景

• 打牌时，轮流出牌
• 接力赛跑
• 大学中，奖学金审批
• 公司里，公文审批

实现方式

• 链表方式定义职责链
• 非链表方式定义职责链
  
  • 通过集合、数组生成职责链更加实用！实际上，很多项目中，每个具体的Handler并不是由开发团队定义的，而是项目上线后由外部单位追加的，所以使用链表方式定义COR链就很困难

开发中常见的场景

• Java中，异常机制就是一种责任链模式。一个try可以对应多个catch，当第一个catch不匹配类型，则自动跳到第二个catch
• Javascript语言中，事件的冒泡和捕获机制。Java语言中，事件的处理采用观察者模式
• Servlet开发中，过滤器的链式处理
• Struts2中，拦截器的调用也是经典的责任链模式

代码实现

• LeaveRequest

package com.coderbean.chainOfResp;/** * 请假的基本信息 * Created by Chang on 15/10/3. */public class LeaveRequest {    private String name;    private int leaveDays;    private String reason;    public LeaveRequest(String name, int leaveDays, String reason) {        this.name = name;        this.leaveDays = leaveDays;        this.reason = reason;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public int getLeaveDays() {        return leaveDays;    }    public void setLeaveDays(int leaveDays) {        this.leaveDays = leaveDays;    }    public String getReason() {        return reason;    }    public void setReason(String reason) {        this.reason = reason;    }}

• Leader

package com.coderbean.chainOfResp;/** * Created by Chang on 15/10/3. */public abstract class Leader {    protected String name;    protected Leader nextLeader;    //责任链伤的后继对象    public Leader(String name) {        this.name = name;    }    public void setNextLeader(Leader nextLeader) {        this.nextLeader = nextLeader;    }    public abstract void handleRequest(LeaveRequest request);}

• Director

package com.coderbean.chainOfResp;/** * Created by Chang on 15/10/3. */public class Director extends Leader {    public Director(String name) {        super(name);    }    @Override    public void handleRequest(LeaveRequest request) {        if(request.getLeaveDays()<3){            System.out.println("员工"+request.getName()+"请假"+request.getLeaveDays()+"天");            System.out.println("主任:审批通过");        }else{            if(this.nextLeader!=null){                this.nextLeader.handleRequest(request);            }        }    }}

• Manager

package com.coderbean.chainOfResp;/** * Created by Chang on 15/10/3. */public class Manager extends Leader {    public Manager(String name) {        super(name);    }    @Override    public void handleRequest(LeaveRequest request) {        if(request.getLeaveDays()<10){            System.out.println("员工"+request.getName()+"请假"+request.getLeaveDays()+"天");            System.out.println("经理:审批通过");        }else{            if(this.nextLeader!=null){                this.nextLeader.handleRequest(request);            }        }    }}

• GeneralManager

package com.coderbean.chainOfResp;/** * Created by Chang on 15/10/3. */public class GeneralManager extends Leader {    public GeneralManager(String name) {        super(name);    }    @Override    public void handleRequest(LeaveRequest request) {        if(request.getLeaveDays()<30){            System.out.println("员工"+request.getName()+"请假"+request.getLeaveDays()+"天");            System.out.println("总经理:审批通过");        }else{            System.out.println("莫非"+request.getName()+"想辞职,居然请假"+request.getLeaveDays()+"天");        }    }}

• Client

package com.coderbean.chainOfResp;/** * Created by Chang on 15/10/3. */public class Client {    public static void main(String[] args) {        Leader a = new Director("张三");        Leader b = new Manager("李四");        Leader c = new GeneralManager("王五");        a.setNextLeader(b);        b.setNextLeader(c);        LeaveRequest request = new LeaveRequest("TOM",100,"会英国老家探亲");        a.handleRequest(request);    }}