设计模式之责任链模式

1、核心

将能够处理同一类请求的对象连成一条链，所提交的请求沿着链传递，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。

2、应用场景

-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，拦截器的调用也是典型的责任链模式

3、代码示例

问题场景：
公司里面，请假条的审批过程：

如果请假天数小于3天，主任审批；
如果请假天数大于等于3天，小于10天，经理审批；
如果大于等于10天，小于30天，总经理审批；
如果大于等于30天，提示拒绝。

/** * 请假条类：封装请假信息 * @author ly1 * */public class LeaveRequest {    /**     * 请假者姓名     */    private String name;    /**     * 请假天数     */    private int leaveOfDays;    /**     * 请假原因     */    private String reason;    public LeaveRequest(String name, int leaveOfDays, String reason) {        super();        this.name = name;        this.leaveOfDays = leaveOfDays;        this.reason = reason;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public int getLeaveOfDays() {        return leaveOfDays;    }    public void setLeaveOfDays(int leaveOfDays) {        this.leaveOfDays = leaveOfDays;    }    public String getReason() {        return reason;    }    public void setReason(String reason) {        this.reason = reason;    }}

/** * 领导抽象类 * @author ly1 * */public abstract class Leader {    protected String name;    protected Leader nextLeader;    public Leader(String name) {        super();        this.name = name;    }    public void setNextLeader(Leader nextLeader) {        this.nextLeader = nextLeader;    }    public abstract void handleRequest(LeaveRequest request);}

/** * 主任类 * @author ly1 * */public class Director extends Leader{    public Director(String name) {        super(name);    }    @Override    public void handleRequest(LeaveRequest request) {        if(request.getLeaveOfDays() < 3){            System.out.println("员工：" + request.getName() + "请假，天数：" + request.getLeaveOfDays() + "，理由" + request.getReason());            System.out.println("主任：" + this.name + ",审批通过！");        }else{            this.nextLeader.handleRequest(request);        }    }}

/** * 经理类 * @author ly1 * */public class Manager extends Leader{    public Manager(String name) {        super(name);    }    @Override    public void handleRequest(LeaveRequest request) {        if(request.getLeaveOfDays() < 10){            System.out.println("员工：" + request.getName() + "请假，天数：" + request.getLeaveOfDays() + "，理由" + request.getReason());            System.out.println("经理：" + this.name + ",审批通过！");        }else{            this.nextLeader.handleRequest(request);        }    }}

/** * 总经理类 * @author ly1 * */public class GeneralManager extends Leader{    public GeneralManager(String name) {        super(name);    }    @Override    public void handleRequest(LeaveRequest request) {        if(request.getLeaveOfDays() < 30){            System.out.println("员工：" + request.getName() + "请假，天数：" + request.getLeaveOfDays() + "，理由" + request.getReason());            System.out.println("总经理：" + this.name + ",审批通过！");        }else{            System.out.println(request.getName()+",你是不想干了吧！");        }    }}

/** * 客户端调用 * @author ly1 * */public class Client {    public static void main(String[] args) {        Leader director = new Director("李主任");        Leader manager = new Manager("王经理");        Leader gManager = new GeneralManager("刘总经理");        director.setNextLeader(manager);        manager.setNextLeader(gManager);        LeaveRequest request1 = new LeaveRequest("Bob", 1, "休息");        director.handleRequest(request1);        LeaveRequest request2 = new LeaveRequest("Alice", 6, "十一黄金周");        director.handleRequest(request2);        LeaveRequest request3 = new LeaveRequest("Tom", 17, "出国旅游");        director.handleRequest(request3);    }}结果：员工：Bob请假，天数：1，理由休息主任：李主任,审批通过！员工：Alice请假，天数：6，理由十一黄金周经理：王经理,审批通过！员工：Tom请假，天数：17，理由出国旅游总经理：刘总经理,审批通过！