设计模式之责任链模式讲解

概念：使多个对象都有机会处理请求，从而避免了请求的发送者和接收者之间的耦合关系。将这些对象连成一条链，并沿着这条链传递该请求，直到有对象处理它为止。最匹配的场景应该就是逐层审批的模式。

责任链模式只有两个角色，一个抽象处理类，一个具体处理类。这个模式的关键在于多个处理类层层持有，形成一个链条，并各自处理职责内的请求。

下面以一个请假审批的例子，帮助大家理解该模式。

public abstract class Approver {
    protected Approver nextApprover;
    public void setNextApprover(Approver nextApprover) {
        this.nextApprover = nextApprover;
    }
    public abstract void processRequest(LeaveRequest request);
}

public class TeamLead extends Approver {
    @Override
    public void processRequest(LeaveRequest request) {
        if (request.getDays() <= 2) {
            System.out.println("团队领导审批 " + request.getDays() + " 天假.");
        } else if (nextApprover != null) {
            System.out.println("发送上级经理审批。");
            nextApprover.processRequest(request);
        } else {
            System.out.println("超出团队领导审批权限。");
        }
    }
}

public class Manager extends Approver {
    @Override
    public void processRequest(LeaveRequest request) {
        if (request.getDays() <= 5) {
            System.out.println("经理审批 " + request.getDays() + " 天假.");
        } else if (nextApprover != null) {
            System.out.println("发送总监审批");
            nextApprover.processRequest(request);
        } else {
            System.out.println("超出经理审批范围");
        }
    }
}

public class Director extends Approver {
    @Override
    public void processRequest(LeaveRequest request) {
        if (request.getDays() <= 10) {
            System.out.println("总监审批 " + request.getDays() + " 天假.");
        } else {
            System.out.println("超出总监审批范围。");
        }
    }
}

public class LeaveRequest {
    private String employeeName;
    private int days;
    public LeaveRequest(String employeeName, int days) {
        this.employeeName = employeeName;
        this.days = days;
    }
    public String getEmployeeName() {
        return employeeName;
    }
    public int getDays() {
        return days;
    }
}

public class Demo {
    public static void main(String[] args) {
        TeamLead teamLead = new TeamLead();
        Manager manager = new Manager();
        Director director = new Director();
        teamLead.setNextApprover(manager);
        manager.setNextApprover(director);
        LeaveRequest request1 = new LeaveRequest("天哥", 2);
        LeaveRequest request2 = new LeaveRequest("天哥", 5);
        LeaveRequest request3 = new LeaveRequest("天哥", 10);
        LeaveRequest request4 = new LeaveRequest("天哥", 15);
        teamLead.processRequest(request1);
        System.out.println("**************************分割线*************************************");
        teamLead.processRequest(request2);
        System.out.println("**************************分割线*************************************");
        teamLead.processRequest(request3);
        System.out.println("**************************分割线*************************************");
        teamLead.processRequest(request4);
    }
}

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