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 {@Overridepublic 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 {@Overridepublic 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 {@Overridepublic 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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