职责链模式

什么是职责链模式

职责链模式(Chain of Responsibility):使多个对象都有机会处理请求，从而避免请求的发送者和接收者之间的耦合关系。将这个对象连成一条链，并沿着这条链传递该请求，直到有一个对象处理它为止

通过示例了解职责链模式

职责链模式（Chain of Responsibility Pattern）是一种行为设计模式，它允许将请求沿着处理者对象的链式结构传递，直到某个对象处理它。下面是一个简单的Java职责链模式示例，用于处理不同级别的员工请假申请：

抽象处理者：员工接口

public interface Employee {void setNext(Employee employee);void processLeaveRequest(Integer leaveDays);
}

具体处理者：普通员工

public class RegularEmployee implements Employee {private Employee next;@Overridepublic void setNext(Employee employee) {this.next = employee;}@Overridepublic void processLeaveRequest(Integer leaveDays) {if (leaveDays <= 3) {System.out.println("Regular employee approved 3 days or less leave.");} else if (next != null) {System.out.println("Regular employee forwarded the request to higher authority.");next.processLeaveRequest(leaveDays);} else {System.out.println("Leave request exceeds regular employee's limit.");}}
}

具体处理者：主管

public class Manager implements Employee {private Employee next;@Overridepublic void setNext(Employee employee) {this.next = employee;}@Overridepublic void processLeaveRequest(Integer leaveDays) {if (leaveDays <= 7) {System.out.println("Manager approved 7 days or less leave.");} else if (next != null) {System.out.println("Manager forwarded the request to higher authority.");next.processLeaveRequest(leaveDays);} else {System.out.println("Leave request exceeds manager's limit.");}}
}

具体处理者：部门经理

public class DepartmentHead implements Employee {@Overridepublic void setNext(Employee employee) {// 不需要设置下一个处理者，因为部门经理是最高级别的审批人}@Overridepublic void processLeaveRequest(Integer leaveDays) {if (leaveDays <= 14) {System.out.println("Department head approved 14 days or less leave.");} else {System.out.println("Leave request exceeds department head's limit.");}}
}

主程序

public class ChainOfResponsibilityDemo {public static void main(String[] args) {Employee regular = new RegularEmployee();Employee manager = new Manager();Employee departmentHead = new DepartmentHead();regular.setNext(manager);manager.setNext(departmentHead);regular.processLeaveRequest(5); // 输出：Regular employee approved 3 days or less leave.regular.processLeaveRequest(8); // 输出：Regular employee forwarded the request to higher authority. Manager approved 7 days or less leave.regular.processLeaveRequest(16); // 输出：Regular employee forwarded the request to higher authority. Manager forwarded the request to higher authority. Leave request exceeds department head's limit.}
}

1. Employee接口是抽象处理者，定义了设置下一个处理者和处理请假申请的方法。
2. RegularEmployee, Manager, 和 DepartmentHead是具体处理者，实现了Employee接口，并根据各自的权限范围处理请假申请。
3. 职责链的建立是通过setNext方法将处理者对象链接在一起。
4. main方法展示了如何创建职责链，并通过processLeaveRequest方法处理不同数量的请假天数请求。

职责链模式允许在不增加额外的复杂性的情况下添加新的处理者，同时保持了请求的发送者和接收者的解耦。