行为型——责任链模式

news2025/3/31 22:49:58

责任链模式

责任链模式是一种行为型设计模式，它允许请求沿着处理链传递，直到有一个处理者处理为止。其核心思想是解耦请求发送者与接收者。

特点

解耦处理者与接收者: 发送者无需知道哪一个接收者处理请求，接收者也无需知道请求的细节。
动态构建处理链: 灵活的调整处理者的顺序或增减处理者。
责任明确: 每个处理者只负责处理特定的请求。

模式结构

角色	描述
抽象处理者(Handler)	定义了处理请求的接口，并且可以访问它的后继者
具体处理者(ConcreteHandler)	实现了处理请求的接口，判断是否可以处理该请求，否则将请求传递给它的后继者
客户端(Client)	创建处理链，并向链的头部发起请求

简单示例

from abc import ABC, abstractmethod
from typing import Optional


# 处理者抽象类
class Approver(ABC):

    def __init__(self):
        self._successor: Optional[Approver] = None

    def set_successor(self, successor: 'Approver') -> 'Approver':
        self._successor = successor
        return successor

    @abstractmethod
    def handle_request(self, amount: float) -> str:
        pass


# 具体处理者类
class Supervisor(Approver):
    def handle_request(self, amount: str) -> str:
        if amount <= 500:
            return f'Supervisor approved ${amount} Reimbursement.'
        elif self._successor:
            return self._successor.handle_request(amount)
        else:
            return f'${amount} Reimbursement denied.'

class DepartmentManager(Approver):
    def handle_request(self, amount: str) -> str:
        if amount <= 1000:
            return f'Department Manager approved ${amount} Reimbursement.'
        elif self._successor:
            return self._successor.handle_request(amount)
        else:
            return f'${amount} Reimbursement denied.'

class CEO(Approver):
    def handle_request(self, amount: str) -> str:
        if amount <= 10000:
            return f'CEO approved ${amount} Reimbursement.'
        elif self._successor:
            return self._successor.handle_request(amount)
        else:
            return f'${amount} Reimbursement denied.'

# 客户端代码
if __name__ == '__main__':
    supervisor = Supervisor()
    department_manager = DepartmentManager()
    ceo = CEO()
    supervisor.set_successor(department_manager).set_successor(ceo)

    requests = [250, 600, 1250, 10000]
    for amount in requests:
        print(supervisor.handle_request(amount))

    # 结果输出
    # Supervisor approved $250.0 Reimbursement.
    # Department Manager approved $600.0 Reimbursement.
    # CEO approved $1250.0 Reimbursement.
    # 10000 Reimbursement denied.