13-Python与设计模式--责任链模式

Posted 2021-02-01 漫天飞雪

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一、请假系统

假设有这么一个请假系统：员工若想要请3天以内（包括3天的假），只需要直属经理批准就可以了；如果想请3-7天，不仅需要直属经理批准，部门经理需要最终批准；如果请假大于7天，不光要前两个经理批准，也需要总经理最终批准。类似的系统相信大家都遇到过，那么该如何实现呢？首先想到的当然是if…else…，但一旦遇到需求变动，其臃肿的代码和复杂的耦合缺点都显现出来。简单分析下需求，“假条”在三个经理间是单向传递关系，像一条链条一样，因而，我们可以用一条“链”把他们进行有序连接。
构造抽象经理类和各个层级的经理类：

class manager():
    successor = None
    name = \'\'
    def __init__(self, name):
        self.name = name
    def setSuccessor(self, successor):
        self.successor = successor
    def handleRequest(self, request):
        pass
class lineManager(manager):
    def handleRequest(self, request):
        if request.requestType == \'DaysOff\' and request.number <= 3:
            print \'%s:%s Num:%d Accepted OVER\' % (self.name, request.requestContent, request.number)
        else:
            print \'%s:%s Num:%d Accepted CONTINUE\' % (self.name, request.requestContent, request.number)
            if self.successor != None:
                self.successor.handleRequest(request)
class departmentManager(manager):
    def handleRequest(self, request):
        if request.requestType == \'DaysOff\' and request.number <= 7:
            print \'%s:%s Num:%d Accepted OVER\' % (self.name, request.requestContent, request.number)
        else:
            print \'%s:%s Num:%d Accepted CONTINUE\' % (self.name, request.requestContent, request.number)
            if self.successor != None:
                self.successor.handleRequest(request)
class generalManager(manager):
    def handleRequest(self, request):
        if request.requestType == \'DaysOff\':
            print \'%s:%s Num:%d Accepted OVER\' % (self.name, request.requestContent, request.number)
class request():
    requestType = \'\'
    requestContent = \'\'
    number = 0

request类封装了假期请求。在具体的经理类中，可以通过setSuccessor接口来构建“责任链”，并在handleRequest接口中实现逻辑。场景类中实现如下：

if  __name__=="__main__":
    line_manager = lineManager(\'LINE MANAGER\')
    department_manager = departmentManager(\'DEPARTMENT MANAGER\')
    general_manager = generalManager(\'GENERAL MANAGER\')

    line_manager.setSuccessor(department_manager)
    department_manager.setSuccessor(general_manager)

    req = request()
    req.requestType = \'DaysOff\'
    req.requestContent = \'Ask 1 day off\'
    req.number = 1
    line_manager.handleRequest(req)

    req.requestType = \'DaysOff\'
    req.requestContent = \'Ask 5 days off\'
    req.number = 5
    line_manager.handleRequest(req)

    req.requestType = \'DaysOff\'
    req.requestContent = \'Ask 10 days off\'
    req.number = 10
    line_manager.handleRequest(req)

打印如下：

LINE MANAGER:Ask 1 day off Num:1 Accepted OVER
LINE MANAGER:Ask 5 days off Num:5 Accepted CONTINUE
DEPARTMENT MANAGER:Ask 5 days off Num:5 Accepted OVER
LINE MANAGER:Ask 10 days off Num:10 Accepted CONTINUE
DEPARTMENT MANAGER:Ask 10 days off Num:10 Accepted CONTINUE
GENERAL MANAGER:Ask 10 days off Num:10 Accepted OVER

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