责任链模式(Chain of Responsibility Pattern)

1 代码

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。



In [2]:

    
class manager():
    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：



In [3]:

    
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)









    



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

2 Discriptions

责任链模式的定义如下：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。

3 Advantages

将请求者与处理者分离，请求者并不知道请求是被哪个处理者所处理，易于扩展。

4 Usages

若一个请求可能由一个对请求有链式优先级的处理群所处理时，可以考虑责任链模式。

5 Disadvantages

如果责任链比较长，会有比较大的性能问题；
如果责任链比较长，若业务出现问题，比较难定位是哪个处理者的问题。