Python设计模式-中介者模式

Python设计模式-中介者模式

代码基于3.5.2，代码如下;

#coding:utf-8
#中介者模式

class colleague():
    mediator = None
    def __init__(self,mediator):
        self.mediator = mediator

class purchaseColleague(colleague):
    def buyStuff(self,num):
        print("PURCHASE:Bought {0}".format(num))
        self.mediator.execute("buy",num)
    def getNotice(self,content):
        print("PURCHASE:Get Notice -- {0}".format(content))

class warehoustColleague(colleague):
    total = 0
    threshold = 100
    def setThreshold(self,threshold):
        self.threshold = threshold
    def isEnough(self):
        if self.total < self.threshold:
            print("WARNING:Warning ... Stock is low ..")
            self.mediator.execute("warning",self.total)
            return False
        else:
            return True
    def inc(self,num):
        self.total += num
        print("WAREHOUSE:Increase {0}".format(num))
        self.mediator.execute("increase",num)
    def dec(self,num):
        if num > self.total:
            print("WAREHOUSE：Error ... Stock is not enough")
        else:
            self.total -= num
            print("WAREHOUSE:Decrease {0}".format(num))
            self.mediator.execute("decrease",num)
        self.isEnough()

class salesColleague(colleague):
    def sellStuff(self,num):
        print("SALES:Sell {0}".format(num))
        self.mediator.execute("sell",num)
    def getNotice(self,content):
        print("SALES:Get Notice -- {0}".format(content))

class abstractMediator():
    purchase = None
    sales = None
    warehouse = None
    def setPurchase(self,purchase):
        self.purchase = purchase
    def setWarehouse(self,warehouse):
        self.warehouse = warehouse
    def setSales(self,sales):
        self.sales = sales
    def execute(self,content,num):
        pass

class stockMediator(abstractMediator):
    def execute(self,content,num):
        print("MEDIATOR:Get Info -- {0}".format(content))
        if content == "buy":
            self.warehouse.inc(num)
            self.sales.getNotice("Bought {0}".format(num))
        elif content == "increase":
            self.sales.getNotice("Inc {0}".format(num))
            self.purchase.getNotice("Inc {0}".format(num))
        elif content == "decrease":
            self.sales.getNotice("Dec {0}".format(num))
            self.purchase.getNotice("Dec {0}".format(num))
        elif content == "warning":
            self.sales.getNotice("Stock is low {0} left".format(num))
            self.purchase.getNotice("Stock is low. Please Buy More {0}".format(num))
        elif content == "sell":
            self.warehouse.dec(num)
            self.purchase.getNotice("Sold {0}".format(num))
        else:
            pass

if __name__ == "__main__":
    mobile_mediator = stockMediator()
    mobile_purchase = purchaseColleague(mobile_mediator)
    moblie_warehouse = warehoustColleague(mobile_mediator)
    moblie_sales = salesColleague(mobile_mediator)
    mobile_mediator.setPurchase(mobile_purchase)
    mobile_mediator.setWarehouse(moblie_warehouse)
    mobile_mediator.setSales(moblie_sales)

    moblie_warehouse.setThreshold(200)
    mobile_purchase.buyStuff(300)
    moblie_sales.sellStuff(120)

中介者模式分析与解读

中介者模式

中介者模式，用一个中介对象来封装一系列的对象交互。中介者使各对象不需要显式地相互引用，从而使其耦合松散，而且可以独立地改变它们之间的交互。

代码解读

该例子基于的需求:销售一旦达成订单，销售人员会通过系统的销售子系统部分通知仓储子系统，仓储子系统会将可出仓手机数量减少，同时通知采购管理子系统当前销售订单；仓储子系统的库存到达阈值以下，会通知销售子系统和采购子系统，并督促采购子系统采购；采购完成后，采购人员会把采购信息填入采购子系统，采购子系统会通知销售子系统采购完成，并通知仓库子系统增加库存。
1、定义了colleague类，子系统都是通过继承该子类来实现，在该类初始化时，传入mediator者；
2、分别定义了purchaseColleague、warehoustColleague和salesColleague三个类，分别表示采购子系统，仓库子系统和销售子系统，在purchaseColleague中的buyStuff、salesColleague的sellStuff方法，都是在接收到请求处理时调用了mediator的方法处理；在warehoustColleague仓储子系统类中，每次调用inc，dec方法，都是先判断保存的total、threshold值是否在要求范围内，当total数量小于threshold时，会通过调用mediator来通知采购子系统，当total数量增加时，通知销售子系统仓储数量增加；
3、通过定义abstractMediator来保存三个子系统的实例，stockMediator通过继承abstractMediator类，实现execute方法，来实现三个子系统在调用过程中的逻辑处理，以此来完成通信。

代码运行结果如下:
PURCHASE:Bought 300
MEDIATOR:Get Info -- buy
WAREHOUSE:Increase 300
MEDIATOR:Get Info -- increase
SALES:Get Notice -- Inc 300
PURCHASE:Get Notice -- Inc 300
SALES:Get Notice -- Bought 300
SALES:Sell 120
MEDIATOR:Get Info -- sell
WAREHOUSE:Decrease 120
MEDIATOR:Get Info -- decrease
SALES:Get Notice -- Dec 120
PURCHASE:Get Notice -- Dec 120
WARNING:Warning ... Stock is low ..
MEDIATOR:Get Info -- warning
SALES:Get Notice -- Stock is low 180 left
PURCHASE:Get Notice -- Stock is low. Please Buy More 180
PURCHASE:Get Notice -- Sold 120

中介者模式应用场景:

1、设计类图时，出现了网状结构时，可以考虑将类图设计成星型结构，这样就可以实现中介模式；
2、适用于一组对象以定义良好但是复杂的方式进行通信的场合；
3、想定制一个分布在多个类中的行为，而又不想生成太多的子类的场合。

优缺点分析

优点

1、减少类与类的依赖，降低了类和类之间的耦合；
2、容易扩展规模。

缺点

1、当处理逻辑较多时，会造成中介者本身的复杂性较大。