c++11工厂子类实现自注册的两种方法

文章目录

一、产品类构建
- 1. 猫基类与各品种猫子类
- 2.狗基类与各品种狗子类
二、工厂类构建
三、客户端使用switch-case实现调用不同工厂子类
四、自注册方法一：公开注册函数显式注册
五、自注册方法二：构造函数隐形注册
总结

一、产品类构建

1. 猫基类与各品种猫子类

class Cat {public:virtual void Printer() = 0;
};class Persian : public Cat {public:virtual void Printer() {std::cout<<"I am a cat, persian."<<std::endl;}
};class Birman : public Cat {public:virtual void Printer() {std::cout<<"I am a cat, Birman."<<std::endl;}
};class NorwegianForestCat : public Cat {public:virtual void Printer() {std::cout<<"I am a Norwegian Forest Cat."<<std::endl;}
};class Ragdoll : public Cat {public:virtual void Printer() {std::cout<<"I am a Cat, Ragdoll."<<std::endl;}
};class Himalayan : public Cat {public:virtual void Printer() {std::cout<<"I am a Cat, Himalayan."<<std::endl;}
};

2.狗基类与各品种狗子类

class Dog {public:virtual void Printer() = 0;
};class Affenpinscher : public Dog {public:virtual void Printer() {std::cout<<"I am a Dog, Affenpinscher"<<std::endl;;}
};class AfghanHound  : public Dog {public:virtual void Printer() {std::cout<<"I am a Dog, Afghan Hound "<<std::endl;;}
};class AiredaleTerrier  : public Dog {public:virtual void Printer() {std::cout<<"I am a Dog, Airedale Terrier "<<std::endl;;}
};class Akita  : public Dog {public:virtual void Printer() {std::cout<<"I am a Dog, Akita "<<std::endl;;}
};class AlaskanMalamute  : public Dog {public:virtual void Printer() {std::cout<<"I am a Dog, Alaskan Malamute "<<std::endl;;}
};

二、工厂类构建

现在假设有五家动物繁育工厂，Animal1Factory，Animal2Factory，Animal3Factory，Animal4Factory，Animal5Factory。

Animal1Factoryt负责繁育的品种猫与狗分别为：Persian与Affenpinscher；
Animal2Factory负责繁育的品种猫与狗分别为：Birman与AfghanHound；
Animal3Factory负责繁育的品种猫与狗分别为：NorwegianForestCat与AiredaleTerrier；
Animal4Factory负责繁育的品种猫与狗分别为：Ragdoll与Akita；
Animal5Factory负责繁育的品种猫与狗分别为：Himalayan与AlaskanMalamute。

可构建动物繁育工厂基类：

class AnimalFactory {public:virtual Cat *produceCat() = 0;virtual Dog *produceDog() = 0;
};

其他五个动物繁育工厂子类构建如下：

class Animal1Factory : public AnimalFactory{public:Cat *produceCat(){return new Persian();}Dog *produceDog(){return new Affenpinscher();}
}; class Animal2Factory : public AnimalFactory{public:Cat *produceCat(){return new Birman();}Dog *produceDog(){return new AfghanHound();}
};class Animal3Factory : public AnimalFactory{public:Cat *produceCat(){return new Ragdoll();}Dog *produceDog(){return new AiredaleTerrier();}
};class Animal4Factory : public AnimalFactory{public:Cat *produceCat(){return new NorwegianForestCat();}Dog *produceDog(){return new Akita();}
};
class Animal5Factory : public AnimalFactory{public:Cat *produceCat(){return new Himalayan();}Dog *produceDog(){return new AlaskanMalamute();}
};

三、客户端使用switch-case实现调用不同工厂子类

对以上构建的各产品类与工厂类，可在客户端使用switch-case根据不同的key去创建不同的派生工厂类对象，实现产生该工厂繁育的品种猫与狗。

int main(int argc, char **argv)
{for (size_t i = 0; i < 100; i++){AnimalFactory* factory = 0;int factory_name;std::cout<<"please input the factory index: ";std::cin>>factory_name;switch (factory_name) {case 1:factory = new Animal1Factory();break;case 2:factory = new Animal2Factory();break;case 3:factory = new Animal3Factory();break;case 4:factory = new Animal4Factory();break;case 5:factory = new Animal5Factory();break;default:break;}if (factory != 0){Cat* cat = factory->produceCat();Dog* dog = factory->produceDog();cat->Printer();dog->Printer();}        }return 0;
}

输出如下：

如果工厂子类个数已经确定，个数也不多的时候，用switch-case来调用工厂子类没啥问题。但是，随着工厂子类数越来越多，这个switch-case结构就显得有点傻了。例如，一个具有将近100多个工厂子类库，维护这样一个switch-case简直是肉疼。并且，switch-case调用工厂子类方式对于需要突然新增工厂子类的项目非常不友好。下面将要介绍的工厂子类自注册方法，便是解决该问题的一个很好的途径。

四、自注册方法一：公开注册函数显式注册

这是介绍的两种自注册方法之一，利用类内的公开注册函数显示注册工厂子类。另一种是在构造函数中隐式注册自己。我个人更加偏爱于后者。

自注册的方法，将各子类共用一个注册表，在构造完后与实例化前，将子类注册进全局的注册表。

对工厂基类新增一些功能函数，用来注册新的工厂子类，并从注册表中获取某一子类：

class AnimalFactory {public:virtual Cat *produceCat() = 0;virtual Dog *produceDog() = 0;static AnimalFactory* GetInstance(std::string name){_instance = LookUp(name);return _instance;}static void Register(const std::string name, AnimalFactory* func){AnimalFactory* regist = LookUp(name); // 防止重复注册，保证各子类的唯一性if (regist != NULL){return;}else{registry_.insert(std::make_pair(name, func));}}
protected: static AnimalFactory* LookUp(std::string name){std::map<std::string, AnimalFactory*>::iterator iter = registry_.find(name);if (iter != registry_.end())return iter->second;elsereturn NULL;        }
private:static std::map<std::string, AnimalFactory*> registry_; static AnimalFactory* _instance;
}; AnimalFactory* AnimalFactory::_instance = NULL;
std::map<std::string, AnimalFactory*> AnimalFactory::registry_;

各工厂子类增加静态函数static void Regist() ，具体代码如下所示：

class Animal1Factory : public AnimalFactory{public:Cat *produceCat(){return new Persian();}Dog *produceDog(){return new Affenpinscher();}static void Regist(){AnimalFactory::Register("Animal1Factory", new Animal1Factory());}
}; class Animal2Factory : public AnimalFactory{public:Cat *produceCat(){return new Birman();}Dog *produceDog(){return new AfghanHound();}static void Regist(){AnimalFactory::Register("Animal2Factory", new Animal2Factory());}
};class Animal3Factory : public AnimalFactory{public:Cat *produceCat(){return new Ragdoll();}Dog *produceDog(){return new AiredaleTerrier();}static void Regist(){AnimalFactory::Register("Animal3Factory", new Animal3Factory());}
};class Animal4Factory : public AnimalFactory{public:Cat *produceCat(){return new NorwegianForestCat();}Dog *produceDog(){return new Akita();}static void Regist(){AnimalFactory::Register("Animal4Factory", new Animal4Factory());}
};class Animal5Factory : public AnimalFactory{public:Cat *produceCat(){return new Himalayan();}Dog *produceDog(){return new AlaskanMalamute();}static void Regist(){AnimalFactory::Register("Animal5Factory", new Animal5Factory());}
};

客户端调用工厂子类如下：

static void before_main()
{std::cout<<"regist sub factory..."<<std::endl;Animal1Factory::Regist();Animal2Factory::Regist();Animal3Factory::Regist();Animal4Factory::Regist();Animal5Factory::Regist();
}int main(int argc, char **argv)
{before_main();for (size_t i = 0; i < 100; i++){AnimalFactory* factory = 0;std::string factory_name;std::cout<<"please input the factory name: ";std::cin>>factory_name;factory = AnimalFactory::GetInstance(factory_name);if (factory != 0){Cat* cat = factory->produceCat();Dog* dog = factory->produceDog();cat->Printer();dog->Printer();}        }return 0;
}

输出如下：

五、自注册方法二：构造函数隐形注册

上面介绍的自注册方法，需要在使用工厂子类前，在客户端对各子类进行一个显式可见的注册。这样做对于使用它们的客户仍不是很友好。现在介绍一种在构造函数内隐形注册的方法，此方法不需要用户在客户端对各工厂子类进行注册。

工厂基类与第一种自注册方法一样
各子类工厂的构造函数中添加Animal1Factory(){AnimalFactory::Register("Animal1Factory", this);}，并在子类未尾添加该子类的一个静态实例，具体代码如下：

class Animal1Factory : public AnimalFactory{public:Cat *produceCat(){return new Persian();}Dog *produceDog(){return new Affenpinscher();}Animal1Factory(){AnimalFactory::Register("Animal1Factory", this);}
};
static Animal1Factory animal1factory;class Animal2Factory : public AnimalFactory{public:Cat *produceCat(){return new Birman();}Dog *produceDog(){return new AfghanHound();}Animal2Factory(){AnimalFactory::Register("Animal2Factory", this);}
};
static Animal2Factory animal2factory; // 添加一个静态实例，实现该子类的注册class Animal3Factory : public AnimalFactory{public:Cat *produceCat(){return new Ragdoll();}Dog *produceDog(){return new AiredaleTerrier();}Animal3Factory(){AnimalFactory::Register("Animal3Factory", this);}
};
static Animal3Factory animal3factory;class Animal4Factory : public AnimalFactory{public:Cat *produceCat(){return new NorwegianForestCat();}Dog *produceDog(){return new Akita();}Animal4Factory(){AnimalFactory::Register("Animal4Factory", this);}
};
static Animal4Factory animal4factory;class Animal5Factory : public AnimalFactory{public:Cat *produceCat(){return new Himalayan();}Dog *produceDog(){return new AlaskanMalamute();}Animal5Factory(){AnimalFactory::Register("Animal5Factory", this);}
};
static Animal5Factory animal5factory;

客户端调用工厂子类如下（注意，此时已经在客户端见不到注册的痕迹）：

int main(int argc, char **argv)
{for (size_t i = 0; i < 100; i++){AnimalFactory* factory = 0;std::string factory_name;std::cout<<"please input the factory name: ";std::cin>>factory_name;factory = AnimalFactory::GetInstance(factory_name);if (factory != 0){Cat* cat = factory->produceCat();Dog* dog = factory->produceDog();cat->Printer();dog->Printer();}        }return 0;
}

输出：

总结

利用C++工厂方法，可以灵活的实现丰富的功能。正如工厂方法里的名词：工厂-产品，工厂负责生产产品。不同的工厂会产生同样类型的产品，就像衣服有很多种品牌（工厂），然后，衣服也粗分为裤子、外套等（产品）。在工厂-产品模式下，自注册其实分为两层：1）新产品越来越多，需要对新产品进行注册；2）新增加的品牌也会越来越多，需要对新工厂进行注册。网上对前一种注册应用介绍较多，因此，本文在工厂子类自注册应用背景下对自注册方法进行介绍。自注册避免了客户端调用冗长的switch-case，其中利用公开注册函数仍需要在正式使用子类前，对各子类进行注册，构造函数注册法则将注册隐藏在类文件中，当新工厂出现时，客户代码具有最好的兼容性。