设计模式之二十一:中介者模式(Mediator)

中介者模式：定义了一个对象，用来封装一系列对象的交互。中介者模式通过使对象之间不必显式引用降低了对象之间的耦合，并且允许你独立改变它们之间的交互。

中介者模式就是将对象之间的交互封装在了一个独立的对象中，这个独立的对象用来控制对象之间的交互行为，所以这个对象还是蛮复杂的。

UML类图：

主要包括：

1. Mediator：定义了一个Colleague对象之间交互的接口。
2. ConcreteMediator：实现了Colleague对象之间的交互行为，并了解和能操作Colleague对象。
3. Colleague classes：每一个Colleague都认识Mediator对象，并且通过Mediator来实现彼此之间的通讯。

基础C++代码如下：

#include <iostream>#include <string>using namespace std;class Colleague;class Mediator{    public:    virtual void send(string message,Colleague * c)=0;};class Colleague{        public:        Colleague(Mediator *m)        {            mediator=m;        }        void send(string message)        {            mediator->send(message,this);        }        virtual void notify(string message)=0;        protected:        Mediator * mediator;};class ConcreteColleague1:public Colleague{        public:        ConcreteColleague1(Mediator * c):Colleague(c)        {        }        void notify(string message)        {            cout<<"concreteColleague1 receive message:"<<message<<endl;        }};class ConcreteColleague2:public Colleague{        public:        ConcreteColleague2(Mediator *m):Colleague(m)        {        }        void notify(string message)        {            cout<<"concreteColleague2 receive message:"<<message<<endl;        }};class ConcreteMediator:public Mediator{    public:    void send(string message,Colleague * c)    {        ConcreteColleague1* c1=dynamic_cast<ConcreteColleague1 *>(c);        ConcreteColleague2* c2=dynamic_cast<ConcreteColleague2 *>(c);        if(c1!=NULL)        {            cc2->notify(message);        }        if(c2!=NULL)        {            cc1->notify(message);        }    }    void setCC1(ConcreteColleague1 * c)    {        cc1=c;    }       void setCC2(ConcreteColleague2 * c)    {        cc2=c;    }    private:    ConcreteColleague1 * cc1;    ConcreteColleague2 * cc2;};int main(){    ConcreteMediator *m=new ConcreteMediator();    ConcreteColleague1 * cc1=new ConcreteColleague1(m);    ConcreteColleague2 * cc2=new ConcreteColleague2(m);    m->setCC1(cc1);    m->setCC2(cc2);    cc1->send("how are you !");    cc2->send("fine ,thank you");    return 0;}

执行输出：

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一个使用中介者模式的聊天室的例子。这里实现了Mediator和Colleague的一对多的聚合关系，这样的中介者模式才是有意义的使用方式。
UML类图：

C++代码如下：

#include <iostream>#include <map>#include <string>using namespace std;class Participant;class AbstractChatRoom{        public:                virtual void registe(Participant * p)=0;                virtual void send(string from,string to ,string message)=0;};class ChatRoom:public AbstractChatRoom{        public:                void registe(Participant * p);                void send(string from,string to ,string message);        private:                map<Participant *,string> participants;};class Participant{        public:                Participant(string n=""):name(n)                {                }                string getName()                {                    return name;                }                void setChatRoom(ChatRoom *c)                {                    chatRoom=c;                }                void send(string to,string message)                {                    chatRoom->send(name,to,message);                }                virtual void receive(string from,string message)                {                    cout<<from<<" to "<<name<<" : "<<message<<endl;                }        private:                string name;                ChatRoom * chatRoom;};void ChatRoom::registe(Participant * p)                {                    if(!participants.count(p))                    {                        participants.insert(pair<Participant *,string>(p,p->getName()));                    }                    p->setChatRoom(this);                }                void ChatRoom::send(string from,string to ,string message)                {                    map<Participant *,string>::iterator iter;                    for(iter=participants.begin();iter!=participants.end();iter++)                    {                        if(iter->second==to)                                break;                    }                    if(iter!=participants.end())                    {                        iter->first->receive(from,message);                    }                }class Beatle:public Participant{        public:                Beatle(string n=""):Participant(n)                {                }                void receive(string from,string message)                {                    cout<<"to a beatle : ";                    Participant::receive(from,message);                }};class NonBeatle:public Participant{        public:                NonBeatle(string n=""):Participant(n)                {                }                void receive(string from,string message)                {                    cout<<"to a non-beatle : ";                    Participant::receive(from,message);                }};int main(){    cout<<"聊天室中介者模式代码"<<endl;    ChatRoom * chatRoom=new ChatRoom();    Participant *george=new Beatle("George");    Participant *paul=new Beatle("Paul");    Participant *ringo=new Beatle("Ringo");    Participant *john=new Beatle("John");    Participant *yoko=new NonBeatle("Yoko");    chatRoom->registe(george);    chatRoom->registe(paul);    chatRoom->registe(ringo);    chatRoom->registe(john);    chatRoom->registe(yoko);    yoko->send("John","hi John!");    paul->send("Ringo","All you need is love");    ringo->send("George","My sweet Lord");    paul->send("John","can not buy me love");    john->send("Yoko","My sweet love");    return 0;}

执行输出：