1.定义

GOF的定义
Define an object that encapsulates how a set of objects interact. Mediator promotes loose coupling by keeping objects from referring to each other explicitly, and it lets you vary their interaction independently.
定义一个对象，这个对象封装了一组对象的交互。 中介者模式通过使各个对象之间不用显示交互，来解耦各个对象，并且 中介者 模式允许 对象独立的改变他的交互。

光看定义，不好理解，直接上图，就秒懂。

假设有如下5个对象，对象之间的交互关系如下

对象的交互错综复杂，难以维护

下图， 引入了中介者， 对象间的交互， 全部甩给中介者负责。
对象间的交互关系变得清晰好维护。

2.实现

以 聊天室 为例， 聊天室 作为 Mediator， 负责 用户 之间的交互。
用户不用关心彼此之间怎么交互，典型的 中介模式。

加入 聊天室 的用户，能收到其他用户的 消息， 但是 用户自己不用收到自己的消息。
假设有5个用户user1，user2，user3，user4，user5。
user1, user2, 加入 聊天室 chat1
user3, user4, user5 加入 聊天室 chat2

下面用代码实现该场景

2.1 cpp实现

为了养成好习惯，后续博客的cpp示例代码都区分了值语义和对象语义， 且使用了 c++11 的 智能指针

//sbkun
#include "noncopyable.h"#include <iostream>
#include <map>
#include <string>
#include <memory>using namespace std;
class ChatRoom;class User: noncopyable {public:User(const string& name);~User() {cout<<this<<" "<<name_<<" destruct"<<endl;}void send(const string& msg);void recv(const string& msg);void setRoom(weak_ptr<ChatRoom> room) {room_ = room;}const string& getName() const {return name_;}private:string name_;weak_ptr<ChatRoom> room_;
};//mediator
class ChatRoom : noncopyable, public enable_shared_from_this<ChatRoom>{public:typedef map<string, weak_ptr<User>> Room;ChatRoom(const string& name) : name_(name) {}~ChatRoom() {cout<<this<<" "<<name_<<" destruct"<<endl;}void addRoom(shared_ptr<User> user) {room_[user->getName()] = user;user->setRoom(shared_from_this());}void send( const string& msg, const string& userName) {for(auto const& it: room_) {auto pUser = it.second.lock();if (pUser) {//自己不用收自己的消息	if (pUser->getName() != userName) {pUser->recv(msg);}}}}const string& getName() const {return name_;}private:Room room_;string name_;
};User::User(const string& name) : name_(name)
{
}void User::send(const string& msg) {shared_ptr<ChatRoom> pRoom = room_.lock();if (pRoom) {cout<<name_<<" send "<<msg<<" to "<<pRoom->getName()<<endl;pRoom->send(msg, name_);}
}void User::recv(const string& msg) {shared_ptr<ChatRoom> pRoom = room_.lock();if (pRoom) {cout<<getName()<<" recv "<<msg<<" from "<<pRoom->getName()<<endl;}
}int main(int argc, char* argv[])
{auto chat1 = make_shared<ChatRoom>("chat1");auto chat2 = make_shared<ChatRoom>("chat2");auto user1 = make_shared<User>("user1");auto user2 = make_shared<User>("user2");auto user3 = make_shared<User>("user3");auto user4 = make_shared<User>("user4");auto user5 = make_shared<User>("user5");chat1->addRoom(user1);chat1->addRoom(user2);chat2->addRoom(user3);chat2->addRoom(user4);chat2->addRoom(user5);user1->send("sbkun");cout<<endl;user3->send("sbkun");cout<<endl;return 0;
}

输出

[sbkun:designpattern]$ ./mediatordemo
user1 send sbkun to chat1
user2 recv sbkun from chat1user3 send sbkun to chat2
user4 recv sbkun from chat2
user5 recv sbkun from chat2

2.2 java实现

//sbkun
package designpattern.mediator;import java.util.HashMap;
import java.util.Map;class ChatRoom {ChatRoom(String name) {this.name = name;}void addRoot(User user) {room.put(user.getName(), user);user.setRoom(this);}void send(String msg, String userName) {for(Map.Entry<String, User> entry: room.entrySet()) {if (!entry.getKey().equals(userName)) {User user = entry.getValue();user.recv(msg);}}}public String getName() {return name;}private String name;private Map<String, User> room = new HashMap<String, User>();
}class User {User(String name) {this.name = name;}void send(String msg) {if (room != null) {System.out.println(name + " send " + msg + " to " + room.getName());room.send(msg, name);}}void recv(String msg) {if (room != null) {System.out.println(name + " recv " + msg + " from " + room.getName());}}public String getName() {return name;}public void setRoom(ChatRoom room) {this.room = room;}private String name;private ChatRoom room = null;
}public class MediatorDemo {static public void main(String args[]) {ChatRoom chat1 = new ChatRoom("chat1");ChatRoom chat2 = new ChatRoom("chat2");User user1 = new User("user1");User user2 = new User("user2");User user3 = new User("user3");User user4 = new User("user4");User user5 = new User("user5");chat1.addRoot(user1);chat1.addRoot(user2);chat2.addRoot(user3);chat2.addRoot(user4);chat2.addRoot(user5);user1.send("sbkun");System.out.println("");user3.send("sbkun");}
}

4. 完整代码地址

该专栏的所有代码都已上传到github, 希望大家能多多批评指正
[git链接](https://github.com/uyghfjhh/designpattern.git