原文链接：http://www.hechunchen.info/?p=54
生活中的中介者非常常见，比如维护世界和平的联合国组织、房屋中介、出国中介。那么，设计模式中的中介者模式是怎么样的呢？我们openfire中的群组聊天就是a typical example。我们用一个简化的群组聊天模型来说明mediator（中介者）模式。
我们的考虑是这样的，我们在用户之间添加中介者——聊天室。这样的话，用户之间的耦合度就会降低，而且不需要相互引用。它们只需独立地跟中介者交互即可。 结构图如下： 
下面贴上关键代码。 接口IChatroom.java：
package mediator;
public interface IChatroom
{
void forward(User from, User to, String message);
}
Chatroom.java:
package mediator;
public class Chatroom implements IChatroom
{
@Override
public void forward(User from, User to, String message)
{
// TODO Auto-generated method stub
if(to!=null)
{
to.receive(from, message);
}
}
}
抽象类User.java:
package mediator;
public abstract class User
{
IChatroom room;
public User(IChatroom room)
{
this.room = room;
}
public abstract void send(User to, String message);
public abstract void receive(User from, String message);
}
MaleUser.java:
package mediator;
public class MaleUser extends User
{
public MaleUser(IChatroom room)
{
super(room);
// TODO Auto-generated constructor stub
}
@Override
public void receive(User from, String message)
{
// TODO Auto-generated method stub
System.out.println("帅哥我收到了：" + message);
}
@Override
public void send(User to, String message)
{
// TODO Auto-generated method stub
room.forward(this, to, message);
}
}
FemaleUser.java:
package mediator;
public class FemaleUser extends User
{
public FemaleUser(IChatroom room)
{
super(room);
// TODO Auto-generated constructor stub
}
@Override
public void receive(User from, String message)
{
// TODO Auto-generated method stub
System.out.println("美女我收到了：" + message);
}
@Override
public void send(User to, String message)
{
// TODO Auto-generated method stub
room.forward(this, to, message);
}
}
测试类TestClient.java:
package mediator;
public class TestClient
{
/**
* @param args
*/
public static void main(String[] args)
{
// TODO Auto-generated method stub
IChatroom room = new Chatroom();
FemaleUser hcc = new FemaleUser(room);
MaleUser fq = new MaleUser(room);
MaleUser gq = new MaleUser(room);
MaleUser lp = new MaleUser(room);
//男给男发消息
gq.send(fq, "吃饭了没?");
//男给女发消息
lp.send(hcc, "我也没吃饭");
}
}
总结一下，Mediator改变了原来两个对象的耦合方式。