设计模式读书笔记之中介者模式(mediator pattern)

中介者模式：用一个中介对象来分装一系列对象的交互。中介者模式使得各个对象之间不需要直接打交道，从而使他们松散耦合。可以独立的改变他们之间的交互。

如果你第一次接触中介者模式，你一定从上图看不出他的作用来。下图更能说明问题, 中介者模式就是要把左边的结构变成右边的结构：

现实中一个更恰当的例子就是联合国，如果没有联合国，则各国之间的关系如下图的左边，在有联合国之后，国与国之间的争执可通过联合国来处理。

基础代码：

// package designpattern.mediator; public interface Mediator { public void send(String msg, Colleague c); } // package designpattern.mediator; abstract public class Colleague { protected Mediator mediator; public Colleague(Mediator m){ this.mediator = m; } public abstract void send(String msg); public abstract void readMsg(String msg); } // package designpattern.mediator; public class ConcreteMediator implements Mediator { private ConcreteColleague1 colleague1; private ConcreteColleague2 colleague2; public void setColleague1(ConcreteColleague1 colleague1) { this.colleague1 = colleague1; } public void setColleague2(ConcreteColleague2 colleague2) { this.colleague2 = colleague2; } public void send(String msg, Colleague c) { if(c==colleague1){ colleague2.readMsg(msg); } else{ colleague1.readMsg(msg); } } } // package designpattern.mediator; public class ConcreteColleague1 extends Colleague{ public ConcreteColleague1(Mediator m) { super(m); } public void send(String msg){ System.out.println("Colleague1 sends msg: " + msg); mediator.send(msg, this); } public void readMsg(String msg){ System.out.println("Colleague1 get msg: " + msg); } } // package designpattern.mediator; public class ConcreteColleague2 extends Colleague{ public ConcreteColleague2(Mediator m) { super(m); } public void send(String msg){ System.out.println("Colleague2 sends msg: " + msg); mediator.send(msg, this); } public void readMsg(String msg){ System.out.println("Colleague2 gets msg: " + msg); } } //测试用例 package designpattern.mediator; public class Test { public static void main(String[] args) { ConcreteMediator mediator = new ConcreteMediator(); ConcreteColleague1 c1 = new ConcreteColleague1(mediator); ConcreteColleague2 c2 = new ConcreteColleague2(mediator); mediator.setColleague1(c1); mediator.setColleague2(c2); c1.send("吃了吗？"); c2.send("没有， 你要请客吗？"); } }

优点：把中介者作为一个独立的概念，可使对象之间的关系转为对象和中介者之间的关系， 可站在一个宏观的角度看问题。

缺点：中介者集中控制关系，使得中介者变得复杂。