中介者模式

根据面向对象的七大设计原则中的迪米特原则，也就是最少知道原则实现低耦合高内聚的设计思想，将对象之间的交互隔离开来，但不缺乏功能的完整性，这就是中介者模式的核心思想，简单来说就是其他所有需要交互的对象都与中介者对象相关联，通过中介者的操作实现对象间的交互

Meditor.java

public abstract class Mediator {
    public abstract void send(String msg, WeChat weChat);
}

SpecificMeditor.java

public class SpecificMediator extends Mediator {

    private A a;
    private B b;

    public A getA() {
        return a;
    }

    public void setA(A a) {
        this.a = a;
    }

    public B getB() {
        return b;
    }

    public void setB(B b) {
        this.b = b;
    }

    @Override
    public void send(String msg, WeChat weChat) {
        if (weChat == a){
            b.notify(msg);
        }
        else {
            a.notify(msg);
        }
    }
}

WeChat.java

public abstract class WeChat {

    private Mediator mediator;

    public WeChat(Mediator mediator) {
        this.mediator = mediator;
    }
}

A.java

public class A extends WeChat {

    private Mediator mediator;

    public A(Mediator mediator) {
        super(mediator);
        this.mediator = mediator;
    }

    public void send(String msg){
        mediator.send(msg, this);
    }

    public void notify(String msg){
        System.out.println("B-->A A收到msg:"+msg);
    }
}

B.java

public class B extends WeChat {

    private Mediator mediator;

    public B(Mediator mediator) {
        super(mediator);
        this.mediator = mediator;
    }

    public void send(String msg){
        mediator.send(msg, this);
    }

    public void notify(String msg){
        System.out.println("A-->B B收到msg:"+msg);
    }
}

TestMeditor.java

public class TestMediator {
    public static void main(String[] args) {
        SpecificMediator mediator = new SpecificMediator();
        A a = new A(mediator);
        B b = new B(mediator);
        mediator.setA(a);
        mediator.setB(b);
        a.send("天王盖地虎");
        b.send("小鸡炖蘑菇");
    }
}

Run result

A-->B B收到msg:天王盖地虎
B-->A A收到msg:小鸡炖蘑菇

从这个例子可以看出消息实际上都是通过mediator来实现交互的，只不过需要再创建交互对象的时候需要“认识”mediator即可，这种行为型模式也有缺点，中介者需要认识所有对象，使得其组织变得难以维护，而且不能在职责混乱的时候使用