重温设计模式之中介者模式

中介者模式  Mediator Pattern

用一个中介对象来封装一系列的对象交互，中介者使各对象不需要显式地相互引用，从而使其耦合松散，而且可以独立地改变它们之间的交互。

生活中我们经常会需要中介，比如租房找房产中介要比自己找要方便的多。

再如订外卖，如果没有外卖平台，就要保存很多的外卖菜单，即使这样也会因为消息不及时而错过一些新店开业的优惠。而对餐馆来说，想加几样新菜要么是等别人订餐时挨个推销，要么去街头发新的菜单。

在有个了中介-外卖平台以后，这些就变得简单多了，顾客和餐馆都只需要知道中介就可以了，彼此之间不需要关联。

UML图：

代码：

public abstract class Colleague { protected Mediator mediator; public Colleague(Mediator mediator) { this.mediator = mediator; } public abstract void send(String message); public abstract void receive(String message, String from); }

 

public class Customer extends Colleague { public Customer(Mediator mediator) { super(mediator); } @Override public void send(String message) { System.out.println("Customer发出消息: " + message); this.mediator.send(message, "Customer"); } @Override public void receive(String message, String from) { System.out.println("Customer收到来自" + from + "的消息: " + message); } } public class Restaurant extends Colleague { public Restaurant(Mediator mediator) { super(mediator); } @Override public void send(String message) { System.out.println("Restaurant发出消息: " + message); this.mediator.send(message, "Restaurant"); } @Override public void receive(String message, String from) { System.out.println("Restaurant收到来自" + from + "的消息: " + message); } } public class DeliveryMan extends Colleague { public DeliveryMan(Mediator mediator) { super(mediator); } @Override public void send(String message) { System.out.println("DeliveryMan发出消息: " + message); this.mediator.send(message, "DeliveryMan"); } @Override public void receive(String message, String from) { System.out.println("DeliveryMan收到来自" + from + "的消息: " + message); } } public abstract class Mediator { public abstract void send(String message, String from); } public class MeituanMediator extends Mediator { private Colleague customer; private Colleague restaurant; private Colleague deliveryMan; @Override public void send(String message, String from) { switch (from) { case "Customer": restaurant.receive(message, from); break; case "Restaurant": deliveryMan.receive(message, from); break; case "DeliveryMan": customer.receive(message, from); break; } } public void setCustomer(Colleague customer) { this.customer = customer; } public void setRestaurant(Colleague restaurant) { this.restaurant = restaurant; } public void setDeliveryMan(Colleague deliveryMan) { this.deliveryMan = deliveryMan; } }

客户端： 

public class Client { public static void main(String[] args) { MeituanMediator meituanMediator = new MeituanMediator(); Colleague customer = new Customer(meituanMediator); Colleague restaurant = new Restaurant(meituanMediator); Colleague deliveryMan = new DeliveryMan(meituanMediator); meituanMediator.setCustomer(customer); meituanMediator.setRestaurant(restaurant); meituanMediator.setDeliveryMan(deliveryMan); customer.send("订一份披萨"); restaurant.send("披萨打包完毕"); deliveryMan.send("30分钟后送到"); } } Customer发出消息: 订一份披萨 Restaurant收到来自Customer的消息: 订一份披萨 Restaurant发出消息: 披萨打包完毕 DeliveryMan收到来自Restaurant的消息: 披萨打包完毕 DeliveryMan发出消息: 30分钟后送到 Customer收到来自DeliveryMan的消息: 30分钟后送到