设计模式-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。 中介者使各个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； 中介者模式属于行为型模式，使代码易于维护； 比如MVC模式，C（Controller控制器）是M（Model模型）和V（View视图）的中 介者，在前后端交互时起到了中间人的作用。

1.类图

2.代码

//同事抽象类 mediator
public abstract class Colleague {
   private Mediator mediator;
   public String name;

   public Colleague(Mediator mediator, String name) {

      this.mediator = mediator;
      this.name = name;

   }

   public Mediator GetMediator() {
      return this.mediator;
   }

   public abstract void SendMessage(int stateChange);
}

public class CoffeeMachine extends Colleague {

   public CoffeeMachine(Mediator mediator, String name) {
      super(mediator, name);
      // TODO Auto-generated constructor stub
      mediator.Register(name, this);
   }

   @Override
   public void SendMessage(int stateChange) {
      // TODO Auto-generated method stub
      this.GetMediator().GetMessage(stateChange, this.name);
   }

   public void StartCoffee() {
      System.out.println("It's time to startcoffee!");
   }

   public void FinishCoffee() {

      System.out.println("After 5 minutes!");
      System.out.println("Coffee is ok!");
      SendMessage(0);
   }
}

public class Alarm extends Colleague {

   public Alarm(Mediator mediator, String name) {
      super(mediator, name);
      // TODO Auto-generated constructor stub
      //创建Alarm同事类时将自己放入（注册）ConcreteMediator
      mediator.Register(name, this);
   }

   public void SendAlarm(int stateChange) {
      SendMessage(stateChange);
   }

   @Override
   public void SendMessage(int stateChange) {
      // TODO Auto-generated method stub
      //调用中介者对象的getMessage
      this.GetMediator().GetMessage(stateChange, this.name);
   }

}

//中介者
public abstract class Mediator {
   //注册同事
   public abstract void Register(String colleagueName, Colleague colleague);
   //接受消息 具体同事对象发出
   public abstract void GetMessage(int stateChange, String colleagueName);

   public abstract void SendMessage();
}

//具体中介者
public class ConcreteMediator extends Mediator {

   //所有同事对象
   private HashMap<String, Colleague> colleagueMap;
   private HashMap<String, String> interMap;

   public ConcreteMediator() {
      colleagueMap = new HashMap<String, Colleague>();
      interMap = new HashMap<String, String>();
   }

   //注册各个同事到中介者
   @Override
   public void Register(String colleagueName, Colleague colleague) {
      // TODO Auto-generated method stub
      colleagueMap.put(colleagueName, colleague);

      // TODO Auto-generated method stub

      if (colleague instanceof Alarm) {
         interMap.put("Alarm", colleagueName);
      } else if (colleague instanceof CoffeeMachine) {
         interMap.put("CoffeeMachine", colleagueName);
      } else if (colleague instanceof TV) {
         interMap.put("TV", colleagueName);
      } else if (colleague instanceof Curtains) {
         interMap.put("Curtains", colleagueName);
      }

   }


   //根据得到的消息完成对应的任务  中介者在这个方法中协调各个同事对象
   @Override
   public void GetMessage(int stateChange, String colleagueName) {
      if (colleagueMap.get(colleagueName) instanceof Alarm) {
         if (stateChange == 0) {
            ((CoffeeMachine) (colleagueMap.get(interMap
                  .get("CoffeeMachine")))).StartCoffee();
            ((TV) (colleagueMap.get(interMap.get("TV")))).StartTv();
         } else if (stateChange == 1) {
            ((TV) (colleagueMap.get(interMap.get("TV")))).StopTv();
         }

      } else if (colleagueMap.get(colleagueName) instanceof CoffeeMachine) {
         ((Curtains) (colleagueMap.get(interMap.get("Curtains"))))
               .UpCurtains();

      } else if (colleagueMap.get(colleagueName) instanceof TV) {

      } else if (colleagueMap.get(colleagueName) instanceof Curtains) {

      }
   }

   @Override
   public void SendMessage() {
      // TODO Auto-generated method stub
   }
}

public static void main(String[] args) {
   Mediator mediator = new ConcreteMediator();

   Alarm alarm = new Alarm(mediator, "alarm");

   CoffeeMachine coffeeMachine = new CoffeeMachine(mediator,
         "coffeeMachine");

   Curtains curtains = new Curtains(mediator, "curtains");
   TV tV = new TV(mediator, "TV");
  
   alarm.SendAlarm(0);
   coffeeMachine.FinishCoffee();
   alarm.SendAlarm(1);
}

中介者模式的注意事项和细节

1. 多个类相互耦合，会形成网状结构, 使用中介者模式将网状结构分离为星型结构， 进行解耦

2. 减少类间依赖，降低了耦合，符合迪米特原则

3. 中介者承担了较多的责任，一旦中介者出现了问题，整个系统就会受到影响

4. 如果设计不当，中介者对象本身变得过于复杂，这点在实际使用时，要特别注意