中介者（Mediator）

1. 意图（Intent）

集中相关对象之间复杂的沟通和控制方式。

2. 类图（Class Diagram）

• Mediator ：中介者，定义一个接口用于与各同事（Colleague）对象通信。
• Colleague：同事，相关对象

  3. 实现（Implementation）

Alarm（闹钟）、CoffeePot（咖啡壶）、Calendar（日历）、Sprinkler（喷头）是一组相关的对象，在某个对象的事件产生时需要去操作其它对象，形成了下面这种依赖结构：

使用中介者模式可以将复杂的依赖结构变成星形结构：

抽象的相关对象类 [ Colleague ]

public abstract class Colleague {
    public abstract void onEvent(Mediator mediator);
}

[ ConcreteColleague ]
具体的相关对象警报实现类

public class Alarm extends Colleague {
    @Override
    public void onEvent(Mediator mediator) {
        mediator.doEvent("alarm");
    }
    public void doAlarm() {
        System.out.println("doAlarm()");
    }
}

具体的相关对象咖啡壶实现类

public class CoffeePot extends Colleague {
    @Override
    public void onEvent(Mediator mediator) {
        mediator.doEvent("coffeePot");
    }
    public void doCoffeePot() {
        System.out.println("doCoffeePot()");
    }
}

具体的相关对象日历表实现类

public class Calender extends Colleague {
    @Override
    public void onEvent(Mediator mediator) {
        mediator.doEvent("calender");
    }
    public void doCalender() {
        System.out.println("doCalender()");
    }
}

具体的相关对象洒水壶实现类

public class Sprinkler extends Colleague {
    @Override
    public void onEvent(Mediator mediator) {
        mediator.doEvent("sprinkler");
    }
    public void doSprinkler() {
        System.out.println("doSprinkler()");
    }
}

抽象的中介者类 [ Mediator ]

public abstract class Mediator {
    public abstract void doEvent(String eventType);
}

具体的中介者实现类 [ ConcreteMediator ]

public class ConcreteMediator extends Mediator {
    private Alarm alarm;
    private CoffeePot coffeePot;
    private Calender calender;
    private Sprinkler sprinkler;
    public ConcreteMediator(Alarm alarm, CoffeePot coffeePot, Calender calender, Sprinkler sprinkler) {
        this.alarm = alarm;
        this.coffeePot = coffeePot;
        this.calender = calender;
        this.sprinkler = sprinkler;
    }
    @Override
    public void doEvent(String eventType) {
        switch (eventType) {
            case "alarm":
                doAlarmEvent();
                break;
            case "coffeePot":
                doCoffeePotEvent();
                break;
            case "calender":
                doCalenderEvent();
                break;
            default:
                doSprinklerEvent();
        }
    }
    public void doAlarmEvent() {
        alarm.doAlarm();
        coffeePot.doCoffeePot();
        calender.doCalender();
        sprinkler.doSprinkler();
    }
    public void doCoffeePotEvent() {
        // ...
    }
    public void doCalenderEvent() {
        // ...
    }
    public void doSprinklerEvent() {
        // ...
    }
}

客户端演示代码：

public class Client {
    public static void main(String[] args) {
        Alarm alarm = new Alarm();
        CoffeePot coffeePot = new CoffeePot();
        Calender calender = new Calender();
        Sprinkler sprinkler = new Sprinkler();
        Mediator mediator = new ConcreteMediator(alarm, coffeePot, calender, sprinkler);
        // 闹钟事件到达，调用中介者就可以操作相关对象
        alarm.onEvent(mediator);
    }
}

// 输出:
// doAlarm()
// doCoffeePot()
// doCalender()
// doSprinkler()

4. JDK

• All scheduleXXX() methods of java.util.Timer(opens new window)
• java.util.concurrent.Executor#execute()(opens new window)
• submit() and invokeXXX() methods of java.util.concurrent.ExecutorService(opens new window)
• scheduleXXX() methods of java.util.concurrent.ScheduledExecutorService(opens new window)
• java.lang.reflect.Method#invoke()