## 5. 中介者（Mediator）
### Intent
集中相关对象之间复杂的沟通和控制方式。
### 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
### 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：
```java
public abstract class Colleague {
public abstract void onEvent(Mediator mediator);
}
```
```java
public class Alarm extends Colleague {
@Override
public void onEvent(Mediator mediator) {
mediator.doEvent("alarm");
}
public void doAlarm() {
System.out.println("doAlarm()");
}
}
```
```java
public class CoffeePot extends Colleague {
@Override
public void onEvent(Mediator mediator) {
mediator.doEvent("coffeePot");
}
public void doCoffeePot() {
System.out.println("doCoffeePot()");
}
}
```
```java
public class Calender extends Colleague {
@Override
public void onEvent(Mediator mediator) {
mediator.doEvent("calender");
}
public void doCalender() {
System.out.println("doCalender()");
}
}
```
```java
public class Sprinkler extends Colleague {
@Override
public void onEvent(Mediator mediator) {
mediator.doEvent("sprinkler");
}
public void doSprinkler() {
System.out.println("doSprinkler()");
}
}
```
```java
public abstract class Mediator {
public abstract void doEvent(String eventType);
}
```
```java
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() {
// ...
}
}
```
```java
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);
}
}
```
```java
doAlarm()
doCoffeePot()
doCalender()
doSprinkler()
```
### JDK
- All scheduleXXX() methods of [java.util.Timer](http://docs.oracle.com/javase/8/docs/api/java/util/Timer.html)
- [java.util.concurrent.Executor#execute()](http://docs.oracle.com/javase/8/docs/api/java/util/concurrent/Executor.html#execute-java.lang.Runnable-)
- submit() and invokeXXX() methods of [java.util.concurrent.ExecutorService](http://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ExecutorService.html)
- scheduleXXX() methods of [java.util.concurrent.ScheduledExecutorService](http://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ScheduledExecutorService.html)
- [java.lang.reflect.Method#invoke()](http://docs.oracle.com/javase/8/docs/api/java/lang/reflect/Method.html#invoke-java.lang.Object-java.lang.Object...-)
