设计模式 - 中介者.md

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：

publicabstractclassColleague { publicabstractvoidonEvent(Mediatormediator); }

publicclassAlarmextendsColleague { @OverridepublicvoidonEvent(Mediatormediator) { mediator.doEvent("alarm"); } publicvoiddoAlarm() { System.out.println("doAlarm()"); } }

publicclassCoffeePotextendsColleague { @OverridepublicvoidonEvent(Mediatormediator) { mediator.doEvent("coffeePot"); } publicvoiddoCoffeePot() { System.out.println("doCoffeePot()"); } }

publicclassCalenderextendsColleague { @OverridepublicvoidonEvent(Mediatormediator) { mediator.doEvent("calender"); } publicvoiddoCalender() { System.out.println("doCalender()"); } }

publicclassSprinklerextendsColleague { @OverridepublicvoidonEvent(Mediatormediator) { mediator.doEvent("sprinkler"); } publicvoiddoSprinkler() { System.out.println("doSprinkler()"); } }

publicabstractclassMediator { publicabstractvoiddoEvent(StringeventType); }

publicclassConcreteMediatorextendsMediator { privateAlarmalarm; privateCoffeePotcoffeePot; privateCalendercalender; privateSprinklersprinkler; publicConcreteMediator(Alarmalarm, CoffeePotcoffeePot, Calendercalender, Sprinklersprinkler) { this.alarm = alarm; this.coffeePot = coffeePot; this.calender = calender; this.sprinkler = sprinkler; } @OverridepublicvoiddoEvent(StringeventType) { switch (eventType) { case"alarm": doAlarmEvent(); break; case"coffeePot": doCoffeePotEvent(); break; case"calender": doCalenderEvent(); break; default: doSprinklerEvent(); } } publicvoiddoAlarmEvent() { alarm.doAlarm(); coffeePot.doCoffeePot(); calender.doCalender(); sprinkler.doSprinkler(); } publicvoiddoCoffeePotEvent() { // ... } publicvoiddoCalenderEvent() { // ... } publicvoiddoSprinklerEvent() { // ... } }

publicclassClient { publicstaticvoidmain(String[] args) { Alarmalarm = newAlarm(); CoffeePotcoffeePot = newCoffeePot(); Calendercalender = newCalender(); Sprinklersprinkler = newSprinkler(); Mediatormediator = newConcreteMediator(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); } }

doAlarm() doCoffeePot() doCalender() doSprinkler()

JDK

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