java 开发模式之二十 :中介者模式
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原理或定義
用一个中介者对象来封装一系列的对象交互。中介者使得各对象不需要显式地相互引用,从而使其松散耦合,而且可以独立地改变它们之间的交互。
结构
Mediator:中介者接口。在里面定义了各个同事之间相互交互所需要的方法,可以是公共的方法,如Change方法,也可以是小范围的交互方法。
ConcreteMediator:具体的中介者实现对象。它需要了解并为维护每个同事对象,并负责具体的协调各个同事对象的交互关系。
Colleague:同事类的定义,通常实现成为抽象类,主要负责约束同事对象的类型,并实现一些具体同事类之间的公共功能,比如,每个具体同事类都应该知道中介者对象,也就是每个同事对象都会持有中介者对象的引用,这个功能可定义在这个类中。
ConcreteColleague:具体的同事类,实现自己的业务,需要与其他同事对象交互时,就通知中介对象,中介对象会负责后续的交互
類圖
案例与代码
本文使用智慧房屋项目作为示例
描述:早上8点或设定的时间,家里的设备会自动开始按顺序工作。
智慧房屋公司的产品:
闹钟、咖啡机、电视机、窗帘等
中介者模式的设计方案:
Colleague:
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);}
ConcreteColleague:
public class Alarm extends Colleague {public Alarm(Mediator mediator, String name) {super(mediator, name);// TODO Auto-generated constructor stubmediator.Register(name, this);}public void SendAlarm(int stateChange) {SendMessage(stateChange);}@Overridepublic void SendMessage(int stateChange) {// TODO Auto-generated method stubthis.GetMediator().GetMessage(stateChange, this.name);}}
public class CoffeeMachine extends Colleague {public CoffeeMachine(Mediator mediator, String name) {super(mediator, name);// TODO Auto-generated constructor stubmediator.Register(name, this);}@Overridepublic void SendMessage(int stateChange) {// TODO Auto-generated method stubthis.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 Curtains extends Colleague {public Curtains(Mediator mediator, String name) {super(mediator, name);// TODO Auto-generated constructor stubmediator.Register(name, this);}@Overridepublic void SendMessage(int stateChange) {// TODO Auto-generated method stubthis.GetMediator().GetMessage(stateChange, this.name);}public void UpCurtains() {System.out.println("I am holding Up Curtains!");}}
public class TV extends Colleague {public TV(Mediator mediator, String name) {super(mediator, name);// TODO Auto-generated constructor stubmediator.Register(name, this);}@Overridepublic void SendMessage(int stateChange) {// TODO Auto-generated method stubthis.GetMediator().GetMessage(stateChange, this.name);}public void StartTv() {// TODO Auto-generated method stubSystem.out.println("It's time to StartTv!");}public void StopTv() {// TODO Auto-generated method stubSystem.out.println("StopTv!");}}
Mediator:
public interface Mediator {public abstract void Register(String colleagueName, Colleague colleague);public abstract void GetMessage(int stateChange, String colleagueName);public abstract void SendMessage();}
ConcreteColleague:
public class ConcreteMediator implements Mediator {private HashMap<String, Colleague> colleagueMap;private HashMap<String, String> interMap;public ConcreteMediator() {colleagueMap = new HashMap<String, Colleague>();interMap = new HashMap<String, String>();}@Overridepublic void Register(String colleagueName, Colleague colleague) {// TODO Auto-generated method stubcolleagueMap.put(colleagueName, colleague);// TODO Auto-generated method stubif (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);}}@Overridepublic void GetMessage(int stateChange, String colleagueName) {// TODO Auto-generated method stubif (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) {}}@Overridepublic void SendMessage() {// TODO Auto-generated method stub}}
管理/ 测试类:
public class MainTest {public static void main(String[] args) {Mediator mediator = new ConcreteMediator();Alarm mAlarm = new Alarm(mediator, "mAlarm");CoffeeMachine mCoffeeMachine = new CoffeeMachine(mediator,"mCoffeeMachine");Curtains mCurtains = new Curtains(mediator, "mCurtains");TV mTV = new TV(mediator, "mTV");mAlarm.SendAlarm(0);mCoffeeMachine.FinishCoffee();mAlarm.SendAlarm(1);}}
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
使用場景
1. 一般来说,只有对于那种同事类之间是网状结构的关系,才会考虑使用中介者模式;
2. 系统中对象之间存在比较复杂的引用关系,导致他们之间的依赖关系结构混乱而且难以复用该对象。
3. 想通过一个中间类来封装多个类中的行为,而又不想生成太多的子类。
優缺點
主要优点有:
1. 适当地使用中介者模式可以避免同事类之间的过度耦合,使得各同事类之间可以相对独立地使用。
2.可以将对象间一对多的关联转变为一对一,使对象间的关系易于理解和维护。
3.可以将对象的行为和协作进行抽象,能够比较灵活的处理对象间的相互作用
缺点主要有:
中介者模式的缺点是显而易见的,因为这个“中介“承担了较多的责任,所以一旦这个中介对象出现了问题,那么整个系统就会受到重大的影响。
如果设计不当,中介者对象本身变得过于复杂