一. 概述
- 中介者模式(Mediator Pattern),用一箇中介對象來封裝一系列的對象交互。中介者使各個對象不需要顯式地相互引用,從而使其耦合鬆散,而且可以獨立地改變它們之間的交互。
- 中介者模式屬於行爲型模式,使代碼易於維護。
- 比如MVC模式,C(Controller控制器)是M(Model模型)和V(View視圖)的中介者,在前後端交互時起到了中間人的作用。
- 原理類圖:
- Mediator 就是抽象中介者,定義了同事對象到中介者對象的接口
- Colleague 是抽象同事類
- ConcreteMediator 具體的中介者對象, 實現抽象方法, 他需要知道所有的具體的同事類,即以一個集合來管理HashMap。
- ConcreteColleague 具體的同事類,會有很多,每個同事只知道自己的行爲,而不瞭解其他同事類的行爲,但是他們都依賴中介者對象。
二. 場景示例
- 智能家庭項目
- 智能家庭包括各種設備,鬧鐘、咖啡機、電視機、窗簾 等
- 主人要看電視時,各個設備可以協同工作,自動完成看電視的準備工作,比如流
程爲:鬧鈴響起->咖啡機開始做咖啡->窗簾自動落下->電視機開始播放。
-
思路分析類圖:
-
代碼實現:
public abstract class Mediator {
//將給中介者對象,加入到集合中
public abstract void Register(String colleagueName, Colleague colleague);
//接收消息, 具體的同事對象發出
public abstract void GetMessage(int stateChange, String colleagueName);
public abstract void SendMessage();
}
//同事抽象類
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);
}
import java.util.HashMap;
//具體的中介者類
public class ConcreteMediator extends Mediator {
//集合,放入所有的同事對象
private HashMap<String, Colleague> colleagueMap;
private HashMap<String, String> interMap;
public ConcreteMediator() {
colleagueMap = new HashMap<>();
interMap = new HashMap<>();
}
@Override
public void Register(String colleagueName, Colleague colleague) {
colleagueMap.put(colleagueName, colleague);
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);
}
}
//具體中介者的核心方法
//1. 根據得到消息,完成對應任務
//2. 中介者在這個方法,協調各個具體的同事對象,完成任務
@Override
public void GetMessage(int stateChange, String colleagueName) {
//處理鬧鐘發出的消息
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) {//如果TV發現消息
} else if (colleagueMap.get(colleagueName) instanceof Curtains) {
//如果是以窗簾發出的消息,這裏處理...
}
}
@Override
public void SendMessage() {
}
}
//具體的同事類
public class Alarm extends Colleague {
//構造器
public Alarm(Mediator mediator, String name) {
super(mediator, name);
//在創建Alarm 同事對象時,將自己放入到ConcreteMediator 對象中[集合]
mediator.Register(name, this);
}
public void SendAlarm(int stateChange) {
SendMessage(stateChange);
}
@Override
public void SendMessage(int stateChange) {
//調用的中介者對象的getMessage
this.GetMediator().GetMessage(stateChange, this.name);
}
}
public class CoffeeMachine extends Colleague {
public CoffeeMachine(Mediator mediator, String name) {
super(mediator, name);
mediator.Register(name, this);
}
@Override
public void SendMessage(int stateChange) {
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 Curtains extends Colleague {
public Curtains(Mediator mediator, String name) {
super(mediator, name);
mediator.Register(name, this);
}
@Override
public void SendMessage(int stateChange) {
this.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);
mediator.Register(name, this);
}
@Override
public void SendMessage(int stateChange) {
this.GetMediator().GetMessage(stateChange, this.name);
}
public void StartTv() {
System.out.println("It's time to StartTv!");
}
public void StopTv() {
System.out.println("StopTv!");
}
}
public class ClientTest {
public static void main(String[] args) {
//創建一箇中介者對象
Mediator mediator = new ConcreteMediator();
//創建Alarm 並且加入到 ConcreteMediator 對象的HashMap
Alarm alarm = new Alarm(mediator, "alarm");
//創建了CoffeeMachine 對象,並 且加入到 ConcreteMediator 對象的HashMap
CoffeeMachine coffeeMachine = new CoffeeMachine(mediator,
"coffeeMachine");
//創建 Curtains , 並 且加入到 ConcreteMediator 對象的HashMap
Curtains curtains = new Curtains(mediator, "curtains");
TV tV = new TV(mediator, "TV");
//讓鬧鐘發出消息
alarm.SendAlarm(0);
coffeeMachine.FinishCoffee();
alarm.SendAlarm(1);
}
}
// 輸出
It's time to startcoffee!
It's time to StartTv!
After 5 minutes!
Coffee is ok!
I am holding Up Curtains!
StopTv!
三. 中介者模式的注意事項和細節
- 多個類相互耦合,會形成網狀結構, 使用中介者模式將網狀結構分離爲星型結構,進行解耦。
- 減少類間依賴,降低了耦合,符合迪米特原則。
- 中介者承擔了較多的責任,一旦中介者出現了問題,整個系統就會受到影響。
- 如果設計不當,中介者對象本身變得過於複雜,這點在實際使用時,要特別注意。