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Mediator Pattern 物件行為型模式
意圖
用一個中介物件來封裝一系列的物件互動。中介者使各物件不需要顯式地相互參照，從而使其耦合鬆散，而且可以獨立地改變它們之間的互動。
結構
其中：
- Mediator (中介者) 定義一個介面用於各同事 (Colleague) 物件通訊。
- ConcreteMediator (具體中介者) 透過協調各同事物件實現協作行為；了解並維護它的各個同事。
- Colleague class (同事類別) 知道它的中介者物件；每一個同事類別物件在需要與其他同事通訊的時候與它的中介者通訊。
適用性
Mediator 模式適用於：
- 一組物件以定義良好但複雜的方式進行通訊，產生的相互依賴關係結構混亂且難以理解。
- 一個物件參照其他很多物件並且直接與這些物件通訊，導致難以重複使用該物件。
- 想客製化一個分布在多個類別中的行為，而又不想產生過多的子類別。
範例 1
線上支付是電子商務的一個重要環節，不同的電子商務平台提供了不同的支付介面。現在需要整合不同電子商務平台的支付介面，使得客戶在不同平台上購物時，不需要關心具體的支付介面。擬採用中介者 (Mediator) 設計模式來實現該需求，類別圖如下所示：
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| interface WebServiceMediator {
public void buy(double money, WebService service);
public void SetAmazon(WebService amazon);
public void SetEbay(WebService ebay);
}
abstract class WebService {
protected WebServiceMediator mediator;
public abstract void SetMediator(WebServiceMediator mediator);
public abstract void buyService(double money);
public abstract void search(double money);
}
class ConcreteServiceMediator implements WebServiceMediator {
private WebService amazon;
private WebService ebay;
public ConcreteServiceMediator() {
amazon = null;
ebay = null;
}
public void SetAmazon(WebService amazon) {
this.amazon = amazon;
}
public void SetEbay(WebService ebay) {
this.ebay = ebay;
}
public void buy(double money, WebService service) {
if (service == amazon)
amazon.search(money);
else
ebay.search(money);
}
}
class Amazon extends WebService {
public void SetMediator(WebServiceMediator mediator) {
this.mediator = mediator;
}
public void buyService(double money) {
mediator.buy(money, this);
}
public void search(double money) {
System.out.println("Amazon receive：" + money);
}
}
class Ebay extends WebService {
public void SetMediator(WebServiceMediator mediator) {
this.mediator = mediator;
}
public void buyService(double money) {
mediator.buy(money, this);
}
public void search(double money) {
System.out.println("Ebay receive：" + money);
}
}
|
範例 2
兩個同事之間通訊
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| public class MediatorPattern {
public static void main(String[] args) {
ConcreteMediator m = new ConcreteMediator();
Colleague1 c1 = new Colleague1(m);
Colleague2 c2 = new Colleague2(m);
m.setC1(c1);
m.setC2(c2);
c1.sendMessage("hello");
c2.sendMessage("hi");
}
}
abstract class Colleague{
protected Mediator mediator;
}
class Colleague1 extends Colleague{
public Colleague1(Mediator mediator){
this.mediator = mediator;
}
public void sendMessage(String message){
mediator.sendMessage(message, this);
}
public void Notify(String message){
System.out.println("Colleague1 received: " + message);
}
}
class Colleague2 extends Colleague{
public Colleague2(Mediator mediator){
this.mediator = mediator;
}
public void sendMessage(String message){
mediator.sendMessage(message, this);
}
public void Notify(String message){
System.out.println("Colleague2 received: " + message);
}
}
abstract class Mediator{
public abstract void sendMessage(String message, Colleague c);
}
class ConcreteMediator extends Mediator{
// 因為此範例物件很少，所以直接定義
private Colleague1 c1;
private Colleague2 c2;
// 如果同事很多
// List<Colleague> list = new ArrayList<>();
// public void Add(Colleague c){
// list.add(c);
// }
public void setC1(Colleague1 c1){
this.c1 = c1;
}
public void setC2(Colleague2 c2){
this.c2 = c2;
}
@Override
public void sendMessage(String message, Colleague c){
if(c == c1){
// 讓同事 2 收到消息
c2.Notify(message);
}else{
// 讓同事 1 收到消息
c1.Notify(message);
}
}
}
|