本篇講解Java設(shè)計(jì)模式中的中介模式，分為定義、模式應(yīng)用前案例、結(jié)構(gòu)、模式應(yīng)用后案例、適用場(chǎng)景、模式可能存在的困惑和本質(zhì)探討7個(gè)部分。nvA28資訊網(wǎng)——每日最新資訊28at.com

定義

中介模式是用一個(gè)中介對(duì)象來封裝一系列的對(duì)象交互。中介者使各對(duì)象不需要顯式地相互引用，從而使其耦合松散，而且可以獨(dú)立地改變它們之間的交互。nvA28資訊網(wǎng)——每日最新資訊28at.com

在新的分類方式中，中介模式模式被劃分至類之間的交互類別中，其簡(jiǎn)化的是一組類之間復(fù)雜的交互關(guān)系。nvA28資訊網(wǎng)——每日最新資訊28at.com

nvA28資訊網(wǎng)——每日最新資訊28at.com

模式應(yīng)用前案例

現(xiàn)實(shí)生活中房屋中介用于連接眾多買賣的雙方，其實(shí)就是中介模式在現(xiàn)實(shí)中的應(yīng)用，下面我們就拿這個(gè)案例來進(jìn)行說明。先來看一下未使用中介模式前的代碼實(shí)現(xiàn)。nvA28資訊網(wǎng)——每日最新資訊28at.com

public class Buyer {//買家private final String name;public Buyer(String name) {this.name = name;    }public void sendMessage(Seller seller, String message) {        System.out.println(this.name + " sends a message: " + message+ " to " + seller.getName());    }public String getName() {return this.name;    }}public class Seller {//賣家private final String name;public Seller(String name) {this.name = name;    }public void sendMessage(Buyer buyer, String message) {        System.out.println(this.name + " sends a message: " + message + " to " + buyer.getName());    }public String getName() {return this.name;    }}public class Client {//調(diào)用者代碼public static void main(String[] args) {// 創(chuàng)建兩個(gè)賣家對(duì)象        Seller seller1 = new Seller("Seller A");        Seller seller2 = new Seller("Seller B");//創(chuàng)建兩個(gè)買家對(duì)象        Buyer buyer1 = new Buyer("Buyer A");        Buyer buyer2 = new Buyer("Buyer B");// 直接讓賣家之間進(jìn)行通信        seller1.sendMessage(buyer1, "Hello, are you interested in collaborating?");        seller2.sendMessage(buyer2, "Yes, I am open to collaboration opportunities.");// 其他邏輯...    }}

從上述代碼來看，最主要的問題就是買家類和賣家類直接發(fā)生耦合，后續(xù)維護(hù)非常困難。nvA28資訊網(wǎng)——每日最新資訊28at.com

結(jié)構(gòu)

nvA28資訊網(wǎng)——每日最新資訊28at.com

中介模式的示例代碼實(shí)現(xiàn)如下。nvA28資訊網(wǎng)——每日最新資訊28at.com

public abstract class Colleague {protected  Mediator mediator;public Colleague(Mediator mediator){this.mediator = mediator;    }public abstract void send(String message);public abstract void receive(String message);}public class ConcreteColleague1 extends Colleague{public ConcreteColleague1(Mediator mediator) {super(mediator);    }@Overridepublic void send(String message) {        System.out.println("Colleague 1 sends: " + message);        mediator.send(message, this);    }@Overridepublic void receive(String message) {        System.out.println("Colleague 1 receives: " + message);    }}public class ConcreteColleague2 extends Colleague{public ConcreteColleague2(Mediator mediator) {super(mediator);    }@Overridepublic void send(String message) {        System.out.println("Colleague 2 sends: " + message);        mediator.send(message, this);    }@Overridepublic void receive(String message) {        System.out.println("Colleague 2 receives: " + message);    }}public abstract class Mediator {public abstract void send(String message, Colleague colleague);}public class ConcreteMediator extends Mediator{private ConcreteColleague1 colleague1;private ConcreteColleague2 colleague2;public void setColleague1(Colleague colleague1) {this.colleague1 = (ConcreteColleague1) colleague1;    }public void setColleague2(Colleague colleague2) {this.colleague2 = (ConcreteColleague2) colleague2;    }@Overridepublic void send(String message, Colleague colleague) {if (colleague == colleague1) {            colleague2.receive("Message from 1 to 2");        } else if (colleague == colleague2) {            colleague1.receive("Message from 2 to 1");        }    }}public class Client {public static void main(String[] args) {        ConcreteMediator mediator = new ConcreteMediator();        Colleague colleague1 = new ConcreteColleague1(mediator);        Colleague colleague2 = new ConcreteColleague2(mediator);        mediator.setColleague1(colleague1);        mediator.setColleague2(colleague2);        colleague1.send("Hello from A");        colleague2.send("Hello from B");    }}

從中介模式的結(jié)構(gòu)來看，原來Colleague的各個(gè)實(shí)現(xiàn)類之間需要直接交互，現(xiàn)在交互邏輯統(tǒng)一移到Mediator實(shí)現(xiàn)類中實(shí)現(xiàn)，從而Colleague各個(gè)實(shí)現(xiàn)類之間可以實(shí)現(xiàn)松耦合。nvA28資訊網(wǎng)——每日最新資訊28at.com

模式應(yīng)用后案例

上面房屋中介的案例，在使用中介模式之后的代碼實(shí)現(xiàn)如下。nvA28資訊網(wǎng)——每日最新資訊28at.com

買家和賣家的家族類如下。nvA28資訊網(wǎng)——每日最新資訊28at.com

public interface IPerson {// 買家賣家接口String getName();void sendMessage(String message);void receiveMessage(String message);}public class Buyer implements IPerson{//具體買家類private final String name;private final IEstateMediator mediator;public Buyer(IEstateMediator mediator, String name){this.mediator=mediator;this.name=name;        mediator.registerPerson(this);    }@Overridepublic String getName(){return this.name;}@Overridepublic void sendMessage(String msg){//System.out.print(this.name +" sends a message: "+msg+"/n");this.mediator.sendMessage(msg,this);    }@Overridepublic void receiveMessage(String msg){        System.out.print(this.name +" receives a messages:"+msg+"/n");    }}public class Seller implements IPerson {// 具體賣家類private final String name;private final IEstateMediator mediator;public Seller(IEstateMediator mediator, String name){this.mediator=mediator;this.name=name;        mediator.registerPerson(this);    }@Overridepublic String getName(){return this.name;}@Overridepublic void sendMessage(String msg){//System.out.print(this.name +" sends a message: "+msg+"/n");this.mediator.sendMessage(msg,this);    }@Overridepublic void receiveMessage(String msg){        System.out.print(this.name +" receives a messages:"+msg+"/n");    }}

房屋中介的家族類如下。nvA28資訊網(wǎng)——每日最新資訊28at.com

public interface IEstateMediator {//中介者接口void registerPerson(IPerson person);void sendMessage(String message, IPerson person);}public class RealEstateMediator implements IEstateMediator {public List<IPerson> getSellers() {return this.sellers;    }public List<IPerson> getBuyers() {return this.buyers;    }private final List<IPerson> sellers = new ArrayList<>();private final List<IPerson> buyers = new ArrayList<>();@Overridepublic void registerPerson(IPerson person) {if(person instanceof Seller) {this.sellers.add(person);        }else if(person instanceof Buyer) {this.buyers.add(person);        }    }@Overridepublic void sendMessage(String message, IPerson person) {// 具體中介者類if(person instanceof Seller) {//說明是賣家發(fā)給買家for(IPerson buyer : this.buyers) {// 處理從賣家發(fā)出的消息，并轉(zhuǎn)發(fā)給其他買家                System.out.println(person.getName() + " sends message: " + message +" to " + buyer.getName());                buyer.receiveMessage(message);            }        }else if(person instanceof  Buyer) {//說明是買家發(fā)給賣家for(IPerson seller : this.sellers) {// 處理從買家發(fā)出的消息，并轉(zhuǎn)發(fā)給其他賣家                System.out.println(person.getName() + " sends message: " + message +" to " + seller.getName());                seller.receiveMessage(message);            }        }    }}

最后，調(diào)用方代碼實(shí)現(xiàn)如下。nvA28資訊網(wǎng)——每日最新資訊28at.com

public class Client {//調(diào)用方代碼public static void main(String[] args) {// 創(chuàng)建房地產(chǎn)中介對(duì)象        IEstateMediator mediator = new RealEstateMediator();// 創(chuàng)建兩個(gè)賣家對(duì)象，并注冊(cè)到房地產(chǎn)中介        IPerson seller1 = new Seller(mediator, "Seller A");        IPerson seller2 = new Seller(mediator, "Seller B");// 創(chuàng)建兩個(gè)買家對(duì)象，并注冊(cè)到房地產(chǎn)中介        IPerson buyer1 = new Buyer(mediator, "Buyer A");        IPerson buyer2 = new Buyer(mediator, "Buyer B");// 賣家發(fā)送消息給其他買家        seller1.sendMessage("Hello, I am a seller, are you interested in collaborating?");        seller2.sendMessage("Yes, I am a seller, I am open to collaboration opportunities.");// 買家發(fā)送消息給其他賣家        buyer1.sendMessage("Hello, I am a buyer, are you interested in collaborating?");        buyer2.sendMessage("Yes, I am a buyer, I am open to collaboration opportunities.");// 其他邏輯...    }}

從最終的調(diào)用方代碼來看，買家和賣家在發(fā)送消息時(shí)，都不需要再關(guān)注具體的賣家或買家，兩者之間實(shí)現(xiàn)松耦合。買家和賣家之間關(guān)系的邏輯都放在房屋中介類中實(shí)現(xiàn)。nvA28資訊網(wǎng)——每日最新資訊28at.com

適用場(chǎng)景

中介者模式適用于以下場(chǎng)景：nvA28資訊網(wǎng)——每日最新資訊28at.com

1)一組對(duì)象以定義良好但是復(fù)雜的方式進(jìn)行通信。產(chǎn)生的相互依賴關(guān)系結(jié)構(gòu)混亂且難以理解nvA28資訊網(wǎng)——每日最新資訊28at.com

2)一個(gè)對(duì)象引用其它很多對(duì)象并且直接與這些對(duì)象通信，導(dǎo)致難以復(fù)用該對(duì)象。nvA28資訊網(wǎng)——每日最新資訊28at.com

3)需要通過一個(gè)中心化的調(diào)度器來協(xié)調(diào)多個(gè)對(duì)象之間的交互，并減少對(duì)象直接通信帶來的復(fù)雜性時(shí)nvA28資訊網(wǎng)——每日最新資訊28at.com

4)希望能夠降低系統(tǒng)內(nèi)各個(gè)組件之間依賴關(guān)系、提高系統(tǒng)靈活性和可維護(hù)性時(shí)，可以使用中介者模式nvA28資訊網(wǎng)——每日最新資訊28at.com

5)一些具有交互邏輯但不應(yīng)該彼此直接知道對(duì)方存在的類nvA28資訊網(wǎng)——每日最新資訊28at.com

模式可能存在的困惑

困惑1：在中介者結(jié)構(gòu)中，中介Mediator家族類被定性為核心類。我們知道Mediator及實(shí)現(xiàn)類中只是負(fù)責(zé)管理關(guān)系，似乎核心業(yè)務(wù)邏輯還是在Colleage實(shí)現(xiàn)類中，如何解釋？nvA28資訊網(wǎng)——每日最新資訊28at.com

現(xiàn)實(shí)世界中很多場(chǎng)景下，實(shí)際上關(guān)系本身可能要比產(chǎn)生關(guān)系的具體系統(tǒng)要更有價(jià)值。比如，對(duì)于房屋中介，能盡快促成交易的前提是必須維護(hù)很多買家和賣家，并通過大數(shù)據(jù)分析，找到可能潛在會(huì)發(fā)生交易的買家和賣家之間的關(guān)系，這種關(guān)系的發(fā)現(xiàn)本身是很有價(jià)值的。因此，中介家族類歸屬于核心類別中。nvA28資訊網(wǎng)——每日最新資訊28at.com

本質(zhì)

在面向?qū)ο蟮暮芏鄨?chǎng)景應(yīng)用中，我們會(huì)盡量簡(jiǎn)化眾多交互者之間的關(guān)系，比如通過減少交互數(shù)量或者將交互確定性等手段。nvA28資訊網(wǎng)——每日最新資訊28at.com

然而，現(xiàn)實(shí)中也有一些場(chǎng)景，眾多交互者之間確實(shí)有交互的需求，并且這種交互具有不確定性。nvA28資訊網(wǎng)——每日最新資訊28at.com

中介者模式的本質(zhì)在于通過管理關(guān)系的復(fù)雜性獲得價(jià)值，從而使發(fā)生關(guān)系的眾多參與方解耦。nvA28資訊網(wǎng)——每日最新資訊28at.com

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