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二十一、行为型（中介者模式）

news 2024/10/28 17:40:47

中介者模式（Mediator Pattern）

概念
中介者模式是一种行为型设计模式，通过引入一个中介者对象，来减少多个对象之间的直接交互。中介者将对象之间的交互封装在一个统一的接口中，从而降低对象之间的耦合度，增强系统的可维护性和可扩展性。

应用场景

复杂的对象交互：当系统中存在多个对象并且它们之间有复杂的相互交互时，中介者模式可以帮助简化对象之间的通信。
解耦对象：当需要减少对象之间的耦合，避免直接引用时，中介者模式提供了一种良好的解耦方案。
系统扩展：当需要对系统进行扩展时，添加新的对象或功能可以通过中介者进行，而无需修改其他对象的代码。
聊天系统：在一个聊天应用中，用户通过一个中介者（如聊天服务器）进行消息的发送和接收，从而避免了用户之间的直接交互。

注意点

中介者复杂性：如果中介者承担了过多的责任，可能导致中介者本身变得复杂，从而影响系统的可维护性。
性能问题：中介者可能会引入额外的性能开销，尤其是在处理大量消息时，需要合理设计中介者的实现。
中介者的角色：中介者模式适用于对象之间存在复杂交互的情况，而在简单交互的场景中，使用中介者可能显得多余。

核心要素

Mediator（中介者接口）：定义与各个同事对象的交互接口。
ConcreteMediator（具体中介者）：实现中介者接口，协调同事对象之间的交互。
Colleague（同事接口）：定义同事对象的接口，通过中介者进行交互。
ConcreteColleague（具体同事）：实现同事接口，具体的同事对象，使用中介者与其他同事进行交互。

Java代码完整示例

示例：简单的中介者模式实现

// 中介者接口
interface Mediator {void register(Colleague colleague);void send(String message, Colleague sender);
}// 具体中介者
class ConcreteMediator implements Mediator {private List<Colleague> colleagues = new ArrayList<>();@Overridepublic void register(Colleague colleague) {colleagues.add(colleague);}@Overridepublic void send(String message, Colleague sender) {for (Colleague colleague : colleagues) {// 不发送给发送者if (colleague != sender) {colleague.receive(message);}}}
}// 同事接口
abstract class Colleague {protected Mediator mediator;public Colleague(Mediator mediator) {this.mediator = mediator;}public abstract void receive(String message);
}// 具体同事A
class ConcreteColleagueA extends Colleague {public ConcreteColleagueA(Mediator mediator) {super(mediator);}@Overridepublic void receive(String message) {System.out.println("ConcreteColleagueA received: " + message);}public void send(String message) {System.out.println("ConcreteColleagueA sending: " + message);mediator.send(message, this);}
}// 具体同事B
class ConcreteColleagueB extends Colleague {public ConcreteColleagueB(Mediator mediator) {super(mediator);}@Overridepublic void receive(String message) {System.out.println("ConcreteColleagueB received: " + message);}public void send(String message) {System.out.println("ConcreteColleagueB sending: " + message);mediator.send(message, this);}
}// 客户端代码
public class MediatorPatternDemo {public static void main(String[] args) {ConcreteMediator mediator = new ConcreteMediator();ConcreteColleagueA colleagueA = new ConcreteColleagueA(mediator);ConcreteColleagueB colleagueB = new ConcreteColleagueB(mediator);mediator.register(colleagueA);mediator.register(colleagueB);colleagueA.send("Hello, B!");colleagueB.send("Hi, A!");}
}

输出结果：

ConcreteColleagueA sending: Hello, B!
ConcreteColleagueB received: Hello, B!
ConcreteColleagueB sending: Hi, A!
ConcreteColleagueA received: Hi, A!

各种变形用法完整示例

多个同事类型的交互

通过扩展同事对象的类型，允许更多的对象参与到中介者的交互中。

代码示例：多个同事类型

// 具体同事C
class ConcreteColleagueC extends Colleague {public ConcreteColleagueC(Mediator mediator) {super(mediator);}@Overridepublic void receive(String message) {System.out.println("ConcreteColleagueC received: " + message);}public void send(String message) {System.out.println("ConcreteColleagueC sending: " + message);mediator.send(message, this);}
}public class MultiColleagueDemo {public static void main(String[] args) {ConcreteMediator mediator = new ConcreteMediator();ConcreteColleagueA colleagueA = new ConcreteColleagueA(mediator);ConcreteColleagueB colleagueB = new ConcreteColleagueB(mediator);ConcreteColleagueC colleagueC = new ConcreteColleagueC(mediator);mediator.register(colleagueA);mediator.register(colleagueB);mediator.register(colleagueC);colleagueA.send("Hello, B and C!");colleagueC.send("Hi, A and B!");}
}

中介者与同事的复杂交互

中介者可以实现更复杂的业务逻辑，如对消息进行过滤或修改。

代码示例：复杂交互

class EnhancedMediator implements Mediator {private List<Colleague> colleagues = new ArrayList<>();@Overridepublic void register(Colleague colleague) {colleagues.add(colleague);}@Overridepublic void send(String message, Colleague sender) {// 简单的消息过滤if (!message.contains("spam")) {for (Colleague colleague : colleagues) {if (colleague != sender) {colleague.receive(message);}}} else {System.out.println("Message blocked: " + message);}}
}public class EnhancedMediatorDemo {public static void main(String[] args) {EnhancedMediator mediator = new EnhancedMediator();ConcreteColleagueA colleagueA = new ConcreteColleagueA(mediator);ConcreteColleagueB colleagueB = new ConcreteColleagueB(mediator);mediator.register(colleagueA);mediator.register(colleagueB);colleagueA.send("Hello, B!");colleagueB.send("spam message"); // 这条消息将被阻止}
}

中介者的状态管理

中介者可以维护状态信息，协调同事对象的状态。

代码示例：状态管理

class StateMediator implements Mediator {private List<Colleague> colleagues = new ArrayList<>();private String state;@Overridepublic void register(Colleague colleague) {colleagues.add(colleague);}public void setState(String state) {this.state = state;notifyColleagues();}private void notifyColleagues() {for (Colleague colleague : colleagues) {colleague.receive("State updated to: " + state);}}@Overridepublic void send(String message, Colleague sender) {// 这里可以实现其他交互逻辑}
}public class StateMediatorDemo {public static void main(String[] args) {StateMediator mediator = new StateMediator();ConcreteColleagueA colleagueA = new ConcreteColleagueA(mediator);ConcreteColleagueB colleagueB = new ConcreteColleagueB(mediator);mediator.register(colleagueA);mediator.register(colleagueB);mediator.setState("Active");}
}