Java設計模式 - 中介者模式

1.定義

用一箇中介對象來封裝一系列的對象交互，該中介者使各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。

2. 角色

• Mediator：抽象中介者
• ConcreteMediator：具體中介者
• Colleague：抽象同事類
• ConcreteColleague：具體同事類

3. 特點

• 優點：可以減少對象之間的交互，使對象解耦，將控制邏輯集中，可以簡化系統的維護。
• 缺點：因爲中介者包含了具體同事之間的交互，若設計不當，可能導致具體中介者類十分複雜。

4. 示例

Mediator：

public abstract class Mediator {

    public Map<String, Colleague> map;

    public Mediator(){
        map = new HashMap<>();
    }

    public void register(String user, Colleague colleague) {
        map.put(user, colleague);
    }

    public abstract void operation(String receiver, String msg);
}

ConcreteMediator：

public class ConcreteMediator extends Mediator {

    @Override
    public void operation(String receiver, String msg) {
        Colleague colleague = map.get(receiver);
        if (colleague != null) {
            colleague.receiveMsg(msg);
        } else {
            System.out.println(receiver + " is not exist");
        }
    }
}

Colleague：

public abstract class Colleague {

    public Mediator mediator;

    public void setMediator(Mediator mediator) {
        this.mediator = mediator;
    }

    public abstract void receiveMsg(String msg);

    public abstract void sendMsg(String receiver, String msg);
}

具體同事類：

// ConcreteColleagueA
public class ConcreteColleagueA extends Colleague {
    @Override
    public void receiveMsg(String msg) {
        System.out.println("Colleague A receives a message");
        System.out.println(msg);
    }

    @Override
    public void sendMsg(String receiver, String msg) {
        System.out.println("Colleague A sends a message");
        mediator.operation(receiver, msg);
    }
}


// ConcreteColleagueB
public class ConcreteColleagueB extends Colleague {

    @Override
    public void receiveMsg(String msg) {
        System.out.println("Colleague B receives a message");
        System.out.println(msg);
    }

    @Override
    public void sendMsg(String receiver, String msg) {
        System.out.println("Colleague B sends a message");
        mediator.operation(receiver, msg);
    }
}

測試類：

public class TestMediator {

    public static void main(String[] args) {

        Mediator mediator = new ConcreteMediator();
        Colleague colleagueA = new ConcreteColleagueA();
        Colleague colleagueB = new ConcreteColleagueB();
        colleagueA.setMediator(mediator);
        colleagueB.setMediator(mediator);
        mediator.register("A", colleagueA);
        mediator.register("B", colleagueB);

        colleagueA.sendMsg("B","the message is from colleague A");
        System.out.println("--------------------------------------------------");
        colleagueB.sendMsg("A", "the message is from colleague B");
        System.out.println("--------------------------------------------------");
        colleagueA.sendMsg("C", "the message is from colleague A");
    }
}


// 輸出
// Colleague A sends a message
// Colleague B receives a message
// the message is from colleague A
// --------------------------------------------------
// Colleague B sends a message
// Colleague A receives a message
// the message is from colleague B
// --------------------------------------------------
// Colleague A sends a message
// C is not exist

 

參考：

1. 《Head First 設計模式》

2. 《圖說設計模式》https://design-patterns.readthedocs.io/zh_CN/latest/behavioral_patterns/mediator.html