定義

用一箇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引用，從而使其耦合鬆散，而且可以獨立地改變它們之間的互動。

角色

• Colleague：是一個抽象類或者介面，提供和其他Colleague通訊的方法 notify(String name)。引數name是其他Colleague的名字。
• ColleagueA，ColleagueB： 都是Colleague的實現類。
• Mediator: 中介者類，聚合了一系列的同事類，使得它們之間可以相互通訊。具體同事類ColleagueA等都是通過Mediator，呼叫Mediator的notify（String name）方法向其他同事類傳送訊息。notify(String name)通過name找到集合中對應的Colleague並向其傳遞訊息。Mediator類提供add(Colleague colleague)方法增加自己維護的Colleague集合中的物件。

UML

實現

/**
 * desc : 同事介面
 * Created by tiantian on 2018/9/23
 */
public interface Colleague {
    
    void notify(String name);
    
    void receive();
    
    String getName();
}

/**
 * desc : 具體同事A
 * Created by tiantian on 2018/9/23
 */
public class ColleagueA implements Colleague{

    private String name;

    public ColleagueA(String name) {
        this.name = name;
    }
    
    @Override
    public void notify(String name) {
        Mediator.notify(name);
    }

    @Override
    public void receive() {
        System.out.println("ColleagueA received message");
    }

    @Override
    public String getName() {
        return name;
    }
}
 

/**
 * desc : 具體同事A
 * Created by tiantian on 2018/9/23
 */
public class ColleagueB implements Colleague{
    
    private String name;

    public ColleagueB(String name) {
        this.name = name;
    }

    @Override
    public void notify(String name) {
        Mediator.notify(name);
    }

    @Override
    public void receive() {
        System.out.println("ColleagueB received message");
    }

    @Override
    public String getName() {
        return name;
    }
}
 

/**
 * desc : 媒介類
 * Created by tiantian on 2018/9/23
 */
public class Mediator {
    
    private static Map<String, Colleague> colleagues = new HashMap<>();
    
    public static void notify(String name) {
        Colleague colleague = colleagues.get(name);
        colleague.receive();
    }
    
    public static void add(Colleague colleague) {
        colleagues.put(colleague.getName(), colleague);
    }
}

public class Test {
    public static void main(String[] args) {
        Colleague colleagueA = new ColleagueA("colleagueA");
        Colleague colleagueB = new ColleagueB("colleagueB");
        Mediator.add(colleagueA);
        Mediator.add(colleagueB);
        
        colleagueA.notify("colleagueB");
    }
}

總結

中介者模式使得物件之間網狀的依賴關係變成星型依賴關係。物件之間通訊時不必顯式的相互呼叫，而是通過中介者間接的傳遞訊息。這種依賴關係也符合迪米特原則。該模式缺點是，當需要互相通訊的同事類數量很多的時候，中介者的複雜度將變的很高，維護難度也隨之增加。