中介者模式

中介者模式定义：用一个中介对象封装一系列对象交互，中介者使各对象不需要显示地相互作用，从而使其耦合松散，而且可以独立地改变他们之间的交互（Define an object that encapsulates how a set of objects interact. Mediator promotes loose coupling by keeping objects from referring to each other explicitly, and it lets you vary their interaction independently）。

中介者模式的通用类图如下：

Mediator抽象中介者角色，抽象中介者角色定义统一的接口，用于各同事角色之间通信。
ConcreteMediator具体中介者角色，通过协调同事角色实现协作行为，因此必须依赖各个同事角色
Colleague抽象同事类，指定中介者
ConcreteColleague具体同事类，每个同事都知道中介者角色，而且在与其他的同事进行通信时，一定通过中介者角色的协调。每个同事类的角色分为两种，一种是处理同时本身的行为，比如改变对象本身的状态；一种是必须依赖中介者才能完成的行为，叫做依赖方法。

public abstract class Mediator {

//具体的同事类
protected ConcreteColleague1 colleague1;
protected ConcreteColleague2 colleague2;
public void setColleague1(ConcreteColleague1 colleague1){
    this.colleague1 = colleague1;
}
public void setColleague2(ConcreteColleague2 colleague2){
    this.colleague2 = colleague2;
}
//中介者模式的业务逻辑
public abstract void doSomething1();
public abstract void doSomething2();

}

public class ConcreteMediator extends Mediator{

@Override
public void doSomething1() {
    // TODO Auto-generated method stub
    super.colleague2.selfMethod();
}
@Override
public void doSomething2() {
    // TODO Auto-generated method stub
    super.colleague1.selfMethod();
}

}

public abstract class Colleague {

protected Mediator mediator;
public Colleague(Mediator mediator){
    this.mediator = mediator;
}

}

public class ConcreteColleague1 extends Colleague{

public ConcreteColleague1(Mediator mediator) {
    super(mediator);
    mediator.setColleague1(this);
    // TODO Auto-generated constructor stub
}
public void selfMethod(){
    //该类自己的业务逻辑
    System.out.println("This is a self-method");
}
public void depMethod(){
    //该类与其它类有关联的业务逻辑
    super.mediator.doSomething1();
}

}

public class ConcreteColleague2 extends Colleague{

public ConcreteColleague2(Mediator mediator) {
    super(mediator);
    mediator.setColleague2(this);
    // TODO Auto-generated constructor stub
}
public void selfMethod(){
    System.out.println("This is a self method in colleague2");
}
public void depMethod(){
    System.out.println("This is a dependent method in colleague2");
    super.mediator.doSomething2();
}

}

public class Client {

/**
 * @param args
 */
public static void main(String[] args) {
    // TODO Auto-generated method stub
    Mediator mediator = new ConcreteMediator();
    ConcreteColleague1 colleague1 = new ConcreteColleague1(mediator);
    ConcreteColleague2 colleague2 = new ConcreteColleague2(mediator);
    colleague1.depMethod();
    colleague2.depMethod();
}

}

中介者模式的优点

中介者模式的优点是减少类间依赖，将原有的一对多的关系转化为一对一的依赖关系，同事类只依赖中介者，降低了类间的耦合。

中介者模式的缺点

中介者模式的缺点是中介者会随着业务逻辑的增加而迅速膨胀，而且逻辑复杂，原本N个对象直接的相互依赖关系转化为中介者和同事类的依赖关系，同事类越多，中介者的逻辑越复杂。