中介者模式

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中介者模式

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• 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。