观察者模式（发布-订阅模式）

用途：可用于拦截过滤器

消息推送接口：

public interface Subject {
    //添加订阅者
    void addObserver(Observer observer);
    //移除订阅者
    void removeObserver(Observer observer);
    //通知订阅者
    void notifyObservers(String message);
}

消息推送实现着:

​
public class ConcreteSubject implements Subject{

    //订阅者集合
    ArrayList<Observer> observers = new ArrayList<>();


    @Override
    public void addObserver(Observer observer) {
        observers.add(observer);
    }

    @Override
    public void removeObserver(Observer observer) {
        observers.remove(observer);
    }

    @Override
    public void notifyObservers(String message) {
        for (Observer observer : observers) {
            observer.update(message);
        }
    }
}

​

订阅者接口

public interface Observer {
    void update(String message);

}

订阅者1

public class ObserverOne implements Observer{
    @Override
    public void update(String message) {
        System.out.println("ObserverOne"+message);
    }
}

订阅者2

public class ObserverTwo implements Observer{
    @Override
    public void update(String message) {
        System.out.println("ObserverTwo"+message);
    }
}

测试：

public class Tes {
    public static void main(String[] args) {
        ConcreteSubject concreteSubject = new ConcreteSubject();
        concreteSubject.addObserver(new ObserverOne());
        concreteSubject.addObserver(new ObserverTwo());
        concreteSubject.notifyObservers("hello world");
    }
}