观察者模式

GoF设计模式里面的观察者模式的UML图

PS：发布和订阅（事件监听，mq，多路IO复用）
例如：XX楼盘5-1开盘，你肯定不知道，如果你想知道，肯定要去楼盘登记，留下电话号5-1号销售就会打电话通知你。

Subject 就是抽象主题：它负责管理所有观察者的引用，同时定义主要的事件操作。
ConcreteSubject 具体主题：它实现了抽象主题的所有定义的接口，当自己发生变化时，会通知所有观察者。
Observer 观察者：监听主题发生变化相应的操作接口。

代码案例

public class EventObject implements Serializable {

    private String type;
    private Object data;

    public EventObject(String type, Object data) {
        this.type = type;
        this.data = data;
    }

    public String getType() {
        return type;
    }

    public Object getData() {
        return data;
    }
}

//subject
public interface Lifecycle {

    public void addLifecycleListener(LifecycleListener listener);

    public void removeLifecycleListener(LifecycleListener listener);

    public void fireLifecycleEvent(String type,Object data);
}

//ConcreteSubject 
public class LifecycleSubject implements Lifecycle {

    private CopyOnWriteArrayList<LifecycleListener> cwal = new CopyOnWriteArrayList();

    @Override
    public void addLifecycleListener(LifecycleListener listener) {
        cwal.add(listener);
    }

    @Override
    public void removeLifecycleListener(LifecycleListener listener) {
        cwal.remove(listener);
    }

    @Override
    public void fireLifecycleEvent(String type, Object data) {

        EventObject event = new EventObject(type, data);
        for (int i = 0; i < cwal.size(); i++) {
            cwal.get(i).lifecycleEvent(event);
        }

    }
}

//观察者行为
public interface LifecycleListener {
    public void lifecycleEvent(EventObject event);
}

//具体的观察者
public class ObserverSubject implements LifecycleListener {

    @Override
    public void lifecycleEvent(EventObject event) {
        System.out.println(event.getType() + "=" + event.getData());
    }
}

public class Client {
    public static void main(String[] args) {
        LifecycleSubject lifecycleSubject = new LifecycleSubject();
        lifecycleSubject.addLifecycleListener(new ObserverSubject());
        lifecycleSubject.fireLifecycleEvent("start", "how are you");
    }
}