在商城系统中使用设计模式----策略模式之在spring中使用观察者模式和发布/订阅

package java.util;

public interface Observer {
    /**
　　　*　每当观察对象发生变化时，都会调用此方法。
     *
     * @param   o     the observable object.
     * @param   arg   an argument passed to the <code>notifyObservers</code>
     *                 method.
     */
    void update(Observable o, Object arg);
}

package java.util;


public class Observable {
    private boolean changed = false;
    private Vector<Observer> obs;

    /** Construct an Observable with zero Observers. */
    public Observable() {
        obs = new Vector<>();
    }

    /**
     *　　添加观察者
     * @param   o   an observer to be added.
     * @throws NullPointerException   if the parameter o is null.
     */
    public synchronized void addObserver(Observer o) {
        if (o == null)
            throw new NullPointerException();
        if (!obs.contains(o)) {
            obs.addElement(o);
        }
    }

    /**
     * 删除观察者
     * @param   o   the observer to be deleted.
     */
    public synchronized void deleteObserver(Observer o) {
        obs.removeElement(o);
    }

    /**　　　　
　　　* 方法被调用的时候
     * 通知观察者
     *
     * @see     java.util.Observable#clearChanged()
     * @see     java.util.Observable#hasChanged()
     * @see     java.util.Observer#update(java.util.Observable, java.lang.Object)
     */
    public void notifyObservers() {
        notifyObservers(null);
    }

    /**
     * 通知观察者*/
    public void notifyObservers(Object arg) {
        /*
         * a temporary array buffer, used as a snapshot of the state of
         * current Observers.
         */
        Object[] arrLocal;

        synchronized (this) {
            /* 
　　　　　　　 * 同步保证在通知的时候，此资源不被其他所占用，避免发生在这个时候观察者发生变化
　　　　　　　 *
             */
            if (!changed)
                return;
            arrLocal = obs.toArray();
            clearChanged();
        }

        for (int i = arrLocal.length-1; i>=0; i--)
            ((Observer)arrLocal[i]).update(this, arg);
    }

    /**
     * Clears the observer list so that this object no longer has any observers.
     */
    public synchronized void deleteObservers() {
        obs.removeAllElements();
    }

    /**
     * Marks this <tt>Observable</tt> object as having been changed; the
     * <tt>hasChanged</tt> method will now return <tt>true</tt>.
     */
    protected synchronized void setChanged() {
        changed = true;
    }

    /**
     * Indicates that this object has no longer changed, or that it has
     * already notified all of its observers of its most recent change,
     * so that the <tt>hasChanged</tt> method will now return <tt>false</tt>.
     * This method is called automatically by the
     * <code>notifyObservers</code> methods.
     *
     * @see     java.util.Observable#notifyObservers()
     * @see     java.util.Observable#notifyObservers(java.lang.Object)
     */
    protected synchronized void clearChanged() {
        changed = false;
    }

    /**
     * Tests if this object has changed.
     *
     * @return  <code>true</code> if and only if the <code>setChanged</code>
     *          method has been called more recently than the
     *          <code>clearChanged</code> method on this object;
     *          <code>false</code> otherwise.
     * @see     java.util.Observable#clearChanged()
     * @see     java.util.Observable#setChanged()
     */
    public synchronized boolean hasChanged() {
        return changed;
    }

    /**
     * Returns the number of observers of this <tt>Observable</tt> object.
     *
     * @return  the number of observers of this object.
     */
    public synchronized int countObservers() {
        return obs.size();
    }
}

import java.util.Observable;

/**
 * @description:被观察者
 * @author: Chen
 * @create: 2019-04-03 23:01
 **/
public class PayObservable extends Observable {



    @Override
    public void notifyObservers() {
        System.out.println("有人下单啦");
        setChanged();
        super.notifyObservers();
    }
}

/**
 * @description:佣金观察者
 * @author: Chen
 * @create: 2019-04-03 22:55
 **/
public class CommissionObserver implements Observer {

    public CommissionObserver(Observable observable){
        observable.addObserver(this);
    }

    @Override
    public void update(Observable o, Object arg) {
        System.out.println("大家注意了，有傻逼下单了，我要开始分佣金了");
    }
}

package com.chen.observer;

import java.util.Observable;
import java.util.Observer;

/**
 * @description:消息观察者
 * @author: Chen
 * @create: 2019-04-03 22:50
 **/
public class MsgObserver implements Observer {

    public MsgObserver(Observable observable){
        observable.addObserver(this);
    }

    @Override
    public void update(Observable o, Object arg) {
        System.out.println("管理员，有人下单啦。");
    }
}

package com.chen.observer;

import java.util.Observable;
import java.util.Observer;

/**
 * @description:订单观察者
 * @author: Chen
 * @create: 2019-04-03 22:49
 **/
public class OrderObserver implements Observer {

    public OrderObserver(Observable observable){
        observable.addObserver(this);
    }

    @Override
    public void update(Observable o, Object arg) {
        System.out.println("赶紧把订单改成已支付");
    }
}

/**
 * @description:当用户下单成功后，要执行 修改订单状态，分佣，通知店主发货
 * @author: Chen
 * @create: 2019-04-03 22:34
 **/
public class ObserverMain {

    public static void main(String[] args) {

        PayObservable payObservable = new PayObservable();

        new CommissionObserver(payObservable);
        new MsgObserver(payObservable);
        new OrderObserver(payObservable);

        payObservable.notifyObservers();
    }
}