Java中的事件通知

Question

在java中，我对观察者模式或JMS感到非常困惑。我希望像下面这样使用事件通知。让我们忘记那些JMS或观察者，您认为这是可能的还是可行的？如果是，如何完成？

newSalesOrder = new SalesOrder();
newSalesOrder.notified("new SalesOrder order ID="+orderId);

EventRegister.bindEvent(SalesOrder.class, Delivery.class);
EventRegister.bindEvent(SalesOrder.class, Warehouse.class);

////////////
Delivery delivery = new Delivery();
delivery.listerning(new Event(source){
  if(source == SalesOrder.class){

  }  
});

//////////
Warehouse warehouse = new Warehouse();
warehouse.listerning(new Event(source){
  if(source == SalesOrder.class){

  }  
});

///////////
EventRegister{
    static bindEvent(Class source, Class destination){
      //???
    }
}

Answer 1

您需要注册(绑定)对象，而不是类。您可以在EventRegister中保持注册列表的静态，但我认为最好将它们作为SalesOrder的实例。所以应该是：

import java.util.ArrayList;
import java.util.List;

public class Test {
    public static void main(String[] args) {
        SalesOrder mySalesOrder = new SalesOrder();

        Warehouse myWarehouse = new Warehouse();
        mySalesOrder.addListener(myWarehouse);

        Delivery myDelivery = new Delivery();
        mySalesOrder.addListener(myDelivery);

        Event myEvent = new Event();
        // Now 'myDelivery' and 'myWarehouse' objects will receive 'myEvent'
        // object on their 'onEvent(Event event)' method
        System.out.println("Event to be published: " + myEvent);
        mySalesOrder.publishEvent(myEvent);
    }
}

interface Listener {
    public void onEvent(Event event);
}

class Event {
    // Add reqired detail here!
}

class SalesOrder {
    private List<Listener> listeners = new ArrayList<Listener>();

    public void addListener(Listener listener) {
        listeners.add(listener);
    }

    public void removeListener(Listener listener) {
        listeners.remove(listener);
    }

    // Use proper access modifier
    public void publishEvent(Event event) {
        System.out.println(this + " is goint to publish " + event
                + " to " + listeners + " listeners.");
        for (Listener listener : listeners) {
            listener.onEvent(event);
        }
    }

    // ...
}

class Warehouse implements Listener {
    public void onEvent(Event event) {
        // Do something when event received
        System.out.println(event + " received at " + this);
    }
    // ...
}

class Delivery implements Listener {
    public void onEvent(Event event) {
        // Do something when event received
        System.out.println(event + " received at " + this);
    }
    // ...
}

如果您运行它，它将打印如下内容：

即将发布的

事件: Event@190d11

SalesOrder@a 90653将发布事件@190d11到Warehouse@de6ched，传递@c 17164侦听器。

事件@190d 11在仓库收到

事件@190d 11送货处收到@c 17164

这是一个简单的示例，在现实生活中，您可以考虑使用线程安全的实现，并使用组合或继承从SalesOrder中重构注册。