观察者模式实现之EventBus(Google) 设计模式

观察者模式又叫发布-订阅（publish/subscribe）模式，定义了一种一对多的依赖关系，让多个观察者对象同时监听某一个主题对象。这个主题对象在状态上发生变化时，会通知所有观察者对象，使他们能够自动更新自己，我们第一时间可能会想到消息队列，但如果在同一个JVM进程中要实现这种观察者模式该怎么去做？我们可能会想到JDK内置的java.util.Observer，或者自己写代码，其实Google提供的guava工具包也有类似的实现，这就是EventBus,可以在github中通过guava的wiki中找到eventbus的wiki信息，地址为https://github.com/google/guava/wiki/EventBusExplained，示例demo如下

public class EventBusFactory {private static final EventBus eventBusInstance = new EventBus(); private EventBusFactory() { }/** * 获取事件总线 * @return */ public static EventBus getInstance(){ return eventBusInstance; }/** * 注册观察者对象 * @param object */ public static void register(Object object){ eventBusInstance.register(object); }/** * 取消注册观察者对象 * @param object */ public static void unRegister(Object object){ eventBusInstance.unregister(object); }/** * 投递事件 * @param object */ public static void post(Object object){ eventBusInstance.post(object); } }public class OrderEvent { private Long orderId; private Integer changeType; public OrderEvent(Long orderId, Integer changeType) { this.orderId = orderId; this.changeType = changeType; }public Long getOrderId() { return orderId; }public void setOrderId(Long orderId) { this.orderId = orderId; }public Integer getChangeType() { return changeType; }public void setChangeType(Integer changeType) { this.changeType = changeType; } }public class OrderMsgObserver {@Subscribe public void OrderSyncToMq(OrderEvent event) { Integer changeType= event.getChangeType(); Long orderId =event.getOrderId(); System.out.println("订单开始发送MQ-》订单Id:"+orderId+"&变更类型:"+changeType); String msgInfo=""; if(changeType ==1){ msgInfo="this order has been issued"; }else if(changeType ==2){ msgInfo ="this order has been finshed"; }else if(changeType ==0){ msgInfo="this order has been cancel "; } writeMq(orderId,msgInfo); }public static void writeMq(Long orderId,String msgInfo){ System.out.println("发送MQ完成-》orderId:"+orderId+"&消息内容"+msgInfo); } }public class OrderSyncDbObserver {@Subscribe public void OrderSyncToDb(OrderEvent event) { Integer changeType= event.getChangeType(); Long orderId =event.getOrderId(); System.out.println("订单开始写库-》订单Id:"+orderId+"&变更类型:"+changeType); String orderInfo=""; if(changeType ==1){ orderInfo="The order has been issued"; }else if(changeType ==2){ orderInfo ="The order has been finshed"; }else if(changeType ==0){ orderInfo="The order has been cancel "; } writeDb(orderId,orderInfo); }public static void writeDb(Long orderId,String orderInfo){ System.out.println("写库完成-》orderId:"+orderId+"&变更内容"+orderInfo); } } @Test public void testEventBus(){ OrderSyncDbObserver orderSyncDbObserver =new OrderSyncDbObserver(); OrderMsgObserver orderMsgObserver =new OrderMsgObserver(); System.out.println("注册写库观察者"); EventBusFactory.getInstance().register(orderSyncDbObserver); System.out.println("注册发消息观察者"); EventBusFactory.getInstance().register(orderMsgObserver); Long orderId=1298932323L; System.out.println("开始投递事件-》订单Id:"+orderId); EventBusFactory.getInstance().post(new OrderEvent(orderId,1)); System.out.println("投递事件完成-》订单Id:"+orderId); }

测试结果如下：

注册写库观察者注册发消息观察者开始投递事件-》订单Id:1298932323 订单开始写库-》订单Id:1298932323&变更类型:1 写库完成-》orderId:1298932323&变更内容The order has been issued 订单开始发送MQ-》订单Id:1298932323&变更类型:1 发送MQ完成-》orderId:1298932323&消息内容this order has been issued 投递事件完成-》订单Id:1298932323

【观察者模式实现之EventBus(Google)】