观察者模式实现之EventBus(Google)

     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

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