Guava EventBus集成spring

EventBus 不是通用的消息系统，也不是用来做进程间的通信的，而是在进程内，用于解耦两段直接调用的业务逻辑；

1、代码结构

• event：eventbus中流转的事件（消息），包结构按照业务模块在细分(比如应用部署模块就是deployment)；
• subscriber：消费者，和event 是一一对应的，一个event 对应一个消费者，包结构按照业务模块在细分(比如应用部署模块就是deployment)；
• poster：生产者，这边把生产者单独出来是为了收敛入口，这样可以方便的知道有哪些地方在生产消息，按照业务模块分为不同的类(因为生产消息的功能比较单薄)；

2、代码实现

在applicationContext.xml 中定义好EventBus

asyncEventBus

< bean  id = "taskExecutor"  class = "org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor"  lazy-init = "true" >

     < property  name = "corePoolSize"  value = "10" />

     < property  name = "maxPoolSize"  value = "50" />

     < property  name = "queueCapacity"  value = "10000" />

     < property  name = "keepAliveSeconds"  value = "300" />

     < property  name = "rejectedExecutionHandler" >

         < bean  class = "java.util.concurrent.ThreadPoolExecutor$CallerRunsPolicy" />

     </ property >

</ bean >

< bean  id = "asyncEventBus"  class = "com.google.common.eventbus.AsyncEventBus" >

     < constructor-arg  name = "executor"  ref = "taskExecutor" />

</ bean >

2.1、标准化subscriber

所有的subscriber都要实现 BaseSubscriber这个 interface

BaseSubscriber

public  interface  BaseSubscriber<E> {

 

     /**

      * event 处理逻辑入口

      **/

     void  subscribe(E event);

}

所有的subscriber在类上加上EventBusRegister 这个annotation

EventBusRegister

@Target ({ElementType.TYPE})

@Retention (RetentionPolicy.RUNTIME)

@Documented

public  @interface  EventBusRegister {

}

实现EventBusAdapter用于自动注册subscriber

EventBusAdapter

@Component

public  class  EventBusAdapter  implements  ApplicationContextAware, InitializingBean {

     @Autowired

     private  AsyncEventBus asyncEventBus;

 

     private  ApplicationContext applicationContext;

 

     @Override

     public  void  afterPropertiesSet()  throws  Exception {

         this .applicationContext.getBeansWithAnnotation(EventBusRegister. class ).forEach((name, bean) -> {

             asyncEventBus.register(bean);

         });

     }

 

     @Override

     public  void  setApplicationContext(ApplicationContext applicationContext)  throws  BeansException {

         this .applicationContext = applicationContext;

     }

}

举个例子

BuildUpdateSubscriber

@Component

@EventBusRegister

public  class  BuildUpdateSubscriber  implements  BaseSubscriber<BuildUpdateEvent> {

     @Autowired

     private  BuildService buildService;

 

     @Subscribe

     @Override

     public  void  subscribe(BuildUpdateEvent event) {

         switch  (event.getEventType()) {

             case  BUILD_CONNECTED:

                 List<BuildVo> buildVos = (List<BuildVo>) event.getData();

                 buildService.addBuildVosAndTriggerConnectEvent(buildVos);

                 break ;

             case  BUILD_ADD:

                 BuildVo addedBuildVo = (BuildVo) event.getData();

                 buildService.addBuildVoAndTriggerClientEvent(addedBuildVo);

                 break ;

             case  BUILD_MODIFY:

                 BuildVo modifiedBuildVo = (BuildVo) event.getData();

                 buildService.modifyBuildVoAndTriggerEvent(modifiedBuildVo);

                 break ;

             case  BUILD_DELETE:

                 BuildVo deletedBuildVo = (BuildVo) event.getData();

                 buildService.deleteBuildVoAndTriggerClientEvent(deletedBuildVo);

                 break ;

             default :

                 // ignore

                 break ;

         }

     }

}

3、代码实现改进

前面通过规范代码的包结构、加了一些trick使得我们可以方便的使用eventbus解耦我们的业务逻辑，但是有时候我们需要的bean被注册 的前后做一些业务逻辑，所以我们在bean 被注册到eventbus前后加了两个hook：AfterRegisterProcessor、BeforeRegisterProcessor；实现这两个interface并且实现对于的方法，会在bean 被注册前后被调用

bean 注册到eventbus前的hook

BeforeRegisterProcessor

public  interface  BeforeRegisterProcessor {

     void  beforeRegister();

}

bean 注册到eventbus后的hook

AfterRegisterProcessor

public  interface  AfterRegisterProcessor {

     void  afterRegister();

}

实现：保证在 client.watch 之前，注册已经完成，这样watch产生的消息就能够保证被成功消费

GlueService

@Service

public  class  GlueService  implements  AfterRegisterProcessor {

     @Autowired

     private  PodListener podListener;

 

     @Autowired

     private  RouteListener routerListener;

 

     @Autowired

     private  BuildListener buildListener;

 

     @Autowired

     private  DeploymentListener deploymentListener;

 

     @Autowired

     private  OpenShiftClient openShiftClient;

 

     @Override

     public  void  afterRegister() {

         IClient client = openShiftClient.getClient();

         podWatch = client.watch(podListener, ResourceKind.POD);

         routeWatch = client.watch(routerListener, ResourceKind.ROUTE);

         buildWatch = client.watch(buildListener, ResourceKind.BUILD);

         deploymentWatch = client.watch(deploymentListener, ResourceKind.REPLICATION_CONTROLLER);

     }

}