Guava EventBus初体验

在工作中，经常会遇见使用异步的方式来发送事件，或者触发另外一个动作：经常用到的框架是MQ（分布式方式通知）。如果是同一个jvm里面通知的话，就可以使用guava的EventBus事件机制。

EventBus事件机制包括三个部分：事件、事件监听器、事件源。

一、引入guava的jar以及反射的jar包

<dependency>
  <groupId>com.google.guava</groupId>
  <artifactId>guava</artifactId>
  <version>21.0</version>
</dependency>

<dependency>
  <groupId>org.reflections</groupId>
  <artifactId>reflections</artifactId>
  <version>0.9.11</version>
</dependency>

二、在config下新建一个类EventBusConfig.java

import com.google.common.eventbus.AsyncEventBus;
import com.google.common.eventbus.Subscribe;
import org.reflections.Reflections;
import org.reflections.scanners.MethodAnnotationsScanner;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.stereotype.Component;

import java.lang.reflect.Method;
import java.util.Set;
import java.util.concurrent.Executors;

@Component
public class EventBusConfig {

   @Autowired
   private ApplicationContext context;

   @Bean
   @ConditionalOnMissingBean(AsyncEventBus.class)
   AsyncEventBus createEventBus() {
       AsyncEventBus eventBus = new AsyncEventBus(Executors.newFixedThreadPool(5));
       Reflections reflections = new Reflections("com.xxx", new MethodAnnotationsScanner());
       Set<Method> methods = reflections.getMethodsAnnotatedWith(Subscribe.class);
       if (null != methods ) {
           for(Method method : methods) {
               try {
                   eventBus.register(context.getBean(method.getDeclaringClass()));
               }catch (Exception e ) {
                   //register subscribe class error
               }
           }
       }

       return eventBus;
   }
}

三、利用接口封装事件发送
1、定义接口LocalEventBus.java

public interface LocalEventBus {
    void post(Event event);
}

2、定义实现类LocalEventBusImpl.java

import com.google.common.eventbus.AsyncEventBus;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

@Service
public class LocalEventBusImpl implements LocalEventBus {

    @Autowired
    private AsyncEventBus eventBus;

    @Override
    public void post(Event event) {
        if (null != event) {
            eventBus.post(event);
        }
    }
}

3、接口Event.class

public interface Event<T> {
    T getContent();
}

四、在业务工程里使用：
需要定义事件、消息体、订阅者、发送者。

1、定义login事件

public class LoginEvent implements Event<LoginMsg> {

    private LoginMsg loginMsg;

    public LoginEvent(LoginMsg loginMsg) {
        this.loginMsg = loginMsg;
    }

    @Override
    public LoginMsg getContent() {
        return this.loginMsg;
    }
}

2、定义消息体

public class LoginMsg {
    private Long uid;
    private String mobile;
    private String ip;
    private String osVersion;
    private String deviceModel;
    private String deviceToken;
}

3、定义订阅者

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

@Component
public class LoginSubscriber {

    @Subscribe
    @AllowConcurrentEvents
    public void onLogin(LoginEvent event) throws BizException {
        LoginMsg msg = event.getContent();
        Long uid = msg.getUid();
        // 具体业务
        Thread.sleep(5000);
    }
}

4、定义发送者，把消息发送到EventBus。

@Autowired
private LocalEventBus localEventBus;

LoginMsg msg = new LoginMsg(uid, mobile, ip, osVersion, deviceModel, deviceToken); 

localEventBus.post(new LoginEvent(msg));

5、controller 测试。

@Autowired
private LocalEventBus localEventBus;

@GetMapping(value = "/sendMsg/{mobile}")
    public Result sendMsg(@PathVariable("mobile") String mobile) {
        StopWatch stopWatch = new StopWatch();
        stopWatch.start();
        LoginMsg msg = new LoginMsg(1, mobile, ip, 10, 10, 10); 
        localEventBus.post(new LoginEvent(msg));
        stopWatch.stop();
        return Result.success(stopWatch.getTime());
}

结果显示，因为咱们在LoginSubscriber中设置了Thread.sleep(5000)，所以最后打印的结果可以看出asyncEventBus是异步的。如果使用的是 eventBus.post(……)那就是同步的了。