一.前言

　 近期由于公司不同平台项目之间的业务整合,需要做到相互访问! 每个平台均有自己的注册中心和服务,且注册中心相互之间并没有相互注册!
　 借助spring的事件监听,在eureka-server端监听服务注册,将所有服务的ip和port存放至redis库,然后让其他平台服务通过redis库获取ip和端口号,进而进行http调用.结构图如下:

二.事件解析

事件列表

　在 org.springframework.cloud.netflix.eureka.server.event包下会发现如下类:

• EurekaInstanceCanceledEvent: 服务下线事件
• EurekaInstanceRegisteredEvent: 服务注册事件
• EurekaInstanceRenewedEvent: 服务续约事件
• EurekaRegistryAvailableEvent: eureka注册中心启动事件
• EurekaServerStartedEvent: eureka server启动时间

源码分析

　 打开 org.springframework.cloud.netflix.eureka.server.InstanceRegistry类,会发现当eureka服务续约、注册、取消等时,spring会publish不同的事件,对应的事件类就是上面的列表.

续约事件

    @Override
    public boolean renew(final String appName, final String serverId,
            boolean isReplication) {
        log("renew " + appName + " serverId " + serverId + ", isReplication {}"
                + isReplication);
        List<Application> applications = getSortedApplications();
        for (Application input : applications) {
            if (input.getName().equals(appName)) {
                InstanceInfo instance = null;
                for (InstanceInfo info : input.getInstances()) {
                    if (info.getId().equals(serverId)) {
                        instance = info;
                        break;
                    }
                }
                // 发布续约事件
                publishEvent(new EurekaInstanceRenewedEvent(this, appName, serverId,
                        instance, isReplication));
                break;
            }
        }
        return super.renew(appName, serverId, isReplication);
    }

注册事件

    @Override
    public void register(InstanceInfo info, int leaseDuration, boolean isReplication) {
        handleRegistration(info, leaseDuration, isReplication);
        super.register(info, leaseDuration, isReplication);
    }
    
        private void handleRegistration(InstanceInfo info, int leaseDuration,
            boolean isReplication) {
        log("register " + info.getAppName() + ", vip " + info.getVIPAddress()
                + ", leaseDuration " + leaseDuration + ", isReplication "
                + isReplication);
        // 发布注册事件
        publishEvent(new EurekaInstanceRegisteredEvent(this, info, leaseDuration,
                isReplication));
    }

事件监听

　 通过上面的源码追溯,我们已经得到对应的事件类了,所以现在要做的仅仅是监听对应的事件即可,至此已经完成了我们所需要对事件监听后的业务处理!

@Component
public class EurekaStateChangeListener {

    @Value("${iptable.platform}")
    private String platform;
    
    @Autowired
    private RedisTemplate<String, String> redisTemplate;

    private static Logger logger = LoggerFactory.getLogger(EurekaStateChangeListener.class);
    private static final String COLON = ":";

    @EventListener//(condition = "#event.replication==false")
    public void listen(EurekaInstanceCanceledEvent eurekaInstanceCanceledEvent) {
        // 服务断线事件
        String appName = eurekaInstanceCanceledEvent.getAppName();
        String serverId = eurekaInstanceCanceledEvent.getServerId();
        Objects.requireNonNull(appName, "服务名不能为空!");

        SetOperations<String, String> opsForSet = redisTemplate.opsForSet();
        opsForSet.remove((platform + appName).toLowerCase(), serverId);
        logger.info(">>>>>>> 失效服务:{},已被剔除!", serverId);
    }

    @EventListener//(condition = "#event.replication==false")
    public void listen(EurekaInstanceRegisteredEvent event) {
        // 服务注册
        InstanceInfo instanceInfo = event.getInstanceInfo();
        String appName = instanceInfo.getAppName();
        Objects.requireNonNull(appName, "服务名不能为空!");

        SetOperations<String, String> opsForSet = redisTemplate.opsForSet();
        opsForSet.add((platform + appName).toLowerCase(), instanceInfo.getIPAddr() + COLON + instanceInfo.getPort());
        logger.info(">>>>>>> 服务名:{},端口号:{},已缓存至redis", appName, instanceInfo.getPort());
    }

    @EventListener//(condition = "#event.replication==false")
    public void listen(EurekaInstanceRenewedEvent event) {
        // 服务续约
        logger.info(">>>>>>>>>>>>>>>Server续约:" + event.getServerId());
    }

    @EventListener
    public void listen(EurekaRegistryAvailableEvent event) {
        // 注册中心启动
        logger.info(">>>>>>>>>>>>>>>Server注册中心:" + event);
    }

    @EventListener
    public void listen(EurekaServerStartedEvent event) {
        // Server启动
        logger.info(">>>>>>>>>>>>>>>Server启动:" + event);
    }
}

注意事项

• [ ] 版本问题:

　 当时项目组用的SpringCloud版本是Brixton.RELEASE,该版本有一个问题就是服务注册和下线并不会出发对应的事件,所以导致一直监听不到.解决的办法也很简单,只要升级版本即可,我已经升级到最新版本Finchley.RELEASE.
　 传送门, 点我
　

• [ ] 重复监听:

例如,在续约的时候,eureka会发出2条EurekaInstanceRenewedEvent事件,但是2条事件的属性却不一样!一个事件的属性replication为true,另外一个为false.如果我们只想处理replication=true的事件,如下配置即可:

    @EventListener(condition = "#event.replication==false")
    public void listen(EurekaInstanceRenewedEvent event) {
        // 服务续约
        logger.info(">>>>>>>>>>>>>>>Server续约:" + event.getServerId());
    }

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GitHub代码,点我