Nacos源码之客户端实例注册分析

客户端服务注册入口

流程图：

实际上我们在真实的生产环境中，我们要让某一个服务注册到Nacos中，我们首先要引入一个：

<dependency>
 <groupId>com.alibaba.cloud</groupId>
 <artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId>
</dependency>

在引入这个依赖以后，我们要找到SpringBoot自动装配文件META-INF/spring.factories文件：

然后再通过SpingBoot的自动装配（首先找到）来加载EnableAutoConfiguration对应的类，然后这里我们就能看见很多Nacos相关的内容，那我们怎么能知道这个服务在注册的时候具体走的时候哪一个，其实一般这种文件我们都会找“Auto”关键子的文件来进行查看，然后我们现在要了解的是客户端的注册，所以我们要找“NacosServiceRegistryAutoConfiguration”。

然后在当前这个类中会有很多的Bean组件，这些都是Spring容器启动时候自动注入的，一般情况下可能我们会看一下每一个Bean组件初始化具体干了什么，但是实际上这里最核心的是“NacosAutoServiceRegistration”

/**
 * @author xiaojing
 * @author <a href="mailto:mercyblitz@gmail.com">Mercy</a>
 */
@Configuration(proxyBeanMethods = false)
@EnableConfigurationProperties
@ConditionalOnNacosDiscoveryEnabled
@ConditionalOnProperty(value = "spring.cloud.service-registry.auto-registration.enabled",
      matchIfMissing = true)
@AutoConfigureAfter({ AutoServiceRegistrationConfiguration.class,
      AutoServiceRegistrationAutoConfiguration.class,
      NacosDiscoveryAutoConfiguration.class })
public class NacosServiceRegistryAutoConfiguration {

   @Bean
   public NacosServiceRegistry nacosServiceRegistry(
         NacosDiscoveryProperties nacosDiscoveryProperties) {
      return new NacosServiceRegistry(nacosDiscoveryProperties);
   }

   @Bean
   @ConditionalOnBean(AutoServiceRegistrationProperties.class)
   public NacosRegistration nacosRegistration(
         ObjectProvider<List<NacosRegistrationCustomizer>> registrationCustomizers,
         NacosDiscoveryProperties nacosDiscoveryProperties,
         ApplicationContext context) {
      return new NacosRegistration(registrationCustomizers.getIfAvailable(),
            nacosDiscoveryProperties, context);
   }

   @Bean
   @ConditionalOnBean(AutoServiceRegistrationProperties.class)
   public NacosAutoServiceRegistration nacosAutoServiceRegistration(
         NacosServiceRegistry registry,
         AutoServiceRegistrationProperties autoServiceRegistrationProperties,
         NacosRegistration registration) {
      return new NacosAutoServiceRegistration(registry,
            autoServiceRegistrationProperties, registration);
   }

}

NacosAutoServiceRegistration

这个类就是注册的核心，所以我们来看一下它的继承关系：

通过这里我们可以清楚的知道NacosAutoServiceRegistration继承了AbstractAutoServiceRegistration，而这个类实现了ApplicationListener接口，所以我们由此得出一般实现ApplicationListener接口的类都会实现一个方法"onApplicationEvent"，这个方法会在项目启动的时候触发

public void onApplicationEvent(WebServerInitializedEvent event) {
 bind(event);
}

@Deprecated
public void bind(WebServerInitializedEvent event) {
 ApplicationContext context = event.getApplicationContext();
 if (context instanceof ConfigurableWebServerApplicationContext) {
     if ("management".equals(((ConfigurableWebServerApplicationContext) context)
                             .getServerNamespace())) {
         return;
     }
 }
 this.port.compareAndSet(0, event.getWebServer().getPort());
 this.start();
}

然后在start()方法中调用register()方法来注册服务：

public void start() {
 if (!isEnabled()) {
     if (logger.isDebugEnabled()) {
         logger.debug("Discovery Lifecycle disabled. Not starting");
     }
     return;
 }

 // only initialize if nonSecurePort is greater than 0 and it isn't already running
 // because of containerPortInitializer below
 if (!this.running.get()) {
     this.context.publishEvent(
         new InstancePreRegisteredEvent(this, getRegistration()));
     register();
     if (shouldRegisterManagement()) {
         registerManagement();
     }
     this.context.publishEvent(
         new InstanceRegisteredEvent<>(this, getConfiguration()));
     this.running.compareAndSet(false, true);
 }

}

分析到这里我们就能知道真实的服务注册入口是通过调用register()这个方法来注册的：

protected void register() {
 //serviceRegistry实际上是一个接口，它的具体实现类NacosServiceRegistry
 this.serviceRegistry.register(getRegistration());
}

查看NacosServiceRegistry实现类中register()注册方法，这里其实调用了registerInstance注册实例方法：

@Override
public void register(Registration registration) {

 if (StringUtils.isEmpty(registration.getServiceId())) {
     log.warn("No service to register for nacos client...");
     return;
 }

 NamingService namingService = namingService();
 String serviceId = registration.getServiceId();
 String group = nacosDiscoveryProperties.getGroup();
	//构建instance实例
 Instance instance = getNacosInstanceFromRegistration(registration);

 try {
     //向服务端注册此服务
     namingService.registerInstance(serviceId, group, instance);
     log.info("nacos registry, {} {} {}:{} register finished", group, serviceId,
              instance.getIp(), instance.getPort());
 }
 catch (Exception e) {
     log.error("nacos registry, {} register failed...{},", serviceId,
               registration.toString(), e);
     // rethrow a RuntimeException if the registration is failed.
     // issue : https://github.com/alibaba/spring-cloud-alibaba/issues/1132
     rethrowRuntimeException(e);
 }
}