类ServiceRegistryAutoConfiguration

类ServiceRegistryAutoConfiguration 用来自动配置ServiceRegistry，构建ServiceRegistryEndpoint的bean：

@Configuration
public class ServiceRegistryAutoConfiguration {

    @ConditionalOnBean(ServiceRegistry.class)
    @ConditionalOnClass(Endpoint.class)
    protected class ServiceRegistryEndpointConfiguration {
        @Autowired(required = false)
        private Registration registration;

        // 构建 ServiceRegistryEndpoint 的bean
        @Bean
        public ServiceRegistryEndpoint serviceRegistryEndpoint(ServiceRegistry serviceRegistry) {
            // new出ServiceRegistryEndpoint实例
            ServiceRegistryEndpoint endpoint = new ServiceRegistryEndpoint(serviceRegistry);
            // 设置registration（可能为null？）
            endpoint.setRegistration(registration);
            return endpoint;
        }
    }
}