探究 Eureka 在 Spring Boot 中的配置注入与统一管理机制（下）——第四节

今天我们继续探讨已经加载到Spring容器中的RibbonEurekaAutoConfiguration自动配置类是如何进行初始化的。

RibbonEurekaAutoConfiguration

@Configuration(proxyBeanMethods = false)
@EnableConfigurationProperties
@ConditionalOnRibbonAndEurekaEnabled
@AutoConfigureAfter(RibbonAutoConfiguration.class)
@RibbonClients(defaultConfiguration = EurekaRibbonClientConfiguration.class)
public class RibbonEurekaAutoConfiguration {}

RibbonEurekaAutoConfiguration自动配置类注入到Spring容器之前，会为Ribbon客户端设置默认配置，同时在RibbonAutoConfiguration类被加载之后才会被注入到Spring容器中。
我们分别来看下RibbonAutoConfiguration和EurekaRibbonClientConfiguration

RibbonAutoConfiguration

@Configuration
@Conditional({RibbonClassesConditions.class})
@RibbonClients
@AutoConfigureAfter(name = {"org.springframework.cloud.netflix.eureka.EurekaClientAutoConfiguration"}
)
@AutoConfigureBefore({LoadBalancerAutoConfiguration.class, AsyncLoadBalancerAutoConfiguration.class})
@EnableConfigurationProperties({RibbonEagerLoadProperties.class, ServerIntrospectorProperties.class})
public class RibbonAutoConfiguration {……
}

• 生效的条件：在EurekaClientAutoConfiguration类加载之后被加载,且在LoadBalancerAutoConfiguration和 AsyncLoadBalancerAutoConfiguration类加载之前加载，同时Ribbon 相关类存在时才生效。
• 日志

RibbonAutoConfiguration matched:- AllNestedConditions 4 matched 0 did not; NestedCondition on RibbonAutoConfiguration.RibbonClassesConditions.RibbonPresent @ConditionalOnClass found required class 'com.netflix.ribbon.Ribbon'; NestedCondition on RibbonAutoConfiguration.RibbonClassesConditions.AsyncRestTemplatePresent @ConditionalOnClass found required class 'org.springframework.web.client.AsyncRestTemplate'; NestedCondition on RibbonAutoConfiguration.RibbonClassesConditions.RestTemplatePresent @ConditionalOnClass found required class 'org.springframework.web.client.RestTemplate'; NestedCondition on RibbonAutoConfiguration.RibbonClassesConditions.IClientPresent @ConditionalOnClass found required class 'com.netflix.client.IClient' (RibbonAutoConfiguration.RibbonClassesConditions)RibbonAutoConfiguration#loadBalancerClient matched:- @ConditionalOnMissingBean (types: org.springframework.cloud.client.loadbalancer.LoadBalancerClient; SearchStrategy: all) did not find any beans (OnBeanCondition)RibbonAutoConfiguration#propertiesFactory matched:- @ConditionalOnMissingBean (types: org.springframework.cloud.netflix.ribbon.PropertiesFactory; SearchStrategy: all) did not find any beans (OnBeanCondition)RibbonAutoConfiguration#springClientFactory matched:- @ConditionalOnMissingBean (types: org.springframework.cloud.netflix.ribbon.SpringClientFactory; SearchStrategy: all) did not find any beans (OnBeanCondition)

小结：RibbonAutoConfiguration会被注入到Spring容器中。

EurekaRibbonClientConfiguration

该配置类是为使用 Eureka 进行服务发现的 Ribbon 客户端提供自动配置。以实现负载均衡和服务发现的功能。

该配置类初始化的时候，会创建3个bean。

1. ribbonPing(IClientConfig config)方法

    @Bean@ConditionalOnMissingBeanpublic IPing ribbonPing(IClientConfig config) {if (this.propertiesFactory.isSet(IPing.class, serviceId)) {return this.propertiesFactory.get(IPing.class, config, serviceId);}NIWSDiscoveryPing ping = new NIWSDiscoveryPing();ping.initWithNiwsConfig(config);return ping;}

创建IPing类型的 Bean，用于检查Ribbon 客户端所调用的后端服务实例的健康状态。

2. ribbonServerList(IClientConfig config, Provider<EurekaClient> eurekaClientProvider)方法

    @Bean@ConditionalOnMissingBeanpublic ServerList<?> ribbonServerList(IClientConfig config,Provider<EurekaClient> eurekaClientProvider) {if (this.propertiesFactory.isSet(ServerList.class, serviceId)) {return this.propertiesFactory.get(ServerList.class, config, serviceId);}DiscoveryEnabledNIWSServerList discoveryServerList = new DiscoveryEnabledNIWSServerList(config, eurekaClientProvider);DomainExtractingServerList serverList = new DomainExtractingServerList(discoveryServerList, config, this.approximateZoneFromHostname);return serverList;}

创建ServerList<?>类型的 Bean，用于获取可用的后端服务实例列表。

3. serverIntrospector()方法

    @Beanpublic ServerIntrospector serverIntrospector() {return new EurekaServerIntrospector();}

创建ServerIntrospector类型的 Bean，用于获取服务实例的详细信息。

在该EurekaRibbonClientConfiguration类被初始化完成之后，还会调用preprocess()方法，进行一些预处理的操作。

至此，RibbonEurekaAutoConfiguration自动配置类完成了在Spring容器中的初始化，使得在分布式系统中，Ribbon 和 Eureka 能够协同工作，确保服务的高可用性和可靠性。