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

java 复制代码

@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

java 复制代码

@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

java 复制代码

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。

ribbonPing(IClientConfig config)方法

java 复制代码

    @Bean
	@ConditionalOnMissingBean
	public 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。

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

java 复制代码

    @Bean
	@ConditionalOnMissingBean
	public 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。

serverIntrospector()方法

java 复制代码

    @Bean
	public 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。