前言

前段时间业务部门有这么一个业务场景，他们自己微服务注册中心是用eureka，他们有一些服务接口要调用兄弟部门的接口，他们定了一个服务调用方案，业务部门直接把他们服务注册到兄弟部门的注册中心，然后走rpc调用，兄弟部门注册中心是用nacos。

一开始业务部门研发直接在在pom.xml这么引入

    <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
        </dependency>

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

然后项目启动报了如下错

Field registration in org.springframework.cloud.client.serviceregistry.ServiceRegistryAutoConfiguration$ServiceRegistryEndpointConfiguration required a single bean, but 2 were found:
	- nacosRegistration: defined by method 'nacosRegistration' in class path resource [com/alibaba/cloud/nacos/NacosDiscoveryAutoConfiguration.class]
	- eurekaRegistration: defined in BeanDefinition defined in class path resource [org/springframework/cloud/netflix/eureka/EurekaClientAutoConfiguration$RefreshableEurekaClientConfiguration.class]

业务部门是这么解决的，每次发版时，如果是要纳入兄弟部门的微服务，他们就先手动注释掉eureka的客户端依赖。

后来业务部门就向我们部门提了一个需求，pom引入多个注册中心客户端，项目也要能正常启动

需求分析

从项目异常分析

Field registration in org.springframework.cloud.client.serviceregistry.ServiceRegistryAutoConfiguration$ServiceRegistryEndpointConfiguration required a single bean, but 2 were found:
	- nacosRegistration: defined by method 'nacosRegistration' in class path resource [com/alibaba/cloud/nacos/NacosDiscoveryAutoConfiguration.class]
	- eurekaRegistration: defined in BeanDefinition defined in class path resource [org/springframework/cloud/netflix/eureka/EurekaClientAutoConfiguration$RefreshableEurekaClientConfiguration.class]

可以看出springcloud默认的服务注册是只支持单服务注册中心。因此我们解决的方案要么扩展springcloud源码，让它支持多注册中心，要么就是告诉springcloud当存在多种注册中心客户端时，选择一种我们想要的注册中心客户端

本文就选实现相对容易的方案，当存在多种注册中心客户端时，我们告诉springcloud，我们想选的注册中心

实现方案

目前基本只要和springboot集成的开源项目，可以说大部分使用了自动装配，因此我们的解决思路也是从自动装配搞起

前置知识

protected AutoConfigurationEntry getAutoConfigurationEntry(AutoConfigurationMetadata autoConfigurationMetadata,
			AnnotationMetadata annotationMetadata) {
		if (!isEnabled(annotationMetadata)) {
			return EMPTY_ENTRY;
		}
		AnnotationAttributes attributes = getAttributes(annotationMetadata);
		List<String> configurations = getCandidateConfigurations(annotationMetadata, attributes);
		configurations = removeDuplicates(configurations);
		Set<String> exclusions = getExclusions(annotationMetadata, attributes);
		checkExcludedClasses(configurations, exclusions);
		configurations.removeAll(exclusions);
		configurations = filter(configurations, autoConfigurationMetadata);
		fireAutoConfigurationImportEvents(configurations, exclusions);
		return new AutoConfigurationEntry(configurations, exclusions);
	}

	private List<String> filter(List<String> configurations, AutoConfigurationMetadata autoConfigurationMetadata) {
		long startTime = System.nanoTime();
		String[] candidates = StringUtils.toStringArray(configurations);
		boolean[] skip = new boolean[candidates.length];
		boolean skipped = false;
		for (AutoConfigurationImportFilter filter : getAutoConfigurationImportFilters()) {
			invokeAwareMethods(filter);
			boolean[] match = filter.match(candidates, autoConfigurationMetadata);
			for (int i = 0; i < match.length; i++) {
				if (!match[i]) {
					skip[i] = true;
					candidates[i] = null;
					skipped = true;
				}
			}
		}
		if (!skipped) {
			return configurations;
		}
		List<String> result = new ArrayList<>(candidates.length);
		for (int i = 0; i < candidates.length; i++) {
			if (!skip[i]) {
				result.add(candidates[i]);
			}
		}
		if (logger.isTraceEnabled()) {
			int numberFiltered = configurations.size() - result.size();
			logger.trace("Filtered " + numberFiltered + " auto configuration class in "
					+ TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - startTime) + " ms");
		}
		return new ArrayList<>(result);
	}

这两个代码片段，一个是自动装配的代码片段，一个是过滤候选哪些不需要进行自动装配

方案一：利用AutoConfigurationImportFilter + 自定义标识

实现的原理： 当自定的标识为nacos，通过AutoConfigurationImportFilter排除eureka的自动装配；反之排除nacos的自动装配

1、核心实现

public class RegistrationCenterAutoConfigurationImportFilter implements AutoConfigurationImportFilter, EnvironmentAware {

    private Environment environment;

    /**
     * 因为springboot自动装配，默认会把spring.factories的配置的类先全部加载到候选集合中，
     * 因此当我们代码配置启用nacos，则需把其他注册中心，比如eureka先从候选集合排除
     * @param autoConfigurationClasses
     * @param autoConfigurationMetadata
     * @return
     */
    @Override
    public boolean[] match(String[] autoConfigurationClasses, AutoConfigurationMetadata autoConfigurationMetadata) {
        Set<String> activeProfiles = Arrays.stream(environment.getActiveProfiles()).collect(Collectors.toSet());

        if(activeProfiles.contains(RegistrationCenterConstants.ACTIVE_PROFILE_NACOS)){
            return excludeMissMatchRegistrationAutoConfiguration(autoConfigurationClasses, new String[]{RegistrationCenterConstants.EUREKA_AUTO_CONFIGURATION_CLASSES});

        }else if (activeProfiles.contains(RegistrationCenterConstants.ACTIVE_PROFILE_EUREKA)){
            return excludeMissMatchRegistrationAutoConfiguration(autoConfigurationClasses, new String[]{RegistrationCenterConstants.NACOS_DISCOVERY_AUTO_CONFIGURATION_CLASSES,RegistrationCenterConstants.NACOS_DISCOVERY_CLIENT_AUTO_CONFIGURATION_CLASSES,RegistrationCenterConstants.NACOS_DISCOVERY_ENDPOINT_AUTO_CONFIGURATION_CLASSES});
        }


        return new boolean[0];
    }

    private boolean[] excludeMissMatchRegistrationAutoConfiguration(String[] autoConfigurationClasses,String[] needExcludeRegistrationAutoConfigurationClasse) {
        Map<String,Boolean> needExcludeRegistrationAutoConfigurationClzMap = initNeedExcludeRegistrationAutoConfigurationClzMap(needExcludeRegistrationAutoConfigurationClasse);
        boolean[] match = new boolean[autoConfigurationClasses.length];
        for (int i = 0; i < autoConfigurationClasses.length; i++) {
            String autoConfigurationClz = autoConfigurationClasses[i];
            match[i] = !needExcludeRegistrationAutoConfigurationClzMap.containsKey(autoConfigurationClz);

        }

        return match;
    }

    private Map<String,Boolean> initNeedExcludeRegistrationAutoConfigurationClzMap(String[] needExcludeRegistrationAutoConfigurationClasse){
        Map<String,Boolean> needExcludeRegistrationAutoConfigurationClzMap = new HashMap<>();
        for (String needExcludeRegistrationAutoConfigurationClz : needExcludeRegistrationAutoConfigurationClasse) {
            needExcludeRegistrationAutoConfigurationClzMap.put(needExcludeRegistrationAutoConfigurationClz,false);
        }

        return needExcludeRegistrationAutoConfigurationClzMap;

    }

    @Override
    public void setEnvironment(Environment environment) {
         this.environment = environment;
    }


}

2、配置spring.factories

org.springframework.boot.autoconfigure.AutoConfigurationImportFilter=\
com.github.lybgeek.registration.autoconfigure.filter.RegistrationCenterAutoConfigurationImportFilter

方案二：利用application-${指定注册中心标识} + spring.profiles.active

1、在要激活的注册中心的文件禁用其他注册中心客户端

比如appliication-nacos.yml禁用eureka

spring:
  cloud:
    nacos:
      discovery:
        server-addr: localhost:8848

# 禁用eureka客户端自动注册
eureka:
  client:
    enabled: false

2、激活想要注册的注册中心

spring:
  application:
    name: springboot-registration-client
  profiles:
    active: nacos

总结

这两种方案个人是比较推荐方案二，因为改动最小。方案一比较适用于没有提供是否需要激活注册中心开关的注册中心。其次如果我们要排除某些开源自动装配的组件，也可以考虑用方案一

demo链接

https://github.com/lyb-geek/springboot-learning/tree/master/springboot-registrationcenter-switch