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场景：
因项目需要，一个springcloud微服务工程需要同时部署到A,B两个项目使用，但A项目使用Eureka注册中心，B项目使用Nacos注册中心，现在需要通过部署时修改配置来实现多注册中心的切换。
解决思路：
如果同时引入nacos和eureka的依赖和配置，不做任何处理，会导致启动失败：

***************************
APPLICATION FAILED TO START
***************************Description:Field registration in org.springframework.cloud.client.serviceregistry.ServiceRegistryAutoConfiguration$ServiceRegistryEndpointConfiguration required a single bean, but 2 were found:- nacosRegistration: defined by method 'nacosRegistration' in class path resource [com/alibaba/cloud/nacos/registry/NacosServiceRegistryAutoConfiguration.class]- eurekaRegistration: defined in BeanDefinition defined in class path resource [org/springframework/cloud/netflix/eureka/EurekaClientAutoConfiguration$RefreshableEurekaClientConfiguration.class]Action:Consider marking one of the beans as @Primary, updating the consumer to accept multiple beans, or using @Qualifier to identify the bean that should be consumed

不难看出失败原因是单例bean找到了两个实例，那么该如何解决这个问题呢？首先想到的肯定是删除掉暂时不需要使用的实例（如使用eureka注册中心则删掉引入pom的nacos依赖），这样做是没有问题的，但是维护成本比较高。能不能从springboot自动装配原理入手，找到更便捷的方法呢？接着看：
我们都知道SpringBoot的启动类的@SpringBootApplication是一个组合注解，它里面的@EnableAutoConfiguration会引入AutoConfigurationImportSelector.class


从这个类的方法getAutoConfigurationEntry()一层一层点进去看，

SpringFactoriesLoader.loadFactories()会去检索META-INF/spring.factories文件。

protected List<AutoConfigurationImportFilter> getAutoConfigurationImportFilters() {return SpringFactoriesLoader.loadFactories(AutoConfigurationImportFilter.class, this.beanClassLoader);}

那么思路就比较清晰了，我们可以通过实现AutoConfigurationImportFilter接口，将自己的过滤逻辑写在实现类中，就可以实现自定义的自动装配过滤器了。
上代码：
通过把1、2、3的代码放到一个starter中，然后在具体的项目中引用这个starter，配置文件中添加4的配置就可以切换了，当然具体nacos和eureka在yml中的配置还是分开写，只需指定用那个配置就行
1.过滤器

package com.demo.business;import com.demo.business.constants.RegistrationCenterConstants;
import org.apache.commons.lang3.StringUtils;
import org.springframework.boot.autoconfigure.AutoConfigurationImportFilter;
import org.springframework.boot.autoconfigure.AutoConfigurationMetadata;
import org.springframework.context.EnvironmentAware;
import org.springframework.core.env.Environment;public class EngineAutoConfigurationImportFilter implements AutoConfigurationImportFilter, EnvironmentAware {private Environment environment;@Overridepublic boolean[] match(String[] autoConfigurationClasses, AutoConfigurationMetadata autoConfigurationMetadata) {//获取配置的注册中心，默认为nacosString registryType = environment.getProperty("registry.type", RegistrationCenterConstants.NACOS);boolean[] match = new boolean[autoConfigurationClasses.length];//当自定义标识为eureka，则排除nacos的自动装配，反之同理；if (registryType.equals(RegistrationCenterConstants.EUREKA)) {for (int i = 0; i < autoConfigurationClasses.length; i++) {match[i] = !StringUtils.isNotBlank(autoConfigurationClasses[i]) ||!autoConfigurationClasses[i].equals(RegistrationCenterConstants.NACOS_SERVICE_REGISTRY_AUTO_CONFIGURATION);}} else {for (int i = 0; i < autoConfigurationClasses.length; i++) {if (StringUtils.isNotBlank(autoConfigurationClasses[i])){match[i] = !RegistrationCenterConstants.EUREKA_DISCOVERY_CLIENT_CONFIGURATION.equals(autoConfigurationClasses[i])&& !RegistrationCenterConstants.EUREKA_AUTO_CONFIGURATION_CLASSES.equals(autoConfigurationClasses[i]);}}}return match;}@Overridepublic void setEnvironment(Environment environment) {this.environment = environment;}
}或者以下这样也可以
import org.apache.commons.lang3.StringUtils;
import org.springframework.boot.autoconfigure.AutoConfigurationImportFilter;
import org.springframework.boot.autoconfigure.AutoConfigurationMetadata;
import org.springframework.context.EnvironmentAware;
import org.springframework.core.env.Environment;public class EngineAutoConfigurationImportFilter implements AutoConfigurationImportFilter, EnvironmentAware {private Environment environment;public EngineAutoConfigurationImportFilter() {}public boolean[] match(String[] autoConfigurationClasses, AutoConfigurationMetadata autoConfigurationMetadata) {String registryType = this.environment.getProperty("registry.type", "eureka");boolean[] match = new boolean[autoConfigurationClasses.length];//提取成常量String prefix = registryType.equals("nacos") ? "org.springframework.cloud.netflix.eureka" : "com.alibaba.cloud.nacos";for(int i = 0; i < autoConfigurationClasses.length; ++i) {if (StringUtils.isNotBlank(autoConfigurationClasses[i])) {match[i] = !autoConfigurationClasses[i].startsWith(prefix);}}return match;}public void setEnvironment(Environment environment) {this.environment = environment;}
}

2.常量类

package com.demo.business.constants;/*** 注册中心相关常量类*/
public class RegistrationCenterConstants {public static final String NACOS = "nacos";public static final String EUREKA = "eureka";public static final String EUREKA_AUTO_CONFIGURATION_CLASSES = "org.springframework.cloud.netflix.eureka.EurekaClientAutoConfiguration";public static final String EUREKA_DISCOVERY_CLIENT_CONFIGURATION = "org.springframework.cloud.netflix.eureka.EurekaDiscoveryClientConfiguration";public static final String NACOS_SERVICE_REGISTRY_AUTO_CONFIGURATION = "com.alibaba.cloud.nacos.registry.NacosServiceRegistryAutoConfiguration";或者
public static final String NACOS_PREFIX = "com.alibaba.cloud.nacos";public static final String EUREKA_PREFIX = "org.springframework.cloud.netflix.eureka";}

3.spring.factories文件(注意路径一定要在META-INF包下)

org.springframework.boot.autoconfigure.AutoConfigurationImportFilter=\com.example.demo.business.EngineAutoConfigurationImportFilter

4.配置文件添加

registry:type: nacos

效果
通过修改配置项registry.type就可以实现eureka和nacos的切换了