【OpenFeign】XXX.FeignClientSpecification错误解决与分析

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在一个项目中，如果有多个FeignClient客户端指向同一个微服务，项目启动的过程中可能会抛出如下的异常The bean 'xxx.FeignClientSpecification' could not be registered. A bean with that name has already been defined and overriding is disabled.。

具体异常如下：

***************************
APPLICATION FAILED TO START
***************************Description:The bean 'order-service.FeignClientSpecification' could not be registered. A bean with that name has already been defined and overriding is disabled.Action:Consider renaming one of the beans or enabling overriding by setting spring.main.allow-bean-definition-overriding=true

解决方法

方法一

按照异常的提示在配置文件中添加如下配置：

# application.yml文件
spring:main:allow-bean-definition-overriding: true

方法二

在@FeignClient注解里面添加contextId属性，并保证两个客户端中的contextId属性不一致：

@FeignClient(value = "order-service", path = "/order", contextId = "order1")
public interface OrderClient {
}@FeignClient(value = "order-service", path = "/order", contextId = "order2")
public interface OrderClient {
}

从源码分析原因

@EnableFeignClients注解

在项目的启动类上有一个@EnableFeignClients注解：

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
@Import(FeignClientsRegistrar.class)
public @interface EnableFeignClients {

FeignClientsRegistrar类

FeignClientsRegistrar类会在项目启动过程中注入一些BeanDefinition：

public void registerBeanDefinitions(AnnotationMetadata metadata,BeanDefinitionRegistry registry) {registerDefaultConfiguration(metadata, registry);registerFeignClients(metadata, registry);
}

registerFeignClients()

registerFeignClients()通过扫描带有@FeignClient注解的类，为每个带有@FeignClient注解的类向Spring容器中注入两个BeanDefinition：

FeignClientSpecification
FeignClientFactoryBean

public void registerFeignClients(AnnotationMetadata metadata,BeanDefinitionRegistry registry) {LinkedHashSet<BeanDefinition> candidateComponents = new LinkedHashSet<>();Map<String, Object> attrs = metadata.getAnnotationAttributes(EnableFeignClients.class.getName());AnnotationTypeFilter annotationTypeFilter = new AnnotationTypeFilter(FeignClient.class);final Class<?>[] clients = attrs == null ? null: (Class<?>[]) attrs.get("clients");if (clients == null || clients.length == 0) {ClassPathScanningCandidateComponentProvider scanner = getScanner();scanner.setResourceLoader(this.resourceLoader);scanner.addIncludeFilter(new AnnotationTypeFilter(FeignClient.class));Set<String> basePackages = getBasePackages(metadata);for (String basePackage : basePackages) {candidateComponents.addAll(scanner.findCandidateComponents(basePackage));}}else {for (Class<?> clazz : clients) {candidateComponents.add(new AnnotatedGenericBeanDefinition(clazz));}}for (BeanDefinition candidateComponent : candidateComponents) {if (candidateComponent instanceof AnnotatedBeanDefinition) {// verify annotated class is an interfaceAnnotatedBeanDefinition beanDefinition = (AnnotatedBeanDefinition) candidateComponent;AnnotationMetadata annotationMetadata = beanDefinition.getMetadata();Assert.isTrue(annotationMetadata.isInterface(),"@FeignClient can only be specified on an interface");Map<String, Object> attributes = annotationMetadata.getAnnotationAttributes(FeignClient.class.getCanonicalName());String name = getClientName(attributes);registerClientConfiguration(registry, name,attributes.get("configuration"));registerFeignClient(registry, annotationMetadata, attributes);}}
}

getClientName()

FeignClientSpecification在Spring容器中beanName通过注解中的属性来决定：

private String getClientName(Map<String, Object> client) {if (client == null) {return null;}String value = (String) client.get("contextId");if (!StringUtils.hasText(value)) {value = (String) client.get("value");}if (!StringUtils.hasText(value)) {value = (String) client.get("name");}if (!StringUtils.hasText(value)) {value = (String) client.get("serviceId");}if (StringUtils.hasText(value)) {return value;}throw new IllegalStateException("Either 'name' or 'value' must be provided in @"+ FeignClient.class.getSimpleName());
}