FeignClient 报错: A bean with that name has already been defined and overriding is disabled.

1. 错误信息

***************************
APPLICATION FAILED TO START
***************************

Description:

The bean 'xxx.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

2. 原因

多个FeignClient访问同一个目标服务,导致value值相同

@FeignClient(value = "product.center", path = "/info")

而在FeignClient的自动配置类中(FeignClientsRegistrar.class), 注册Bean时,导致BeanName相同,报错

主要方法如下:

	public void registerFeignClients(AnnotationMetadata metadata,
			BeanDefinitionRegistry registry) {
		ClassPathScanningCandidateComponentProvider scanner = getScanner();
		scanner.setResourceLoader(this.resourceLoader);

		Set<String> basePackages;

		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) {
			scanner.addIncludeFilter(annotationTypeFilter);
			basePackages = getBasePackages(metadata);
		}
		else {
			final Set<String> clientClasses = new HashSet<>();
			basePackages = new HashSet<>();
			for (Class<?> clazz : clients) {
				basePackages.add(ClassUtils.getPackageName(clazz));
				clientClasses.add(clazz.getCanonicalName());
			}
			AbstractClassTestingTypeFilter filter = new AbstractClassTestingTypeFilter() {
				@Override
				protected boolean match(ClassMetadata metadata) {
					String cleaned = metadata.getClassName().replaceAll("\\$", ".");
					return clientClasses.contains(cleaned);
				}
			};
			scanner.addIncludeFilter(
					new AllTypeFilter(Arrays.asList(filter, annotationTypeFilter)));
		}

		for (String basePackage : basePackages) {
			Set<BeanDefinition> candidateComponents = scanner
					.findCandidateComponents(basePackage);
			for (BeanDefinition candidateComponent : candidateComponents) {
				if (candidateComponent instanceof AnnotatedBeanDefinition) {
					// verify annotated class is an interface
					AnnotatedBeanDefinition 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);
				}
			}
		}
	}

	private void registerFeignClient(BeanDefinitionRegistry registry,
			AnnotationMetadata annotationMetadata, Map<String, Object> attributes) {
		String className = annotationMetadata.getClassName();
		BeanDefinitionBuilder definition = BeanDefinitionBuilder
				.genericBeanDefinition(FeignClientFactoryBean.class);
		validate(attributes);
		definition.addPropertyValue("url", getUrl(attributes));
		definition.addPropertyValue("path", getPath(attributes));
		String name = getName(attributes);
		definition.addPropertyValue("name", name);
		String contextId = getContextId(attributes);
		definition.addPropertyValue("contextId", contextId);
		definition.addPropertyValue("type", className);
		definition.addPropertyValue("decode404", attributes.get("decode404"));
		definition.addPropertyValue("fallback", attributes.get("fallback"));
		definition.addPropertyValue("fallbackFactory", attributes.get("fallbackFactory"));
		definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE);

		String alias = contextId + "FeignClient";
		AbstractBeanDefinition beanDefinition = definition.getBeanDefinition();

		boolean primary = (Boolean) attributes.get("primary"); // has a default, won't be
																// null

		beanDefinition.setPrimary(primary);

		String qualifier = getQualifier(attributes);
		if (StringUtils.hasText(qualifier)) {
			alias = qualifier;
		}

		BeanDefinitionHolder holder = new BeanDefinitionHolder(beanDefinition, className,
				new String[] { alias });
		BeanDefinitionReaderUtils.registerBeanDefinition(holder, registry);
	}

在registerFeignClients 方法中扫描到指定包下所有的FeignClient, 并在registerFeignClient中构建对应的BeanDefinition对象并注入到容器中,但是这里可以看见, BeanName 是使用的每个FeignClient的类名:

String className = annotationMetadata.getClassName();
//...
BeanDefinitionHolder holder = new BeanDefinitionHolder(beanDefinition, className,
				new String[] { alias });
		BeanDefinitionReaderUtils.registerBeanDefinition(holder, registry);

所以不是FeignClient 本身的问题

但是在registerFeignClients方法中,还有一行代码:

String name = getClientName(attributes);
registerClientConfiguration(registry, name,
							attributes.get("configuration"));

这里注入的是每个FeignClient的自定义configuration(即FeignClient的configuration属性定义的配置类)

此类的名称取法如下:

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());
	}

即可看见,在contextId 属性为空的情况下,不同的FeignClient 类,因为value值相同,所以beanName相同,生成方式如下:

registry.registerBeanDefinition(
				name + "." + FeignClientSpecification.class.getSimpleName(),
				builder.getBeanDefinition());

3. 解决

正如错误提示信息一样, 可以加如下配置:

spring.main.allow-bean-definition-overriding=true

即当名称相同时,则覆盖

这样可以解决问题,并且网上大多数都是这么解决的,但是这样可能会有一些问题:

在上面的分析中, 因为注入每个FeignClient 的 configuration 配置信息类导致的,那么如果配置了可覆盖,那么所有的FeignClient 都是使用同一份配置,在平常使用时,如果没有配置configuration 属性,则没有问题,如果配置了,就不能使用这种方式;

第二,配置全局的可覆盖可能会隐藏简单的,代价小的,在启动时就会报错的问题, 而因为覆盖的原因,导致运行时出现无法追溯的问题;

推荐:

根据源码可以看出,

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());
	}

名称首要取的是contextId属性,如果不为空,,则不会使用value作为名称,所以只需要在value相同的 FeignClient 配置不同的 contextId 即可:

@FeignClient(value = "product.center",contextId="search", path = "/info")