1. 错误信息
***************************
APPLICATION FAILED TO START
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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")