@FeignClient注解中属性contextId的使用说明

2022-11-13 10:11:59 注解属性使用说明

一、概述

如果我们使用Feign定义了两个接口，但是目标服务是同一个，那么在SpringBoot启动时就会遇到一个问题：

Description:
The bean 'xxxxxxxx.FeignClientSpecification', defined in null, could not be reGIStered. A bean with that name has already been defined in null and overriding is disabled.
Action:
Consider renaming one of the beans or enabling overriding by setting spring.main.allow-bean-definition-overriding=true

二、解决方案

2.1 方案1

修改yml配置：spring.main.allow-bean-definition-overriding=true

spring:
  main:
    allow-bean-definition-overriding: true

2.2 方案2

在每个Feign的接口中，在注解上加 contextId属性

contextId在Feign Client的作用是在注册Feign Client Configuration的时候需要一个名称，名称是通过getClientName方法获取的

@FeignClient(name = "sale-service",contextId= "saleservice1")
 
public interface saleClient{
 
    @RequestMapping(value = "/sale/add", method = RequestMethod.GET)
 
    String add(@RequestParam("saleNum") String queryStr);
 
}

备注：contextId= "名称" 中的名称，不能用“_”会报错，可以用“-”

三、源代码分析

包名：spring-cloud-openfeign-core-2.2.5.RELEASE.jar
类路径：org.springframework.cloud.openfeign.FeignClientsRegistrar

相关代码1

 private void registerFeignClient(BeanDefinitionRegistry registry, AnnotationMetadata annotationMetadata, Map<String, Object> attributes) {
        String className = annotationMetadata.getClassName();
        BeanDefinitionBuilder definition = BeanDefinitionBuilder.genericBeanDefinition(FeignClientFactoryBean.class);
        this.validate(attributes);
        definition.addPropertyValue("url", this.getUrl(attributes));
        definition.addPropertyValue("path", this.getPath(attributes));
        String name = this.getName(attributes);
        definition.addPropertyValue("name", name);
        String contextId = this.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(2);
        String alias = contextId + "FeignClient";
        AbstractBeanDefinition beanDefinition = definition.getBeanDefinition();
        beanDefinition.setAttribute("factoryBeanObjectType", className);
        boolean primary = (Boolean)attributes.get("primary");
        beanDefinition.setPrimary(primary);
        String qualifier = this.getQualifier(attributes);
        if (StringUtils.hasText(qualifier)) {
            alias = qualifier;
        }
 
        BeanDefinitionHolder holder = new BeanDefinitionHolder(beanDefinition, className, new String[]{alias});
        BeanDefinitionReaderUtils.registerBeanDefinition(holder, registry);
    }

代码截图：

相关代码2

可以看到, name应该是从注解中的属性取值来的, 再看看getClientName()方法.

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