@FeignClient注解中属性 contextId使用

谁借莪１个温暖的怀抱￠ 2022-10-16 05:59 140阅读 0赞

# 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：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2xhenljaGVlcnVw_size_16_color_FFFFFF_t_70][]

## 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());
                }
            }
        }

代码截图：![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2xhenljaGVlcnVw_size_16_color_FFFFFF_t_70 1][]

> 一目了然了, 我们声明`@FeignClient`注解时, 只使用了`value`属性, 所以产生了冲突, 只要加上`contextId`就好了.

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