SpringCloudfeign的配置加载

     spring cloud feign我们使用 @FeignClient注解，其中有几个核心属性：

@AliasFor("name")
String value() default "";

@Deprecated
String serviceId() default "";

/**
 * This will be used as the bean name instead of name if present, but will not be used as a service id.这个注释我理解的似乎有点问题，不知道理解的对不对
 */
String contextId() default "";

@AliasFor("value")
String name() default "";

String qualifier() default "";

　　

spring会用FeignClientsRegistrar这个类注册当前client，其中有一个很重要的属性就是clientName，因为clientName会影响到我们配置该client，clientName的定义看下面代码，可以看到contextId的优先级最高，当你定义了contextId后clientName取的就是contextId。

org.springframework.cloud.openfeign.FeignClientsRegistrar.getClientName

private String getClientName(Map<String, Object> client) {
   if (client == null) {
      return null;
   }
   String value = (String) client.get("contextId");//可以看到contextId的优先级最高>value>name>serviceId
   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());
}

其中有一个很容易搞错的问题，就是client beanName(区别于clientName),首先看出qualifier的级别最高，如果没有定义qualifier但定义了contextId后实际的bean名称是contextId+"FeignClient"

org.springframework.cloud.openfeign.FeignClientsRegistrar.registerFeignClient

String alias = contextId + "FeignClient";//拼接了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)) {//如果有qualifier就用qualifier
   alias = qualifier;
}

但是FeignClient注解contextId源码中的注释 This will be used as the bean name instead of name if present, but will not be used as a service id.我理解起来这个注释有点问题 

spring cloud feign的配置都是基于clientName来识别的,例如

   feign.client.clientName.connect-timeout=100

相关配置会被装载到FeignClientProperties，其中支持配置的属性如图

 最终通过FeignClientFactoryBean将FeignClientProperties中相应client的配置装配到feignclient中，核心方法为

org.springframework.cloud.openfeign.FeignClientFactoryBean.configureFeign

protected void configureFeign(FeignContext context, Feign.Builder builder) {
   FeignClientProperties properties = applicationContext.getBean(FeignClientProperties.class);
   if (properties != null) {
      if (properties.isDefaultToProperties()) {
          //三种配置依次装载
         configureUsingConfiguration(context, builder);//先配置Java代码中的配置
         configureUsingProperties(properties.getConfig().get(properties.getDefaultConfig()), builder);//配置文件中的默认配置
         configureUsingProperties(properties.getConfig().get(this.contextId), builder);//配置了clientName的配置
      } else {
         configureUsingProperties(properties.getConfig().get(properties.getDefaultConfig()), builder);
         configureUsingProperties(properties.getConfig().get(this.contextId), builder);
         configureUsingConfiguration(context, builder);
      }
   } else {
      configureUsingConfiguration(context, builder);
   }
}