java注解@FeignClient修饰的类路径不在spring boot入口类所在的包下，有哪几种处理方式？

一、注解@EnableFeignClients

修饰在spring boot入口类，使得openfeign的@FeignClient注解生效。

我们进一步看看注解@EnableFeignClients的使用方式。

String[] basePackages() default {};Class<?>[] basePackageClasses() default {};Class<?>[] clients() default {};

• 其实已经能满足我们的需求了，但是，很多业务方在引用的时候，往往是懒得去配置。

像下面这样，多写一个配置参数就算输了。

import org.springframework.boot.SpringApplication;
import org.springframework.cloud.client.SpringCloudApplication;
import org.springframework.cloud.openfeign.EnableFeignClients;@SpringCloudApplication
@EnableFeignClients
public class UserServiceApplication {public static void main(String[] args) {SpringApplication.run(UserServiceApplication.class, args);}
}

你本来写好了使用文档，像下面这样使用：

// AuthServiceClient类所在的包名是com.xxx.ddd.jwt.feign
// 当前用户服务的@FeignClient所在包路径是com.xxx.user.service.feign
@SpringCloudApplication
@EnableFeignClients(basePackages = {com.xxx.user.service.feign,com.xxx.ddd.jwt.feign})public class UserServiceApplication {public static void main(String[] args) {SpringApplication.run(UserServiceApplication.class, args);}
}

• 可惜，使用的人，都嫌弃这配置过于多了，压根就不想关心@EnableFeignClients的属性应该写些啥。

所以，本文就简单说下，推荐的一个方式，让使用方不用去关心额外的包路径。

二、类的结构

• com.xxx.ddd.jwt
  • JwtFeignPackageClass.java
  • feign
    • AuthServiceClient.java

保证注解@EnableFeignClients必须攘括了@FeignClient的包路径。

三、AuthServiceClient.java

package com.xxx.ddd.jwt.feign;import org.springframework.cloud.openfeign.FeignClient;@FeignClient(name = "auth-service")
public interface AuthServiceClient {// TODO 写你自己的接口
}

四、JwtFeignPackageClass.java

注意，该类的路径是在@FeignClient的包路径下，或者其上一级包路径。

package com.xxx.ddd.jwt;import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
import org.springframework.cloud.openfeign.EnableFeignClients;/*** jwt feign注解生效的包路径.** @author xxx*/
@EnableFeignClients
public class JwtFeignPackageClass {
}

五、总结

• org.springframework.cloud.openfeign.FeignClientsRegistrar

class FeignClientsRegistrarimplements ImportBeanDefinitionRegistrar, ResourceLoaderAware, EnvironmentAware{}

梳理下它的主要代码

@Overridepublic void registerBeanDefinitions(AnnotationMetadata metadata,BeanDefinitionRegistry registry) {registerDefaultConfiguration(metadata, registry);registerFeignClients(metadata, registry);}

• 扫描注解EnableFeignClients的类所在包下的所有注解FeignClient

	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() {@Overrideprotected 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 interfaceAnnotatedBeanDefinition 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);}}}}

• 拼接对象FeignClientFactoryBean的属性，利用BeanDefinitionReaderUtils.registerBeanDefinition注册到spring容器

	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();beanDefinition.setAttribute(FactoryBean.OBJECT_TYPE_ATTRIBUTE, className);// has a default, won't be nullboolean primary = (Boolean) attributes.get("primary");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);}

openfeign的@FeignClient封装了http请求的入参和出参，并且支持okhttp/httpclient/HttpsURLConnection等调用方式。