No fallback instance of type class错误的解决方案

项目场景

feign+hystrix熔断进行远程调用

问题描述

启动远程调用类时会出现bug

2023-09-17 17:05:21.017 [main] ERROR o.s.boot.SpringApplication - Application run failed
org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'wmNewsAutoScanServiceImpl': Unsatisfied dependency expressed through field 'articleClient'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'com.itheima.apis.article.IArticleClient': Unexpected exception during bean creation; nested exception is java.lang.IllegalStateException: No fallback instance of type class com.itheima.apis.article.fallback.IArticleClientFallback found for feign client leadnews-article
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.resolveFieldValue(AutowiredAnnotationBeanPostProcessor.java:660)
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:640)
	at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:119)
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessProperties(AutowiredAnnotationBeanPostProcessor.java:399)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1425)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:593)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:516)
	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:324)
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234)
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:322)
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:897)
	at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:879)
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:551)
	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:143)
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:758)
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:750)
	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:405)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:315)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1237)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1226)
	at com.heima.wemedia.WemediaApplication.main(WemediaApplication.java:22)
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'com.itheima.apis.article.IArticleClient': Unexpected exception during bean creation; nested exception is java.lang.IllegalStateException: No fallback instance of type class com.itheima.apis.article.fallback.IArticleClientFallback found for feign client leadnews-article
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:529)
	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:324)
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234)
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:322)
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202)
	at org.springframework.beans.factory.config.DependencyDescriptor.resolveCandidate(DependencyDescriptor.java:276)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1307)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1227)
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.resolveFieldValue(AutowiredAnnotationBeanPostProcessor.java:657)
	... 21 common frames omitted
Caused by: java.lang.IllegalStateException: No fallback instance of type class com.itheima.apis.article.fallback.IArticleClientFallback found for feign client leadnews-article
	at org.springframework.cloud.openfeign.HystrixTargeter.getFromContext(HystrixTargeter.java:81)
	at org.springframework.cloud.openfeign.HystrixTargeter.targetWithFallback(HystrixTargeter.java:72)
	at org.springframework.cloud.openfeign.HystrixTargeter.target(HystrixTargeter.java:49)
	at org.springframework.cloud.openfeign.FeignClientFactoryBean.loadBalance(FeignClientFactoryBean.java:338)
	at org.springframework.cloud.openfeign.FeignClientFactoryBean.getTarget(FeignClientFactoryBean.java:369)
	at org.springframework.cloud.openfeign.FeignClientFactoryBean.getObject(FeignClientFactoryBean.java:347)
	at org.springframework.cloud.openfeign.FeignClientsRegistrar.lambda$registerFeignClient$0(FeignClientsRegistrar.java:240)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.obtainFromSupplier(AbstractAutowireCapableBeanFactory.java:1235)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1177)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:556)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:516)
	... 29 common frames omitted
2023-09-17 17:05:21.018 [Thread-5] WARN  c.a.n.c.http.HttpClientBeanHolder - [HttpClientBeanHolder] Start destroying common HttpClient
2023-09-17 17:05:21.018 [Thread-5] WARN  c.a.n.c.http.HttpClientBeanHolder - [HttpClientBeanHolder] Destruction of the end

原因分析：

看错误报告是没有fallback类的实例
所以首先需要在fallback类上加上@component注解，让spring生成一个bean。
如果添加@Component都无效，其实不是无效，只是扫描的包的路径不一样，如果我们自定义了自己的业务模块，命名不叫这个，那么配了@Component注解的fallback实例也是扫描不到的。因为SpringBoot默认扫描Application同级目录下的所有包。但是业务模块的包名不一致。

解决方案：

在远程调用启动类上面加上@ComponentScan(“xxx”)注解，
并且使用idea的Build > Rebuild Project, 而不是平时用的Build Project(Ctrl + F9), 可以解决问题. 原因是, Build只会编译被修改了的文件, 但这次, 涉及注解里的内容, 需要强行把所有的classes重新生成. 只有Rebuild Project才有这个效果.