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

最新推荐文章于 2023-08-15 09:38:27 发布

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最新推荐文章于 2023-08-15 09:38:27 发布

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文章标签： java springcloud

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在学习Feign+hystrix熔断时遇到启动时的bug，错误显示缺少fallback类实例。问题源于@Component注解未生效，可能是SpringBoot扫描包路径不包括fallback类所在包。解决方案是在启动类上添加@ComponentScan指定包路径，并使用IDEA的Rebuild Project强制重新生成所有classes。

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项目场景：

学习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

Caused by: java.lang.IllegalStateException: No fallback instance of type class org.springblade.demo.feign.BlogClientFallback found for feign client blade-demo
	at org.springblade.core.cloud.sentinel.BladeFeignSentinel$Builder$1.getFromContext(BladeFeignSentinel.java:103)
	at org.springblade.core.cloud.sentinel.BladeFeignSentinel$Builder$1.create(BladeFeignSentinel.java:87)
	at feign.ReflectiveFeign.newInstance(ReflectiveFeign.java:64)
	at feign.Feign$Builder.target(Feign.java:269)
	at org.springframework.cloud.openfeign.HystrixTargeter.target(HystrixTargeter.java:38)
	at org.springframework.cloud.openfeign.HystrixTargeter$$FastClassBySpringCGLIB$$b9e5b0c6.invoke(<generated>)
	at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:218)
	at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:779)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163)
	at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:750)
	at org.springframework.aop.aspectj.MethodInvocationProceedingJoinPoint.proceed(MethodInvocationProceedingJoinPoint.java:88)
	at com.alibaba.cloud.sentinel.feign.SentinelTargeterAspect.process(SentinelTargeterAspect.java:44)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethodWithGivenArgs(AbstractAspectJAdvice.java:644)
	at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethod(AbstractAspectJAdvice.java:633)
	at org.springframework.aop.aspectj.AspectJAroundAdvice.invoke(AspectJAroundAdvice.java:70)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
	at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:750)
	at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:95)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
	at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:750)
	at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:692)
	at org.springframework.cloud.openfeign.HystrixTargeter$$EnhancerBySpringCGLIB$$f66027e.target(<generated>)
	at org.springframework.cloud.openfeign.FeignClientFactoryBean.loadBalance(FeignClientFactoryBean.java:352)
	at org.springframework.cloud.openfeign.FeignClientFactoryBean.getTarget(FeignClientFactoryBean.java:388)
	at org.springframework.cloud.openfeign.FeignClientFactoryBean.getObject(FeignClientFactoryBean.java:361)
	at org.springframework.cloud.openfeign.FeignClientsRegistrar.lambda$registerFeignClient$0(FeignClientsRegistrar.java:246)
	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

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.