No fallback instance of type class found for feign client user-service（转）

1、错误日志

在 feign 开启熔断，配置 fallback 类，实现当前接口的实现类时，报错信息如下：

Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
ERROR 7204 --- [ main] o.s.boot.SpringApplication  : Application run failed
org.springframework.beans.factory.UnsatisfiedDependencyException: 
　　Error creating bean with name 'consumerController': 
Unsatisfied dependency expressed through field 'mUserClient'; 
nested exception is org.springframework.beans.factory.BeanCreationException: 
　　Error creating bean with name 'club.sscai.consumer.client.UserClient': 
FactoryBean threw exception on object creation; 
nested exception is java.lang.IllegalStateException: 
　　No fallback instance of type class club.sscai.consumer.client.UserClientImpl found for feign client user-service

2、通常配置

1、开启 hystrix（默认是关闭的）：feign.hystrix.enabled=true2、Fallback 接口实现类需要注解 @Component

如果到此处还没有解决的话？请往下看。

3、转载解决方案

跟踪代码发现是因为对FeignClient 这个接口做了AOP切面。

@Pointcut("execution(* com.xx.xx.service.IR*.*(..))")
public void remoteCall() {
}

Trace日志看到这么一行：

[DEBUG] [17:50:22.410][JdkDynamicAopProxy][117]:
Creating JDK dynamic proxy: target source is SingletonTargetSource for target object [com.xx.xx.service.HystrixClientFallback@32354b00]

然后考虑是不是因为Spring AOP动态代理默认为 JDK动态代理。

切面还是要切的，Fallback也不能放弃。因为调用的是接口，无论如何都要被切。

换成cglib后，问题成功解决。

原理
SpringAOP 的动态代理有两种实现，JDK动态代理，和Cglib。
Spring默认使用 JDK动态代理。
当类至少实现了一个接口时，使用JDK动态代理。上文的Feign的Fallback类正好是这样。
至于究竟为什么cglib可以成功，就不去深究了，方案就两个，非此即彼。
至于为什么找不到 fallback instance？

private String[] doGetBeanNamesForType(ResolvableType type, boolean includeNonSingletons, boolean allowEagerInit) {List<String> result = new ArrayList<String>();// Check all bean definitions.for (String beanName : this.beanDefinitionNames) {// Only consider bean as eligible if the bean name// is not defined as alias for some other bean.if (!isAlias(beanName)) {try {RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);// Only check bean definition if it is complete.if (!mbd.isAbstract() && (allowEagerInit ||((mbd.hasBeanClass() || !mbd.isLazyInit() || isAllowEagerClassLoading())) &&!requiresEagerInitForType(mbd.getFactoryBeanName()))) {// In case of FactoryBean, match object created by FactoryBean.boolean isFactoryBean = isFactoryBean(beanName, mbd);boolean matchFound = (allowEagerInit || !isFactoryBean || containsSingleton(beanName)) &&(includeNonSingletons || isSingleton(beanName)) && isTypeMatch(beanName, type);......