Spring Cloud踩坑（三）添加了Fallback以后No fallback instance of type ... found for feign client

你的名字 2022-03-09 05:36 767阅读 0赞

题记：我遇到的问题在上一篇解决方案中，这个有待回看，但是感觉挺有道理，临时准载下来！

## 问题 ##

### No fallback instance of type ... found for feign client ###

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'orderProcessorBiz': 
     
     Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: 
     Could not autowire field:  private com.xx.xx.service.IRemoteBridgeService com.xx.xx.biz.order.OrderProcessorBiz.remoteBridgeService; 
     
     nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'com.xx.xx.service.IRemoteBridgeService': 
     
     FactoryBean threw exception on object creation; nested exception is java.lang.IllegalStateException: 
     No fallback instance of type class com.xx.xx.HystrixClientFallback found for feign client http://172.16.2.163:8001 
        
    Caused by: java.lang.IllegalStateException: No fallback instance of type class com.xx.xx.HystrixClientFallback found for feign client http://172.16.2.163:8001

### 通常需要确认配置内容 ###

1.  开启hystrix

feign.hystrix.enabled=true

1.  Fallback类需要注解`@Component`

### 依旧不行？ ###

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。

@EnableAspectJAutoProxy(proxyTargetClass = true)

这里给一个链接：  
[https://stackoverflow.com/questions/33110661/spring-aop-bean-injection-bug][https_stackoverflow.com_questions_33110661_spring-aop-bean-injection-bug]

### 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);
    
    ......
    
    //以下代码省略

问题出现在isTypeMatch

![Image 1][]

isTypeMatch.png

这里isTypeMatch 返回了false，因为骗不过JVM类型检查。当使用cglib则是匹配的。

原文：https://www.jianshu.com/p/c8210d878e96

[https_stackoverflow.com_questions_33110661_spring-aop-bean-injection-bug]: https://link.jianshu.com?t=https%3A%2F%2Fstackoverflow.com%2Fquestions%2F33110661%2Fspring-aop-bean-injection-bug
[Image 1]: