(一)项目环境和问题描述

1. 项目环境：

   JDK1.8 + apache-maven-3.3.9 + idea 2018.3

   SpringBoot + SpringCloud + Redis + 分布式微服务架构

2. 需要实现的功能:
   需求：实现redis中央缓存。缓存商品分类的数据。

① redis中央缓存已经搭建完毕，微服务之间是通过Fegin进行调用，创建了一个redis接口（因为此中央缓存是一个公共的服务，很多服务都需要进行调用，所以抽取一个公共 的接口）

② 托底函数 问题就出现在托底函数上面

package cn.lzj.aigou.client;

import feign.hystrix.FallbackFactory;
import org.springframework.stereotype.Component;

/**
 * 托底函数，即回调函数，针对RedisClient
 */
@Component   //交给Spring管理，配置为组件
public class RedisClientFallback implements FallbackFactory<RedisClient> {

    @Override
    public RedisClient create(Throwable throwable) {

        //进行托底方法的业务撰写
        return new RedisClient() {
            @Override
            public void set(String key, String value) {
            }
            @Override
            public String get(String key) {
                return null;   //使用null作为托底数据
            }
        };
    }
}

③ 此时如果客户端要调用已经搭建好的中央缓存服务，如果客户端的服务（即产品分类）开启了熔断支持，产品分类服务就无法进行启动，显示找不到托底函数

错误

错误日志信息：

2019-05-12 10:07:40.201  INFO 14100 --- [           main] ConditionEvaluationReportLoggingListener : 

Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
2019-05-12 10:07:40.255 ERROR 14100 --- [           main] o.s.boot.SpringApplication               : Application run failed

org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'productTypeController': Unsatisfied dependency expressed through field 'productTypeService'; nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'productTypeServiceImpl': Unsatisfied dependency expressed through field 'redisClient'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'cn.lzj.aigou.client.RedisClient': FactoryBean threw exception on object creation; nested exception is java.lang.IllegalStateException: No fallbackFactory instance of type class cn.lzj.aigou.client.RedisClientFallback found for feign client COMMON-PRIVODER
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:586) ~[spring-beans-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:90) ~[spring-beans-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:372) ~[spring-beans-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1341) ~[spring-beans-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:572) ~[spring-beans-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:495) ~[spring-beans-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:317) ~[spring-beans-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) ~[spring-beans-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:315) ~[spring-beans-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199) ~[spring-beans-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:759) ~[spring-beans-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:869) ~[spring-context-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:550) ~[spring-context-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:140) ~[spring-boot-2.0.5.RELEASE.jar:2.0.5.RELEASE]
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:780) [spring-boot-2.0.5.RELEASE.jar:2.0.5.RELEASE]
	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:412) [spring-boot-2.0.5.RELEASE.jar:2.0.5.RELEASE]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:333) [spring-boot-2.0.5.RELEASE.jar:2.0.5.RELEASE]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1277) [spring-boot-2.0.5.RELEASE.jar:2.0.5.RELEASE]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1265) [spring-boot-2.0.5.RELEASE.jar:2.0.5.RELEASE]
	at cn.lzj.aigou.product.ProductServiceApplication8002.main(ProductServiceApplication8002.java:15) [classes/:na]
Caused by: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'productTypeServiceImpl': Unsatisfied dependency expressed through field 'redisClient'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'cn.lzj.aigou.client.RedisClient': FactoryBean threw exception on object creation; nested exception is java.lang.IllegalStateException: No fallbackFactory instance of type class cn.lzj.aigou.client.RedisClientFallback found for feign client COMMON-PRIVODER
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:586) ~[spring-beans-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:90) ~[spring-beans-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:372) ~[spring-beans-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1341) ~[spring-beans-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:572) ~[spring-beans-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:495) ~[spring-beans-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:317) ~[spring-beans-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) ~[spring-beans-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:315) ~[spring-beans-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199) ~[spring-beans-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	at org.springframework.beans.factory.config.DependencyDescriptor.resolveCandidate(DependencyDescriptor.java:251) ~[spring-beans-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1135) ~[spring-beans-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1062) ~[spring-beans-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:583) ~[spring-beans-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	... 19 common frames omitted
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'cn.lzj.aigou.client.RedisClient': FactoryBean threw exception on object creation; nested exception is java.lang.IllegalStateException: No fallbackFactory instance of type class cn.lzj.aigou.client.RedisClientFallback found for feign client COMMON-PRIVODER
	at org.springframework.beans.factory.support.FactoryBeanRegistrySupport.doGetObjectFromFactoryBean(FactoryBeanRegistrySupport.java:178) ~[spring-beans-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	at org.springframework.beans.factory.support.FactoryBeanRegistrySupport.getObjectFromFactoryBean(FactoryBeanRegistrySupport.java:101) ~[spring-beans-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.getObjectForBeanInstance(AbstractBeanFactory.java:1645) ~[spring-beans-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.getObjectForBeanInstance(AbstractAutowireCapableBeanFactory.java:1175) ~[spring-beans-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:257) ~[spring-beans-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199) ~[spring-beans-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	at org.springframework.beans.factory.config.DependencyDescriptor.resolveCandidate(DependencyDescriptor.java:251) ~[spring-beans-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.addCandidateEntry(DefaultListableBeanFactory.java:1322) ~[spring-beans-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.findAutowireCandidates(DefaultListableBeanFactory.java:1288) ~[spring-beans-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1098) ~[spring-beans-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1062) ~[spring-beans-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:583) ~[spring-beans-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	... 32 common frames omitted
Caused by: java.lang.IllegalStateException: No fallbackFactory instance of type class cn.lzj.aigou.client.RedisClientFallback found for feign client COMMON-PRIVODER
	at org.springframework.cloud.openfeign.HystrixTargeter.getFromContext(HystrixTargeter.java:93) ~[spring-cloud-openfeign-core-2.0.1.RELEASE.jar:2.0.1.RELEASE]
	at org.springframework.cloud.openfeign.HystrixTargeter.targetWithFallbackFactory(HystrixTargeter.java:64) ~[spring-cloud-openfeign-core-2.0.1.RELEASE.jar:2.0.1.RELEASE]
	at org.springframework.cloud.openfeign.HystrixTargeter.target(HystrixTargeter.java:53) ~[spring-cloud-openfeign-core-2.0.1.RELEASE.jar:2.0.1.RELEASE]
	at org.springframework.cloud.openfeign.FeignClientFactoryBean.loadBalance(FeignClientFactoryBean.java:223) ~[spring-cloud-openfeign-core-2.0.1.RELEASE.jar:2.0.1.RELEASE]
	at org.springframework.cloud.openfeign.FeignClientFactoryBean.getObject(FeignClientFactoryBean.java:244) ~[spring-cloud-openfeign-core-2.0.1.RELEASE.jar:2.0.1.RELEASE]
	at org.springframework.beans.factory.support.FactoryBeanRegistrySupport.doGetObjectFromFactoryBean(FactoryBeanRegistrySupport.java:171) ~[spring-beans-5.0.9.RELEASE.jar:5.0.9.RELEASE]
	... 43 common frames omitted

跟踪员源码发现这可能是一个底层的原理问题，因为我的托底函数使用的是实现FallbackFactory这个工厂类，可能是一个执行顺序的问题

3. 解决方案
   有两个解决方案，推荐使用第二种
   方案一：在产品分类服务的入口的启动扫描类配置@SpringBootApplication(scanBasePackages = “cn.lzj.aigou.client”)，直接声明扫描对应的接口的包

方案二：托底函数实现自己的接口类，不实现

注意在我们的pom中导入依赖的时候，比如，引入一个jar包，再项目编译之后，这些代码是和我当前写的代码所在的目录是同一个路径

产品服务端的启动类，因为我们使用的是SpringBoot的注解进行扫描的，@SpringBootApplication是扫描当前启动类所在的包的类及其子包的类，当引入的fegin接口和回调函数需要在和启动类平级或在其子包内

之前自己使用实现自己写的fegin接口，配置了熔断机制之后，启动产品分类服务还是现实找不到 回调函数，结果就发现自己的产品的服务端的入口类的包结构多了一层product，结果在编译的时候，fegin接口就是在入口类的父包的子包内。于是就找不到。。。。。这是一个坑。。。。以后注意（归根结底，还是对Springcloud的原理没有理解透彻，慢慢积累吧）

Fegin接口及其托底函数，需要和启动类平级或为其子包的类