背景

微服务项目要整合合并，结果各种踩坑

问题描述

合并后的项目启动应用报错类型不一致，堆栈如下：

2020-07-02 11:32:04,008 ERROR  [main] org.springframework.boot.SpringApplication:: Application startup failedorg.springframework.beans.factory.BeanCreationException: Error creating bean with name 'CNGetPakgOverDistanceHandler': Injection of resource dependencies failed; nested exception is org.springframework.beans.factory.BeanNotOfRequiredTypeException: Bean named 'stringRedisTemplate' is expected to be of type 'org.springframework.data.redis.core.StringRedisTemplate' but was actually of type 'org.springframework.data.redis.core.RedisTemplate'at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.postProcessPropertyValues(CommonAnnotationBeanPostProcessor.java:321) ~[spring-context-4.3.20.RELEASE.jar:4.3.20.RELEASE]at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1269) ~[spring-beans-4.3.20.RELEASE.jar:4.3.20.RELEASE]at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:551) ~[spring-beans-4.3.20.RELEASE.jar:4.3.20.RELEASE]at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:481) ~[spring-beans-4.3.20.RELEASE.jar:4.3.20.RELEASE]at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:312) ~[spring-beans-4.3.20.RELEASE.jar:4.3.20.RELEASE]at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230) ~[spring-beans-4.3.20.RELEASE.jar:4.3.20.RELEASE]at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:308) ~[spring-beans-4.3.20.RELEASE.jar:4.3.20.RELEASE]at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197) ~[spring-beans-4.3.20.RELEASE.jar:4.3.20.RELEASE]at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:761) ~[spring-beans-4.3.20.RELEASE.jar:4.3.20.RELEASE]at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:867) ~[spring-context-4.3.20.RELEASE.jar:4.3.20.RELEASE]at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:543) ~[spring-context-4.3.20.RELEASE.jar:4.3.20.RELEASE]at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.refresh(EmbeddedWebApplicationContext.java:122) ~[spring-boot-1.5.17.RELEASE.jar:1.5.17.RELEASE]at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:693) ~[spring-boot-1.5.17.RELEASE.jar:1.5.17.RELEASE]at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:360) ~[spring-boot-1.5.17.RELEASE.jar:1.5.17.RELEASE]at org.springframework.boot.SpringApplication.run(SpringApplication.java:303) ~[spring-boot-1.5.17.RELEASE.jar:1.5.17.RELEASE]at com.dianwoba.wireless.fundamental.boot.WirelessSpringApplication.run(WirelessSpringApplication.java:16) ~[wireless-fundamental-1.0.0-20191205.115817-28.jar:1.0.0-SNAPSHOT]at com.dianwoba.order.foul.Application.main(Application.java:20) ~[classes/:?]at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_131]at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_131]at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_131]at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_131]at com.intellij.rt.execution.CommandLineWrapper.main(CommandLineWrapper.java:64) ~[?:?]Caused by: org.springframework.beans.factory.BeanNotOfRequiredTypeException: Bean named 'stringRedisTemplate' is expected to be of type 'org.springframework.data.redis.core.StringRedisTemplate' but was actually of type 'org.springframework.data.redis.core.RedisTemplate'at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:384) ~[spring-beans-4.3.20.RELEASE.jar:4.3.20.RELEASE]at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202) ~[spring-beans-4.3.20.RELEASE.jar:4.3.20.RELEASE]at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.autowireResource(CommonAnnotationBeanPostProcessor.java:522) ~[spring-context-4.3.20.RELEASE.jar:4.3.20.RELEASE]at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.getResource(CommonAnnotationBeanPostProcessor.java:496) ~[spring-context-4.3.20.RELEASE.jar:4.3.20.RELEASE]at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor$ResourceElement.getResourceToInject(CommonAnnotationBeanPostProcessor.java:627) ~[spring-context-4.3.20.RELEASE.jar:4.3.20.RELEASE]at org.springframework.beans.factory.annotation.InjectionMetadata$InjectedElement.inject(InjectionMetadata.java:171) ~[spring-beans-4.3.20.RELEASE.jar:4.3.20.RELEASE]at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:87) ~[spring-beans-4.3.20.RELEASE.jar:4.3.20.RELEASE]at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.postProcessPropertyValues(CommonAnnotationBeanPostProcessor.java:318) ~[spring-context-4.3.20.RELEASE.jar:4.3.20.RELEASE]... 21 more复制代码

查看发现项目中使用的自定义的redis模板定义，代码如下CacheConfig：

@Beanpublic RedisTemplate stringRedisTemplate(RedisConnectionFactory redisConnectionFactory) {    RedisTemplate template = new RedisTemplate<>();    template.setConnectionFactory(redisConnectionFactory);    template.setDefaultSerializer(template.getStringSerializer());    StringRedisSerializer serializer = new StringRedisSerializer();    template.setValueSerializer(serializer);    template.setHashValueSerializer(serializer);    return template;}复制代码

这他丫的原服务怎么启动的？难道RedisTemplate与StringRedisTemplate类型兼容？不会，不然我们的异常就不会报出来了。于是我切回原master分支。应用竟然启动的贼流畅。小朋友，你是不是有很多问号？我有。

问题分析

spring注入类型兼容规则是什么？

spring通过Resource注解注入类型匹配注入问题。两个注入什么样类型的数据spring会自动兼容？没错跟java的父子类型转换一样，子类型可以注入到定义为父类型的字段，但是父类型不能自动注入到定义为子类型的字段。相关源码如下：

1. 构建注入元数据含元素ResourceElement，构造器中校验类型，如果Resource注解指定了类型的情况时
2. 获取要注入到属性的bean

// 内部类：org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.ResourceElement// 该元素重写了getResourceToInject方法，即获取用来要注入到field字段的beanprotected Object getResourceToInject(Object target, String requestingBeanName) {return (this.lazyLookup ? buildLazyResourceProxy(this, requestingBeanName) :getResource(this, requestingBeanName));}// 1. 首先从jndi工厂中按照名称查找，名称优先级(Resource注解配置)：lookup->mappedName->name// 2. 其次从resourceFactory（beanFactory）中获取beanprotected Object getResource(LookupElement element, String requestingBeanName) throws BeansException {if (StringUtils.hasLength(element.mappedName)) {return this.jndiFactory.getBean(element.mappedName, element.lookupType);}if (this.alwaysUseJndiLookup) {return this.jndiFactory.getBean(element.name, element.lookupType);}if (this.resourceFactory == null) {throw new NoSuchBeanDefinitionException(element.lookupType,"No resource factory configured - specify the 'resourceFactory' property");}return autowireResource(this.resourceFactory, element, requestingBeanName);}复制代码

3. 从工厂中获取要注入的bean（即CNGetPakgOverDistanceHandler父类DwdElemeOverDistanceCheckHandler所依赖的StringRedisTemplate）（doGetBean）。TypeConverterDelegate中对类型转换并判断是否匹配通过：ClassUtils. isAssignableValue (requiredType, convertedValue)方法判断

// Check if required type matches the type of the actual bean instance.if (requiredType != null && bean != null && !requiredType.isInstance(bean)) {try {        // 如果需要的话进行类型转换：TypeConverterSupport.convertIfNecessaryreturn getTypeConverter().convertIfNecessary(bean, requiredType);}catch (TypeMismatchException ex) {if (logger.isDebugEnabled()) {logger.debug("Failed to convert bean '" + name + "' to required type '" +ClassUtils.getQualifiedName(requiredType) + "'", ex);}throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());}}复制代码

此场景下显然RedisTemplate不是StringRedisTemplate的子。抛出类型不匹配异常

为什么合并前项目可以启动成功？

打断点发现注入的StringRedisTemplate实例根本不是我们自定义配置CacheConfig中定义的bean。而是springboot自动配置中定义的StringRedisTemplate bean。 RedisAutoConfiguration配置类

@Configurationprotected static class RedisConfiguration {...@Bean@ConditionalOnMissingBean(StringRedisTemplate.class)public StringRedisTemplate stringRedisTemplate(RedisConnectionFactory redisConnectionFactory)throws UnknownHostException {StringRedisTemplate template = new StringRedisTemplate();template.setConnectionFactory(redisConnectionFactory);return template;}}复制代码

两个Configuration注解的配置类优先级是什么？

Application（springboot的source类）优先级如下（其他bean优先级相同）：

成员内部类或接口->ComponentScans->Import->ImportResource->Application自身Bean注解的方法->Application的接口->ImportResource

那么也就是说org.springframework.boot.autoconfigure.data.redis.RedisAutoConfiguration（Application的Import阶段，由SpringBootApplication注解继承的父注解EnableAutoConfiguration导入）的优先级应该是低于我们自定义CacheConfig 简单说一下EnableAutoConfigurationImportSelector的处理流程，它会从spring工厂中加载EnableAutoConfiguration的实现类进行import导入。自动配置文件根据spring-autoconfigure-metadata元数据配置进行排序、过滤，然后再执行导入。

1. Configuration配置类采集至ConfigurationClassParser.configurationClasses
2. ConfigurationClassBeanDefinitionReader遍历读取ConfigurationClassParser.configurationClasses缓存中配置类将bean定义注册至工厂

ConfigurationClassBeanDefinitionReader.loadBeanDefinitionsForConfigurationClass加载配置类中的bean定义，我们看下beanMethod方式的bean定义的处理逻辑：loadBeanDefinitionsForBeanMethod

1. 判断Conditional忽略bean定义
2. 获取bean定义的别名，读取bean注解的name属性，如果没有则默认为方法名称
3. 判断是否被已存在的bean定义重写。如果是ConfigurationClassBeanDefinition、ScannedGenericBeanDefinition、bean定义的角色大于ROLE_APPLICATION，则允许重写
4. 注册bean定义至工厂registerBeanDefinition。获取已存在的bean定义，如果不允许重写bean定义则抛出异常（默认允许）。

小结

1. 第一我们的自定义的bean优先级高于springboot自动配置的bean。
2. 第二springboot自动配置的redis bean不会生效，条件判断ConditionalOnMissingBean是注册bean阶段的条件（loadBeanDefinitionsForBeanMethod）；会直接跳过，事实也证明是如此，见下图断点已经走到（即跳过了bean注册）：

所以不论如何都应该是自定义的cacheConfig中的redis bean生效才对，也就是一定会报错

为什么合并前工厂中是springboot自动配置的redis bean？

切回master分支运行断点，依然是先走到自定义的redis bean，再走到springboot自动注册redis bean，但是竟然没有skip？那么问题的原因渐渐浮现了，问题一定是在shouldSkip条件判断这个阶段

// OnBeanCondition.getMatchOutcomeif (metadata.isAnnotated(ConditionalOnMissingBean.class.getName())) {BeanSearchSpec spec = new BeanSearchSpec(context, metadata,ConditionalOnMissingBean.class);    // 如果找到bean则返回条件不通过noMatch。查找策略为ALL，即所有List matching = getMatchingBeans(context, spec);if (!matching.isEmpty()) {return ConditionOutcome.noMatch(ConditionMessage.forCondition(ConditionalOnMissingBean.class, spec).found("bean", "beans").items(Style.QUOTE, matching));}    // 如果未找到bean则返回条件通过matchMessage = matchMessage.andCondition(ConditionalOnMissingBean.class, spec).didNotFind("any beans").atAll();}return ConditionOutcome.match(matchMessage);// 创建BeanSearchSpecBeanSearchSpec(ConditionContext context, AnnotatedTypeMetadata metadata,Class<?> annotationType) {this.annotationType = annotationType;MultiValueMap attributes = metadata.getAllAnnotationAttributes(annotationType.getName(), true);collect(attributes, "name", this.names);collect(attributes, "value", this.types);collect(attributes, "type", this.types);collect(attributes, "annotation", this.annotations);collect(attributes, "ignored", this.ignoredTypes);collect(attributes, "ignoredType", this.ignoredTypes);this.strategy = (SearchStrategy) metadata.getAnnotationAttributes(annotationType.getName()).get("search");BeanTypeDeductionException deductionException = null;try {if (this.types.isEmpty() && this.names.isEmpty()) {addDeducedBeanType(context, metadata, this.types);}}    ...}复制代码

getMatchingBeans查找bean 如果查找策略SearchStrategy是PARENTS或者ANCESTORS，则使用工厂的父类查找。 如果工厂为null则返回空集合，即ConditionalOnMissingBean条件通过 从工厂中获取所有注解type属性指定类型的beanNames（包含父子层级）。此时cacheConfig中定义的类型是RedisTemplate所以不属于指定类型。父类不能转让成子类。type=StringRedisTemplate，工厂中目前仅存在：RedisTemplate

// BeanTypeRegistrySet getNamesForType(Class<?> type) {updateTypesIfNecessary();Set matches = new LinkedHashSet();for (Map.Entry> entry : this.beanTypes.entrySet()) {if (entry.getValue() != null && type.isAssignableFrom(entry.getValue())) {matches.add(entry.getKey());}}return matches;}复制代码

从beanNames中移除条件注解ignoredTypes属性指定的类型对应的beanName 从工厂中获取所有注解annotation属性指定类型的beanNames（包含父子层级） 从工厂中获取注解name属性指定相同名称的bean（包含父子层级），调用工厂containsBean方法。没有指定name所以，最终判断条件通过继续注册bean，会覆盖自定义的cacheConfig中的redis bean

为什么合并后工厂中不是springboot自动配置的redis bean？

由于合并的分支增加了下面的配置，所以导致此处springboot的自动配置miss。

@Bean@Primarypublic StringRedisTemplate stringRedisTemplate2(RedisConnectionFactory redisConnectionFactory) {return new StringRedisTemplate(redisConnectionFactory);}复制代码

问题总结

1. 合并前，项目中没有StringRedisTemplate类型的bean，所以自动配置的bean定义会覆盖掉自定义bean定义。所以自定义的bean定义是错的也没有抛出异常
2. 合并后，项目中存在StringRedisTemplate类型的bean配置，所以自动配置的bean定义不会覆盖掉自定义bean定义。注入时根据名称匹配注入，因为自定义的配置类型是错误的RedisTemplate类型。于是抛出了异常