许久没有写springboot，为测试某个功能，手动写了个简单的demo,记录一个简单但常见的小问题。
报错：
** WARNING ** : Your ApplicationContext is unlikely to start due to a @ComponentScan of the default package.
2020-11-11 09:44:49.704 WARN 3844 --- [ main] ationConfigEmbeddedWebApplicationContext : Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.BeanDefinitionStoreException: Failed to read candidate component class: URL [jar:file:/C:/Users/19821/.m2/repository/org/springframework/boot/spring-boot-autoconfigure/1.5.8.RELEASE/spring-boot-autoconfigure-1.5.8.RELEASE.jar!/org/springframework/boot/autoconfigure/jdbc/DataSourceAutoConfiguration$EmbeddedDatabaseConfiguration.class]; nested exception is java.lang.IllegalStateException: Could not evaluate condition on org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration$EmbeddedDatabaseConfiguration due to org/springframework/dao/DataAccessException not found. Make sure your own configuration does not rely on that class. This can also happen if you are @ComponentScanning a springframework package (e.g. if you put a @ComponentScan in the default package by mistake)
2020-11-11 09:44:49.708 ERROR 3844 --- [ main] o.s.b.f.s.DefaultListableBeanFactory : Destroy method on bean with name 'org.springframework.boot.autoconfigure.internalCachingMetadataReaderFactory' threw an exception
java.lang.IllegalStateException: ApplicationEventMulticaster not initialized - call 'refresh' before multicasting events via the context: org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext@f4168b8: startup date [Wed Nov 11 09:44:41 CST 2020]; root of context hierarchy
at org.springframework.context.support.AbstractApplicationContext.getApplicationEventMulticaster(AbstractApplicationContext.java:414) [spring-context-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.context.support.ApplicationListenerDetector.postProcessBeforeDestruction(ApplicationListenerDetector.java:97) ~[spring-context-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.beans.factory.support.DisposableBeanAdapter.destroy(DisposableBeanAdapter.java:253) ~[spring-beans-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.destroyBean(DefaultSingletonBeanRegistry.java:578) [spring-beans-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.destroySingleton(DefaultSingletonBeanRegistry.java:554) [spring-beans-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.beans.factory.support.DefaultListableBeanFactory.destroySingleton(DefaultListableBeanFactory.java:961) [spring-beans-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.destroySingletons(DefaultSingletonBeanRegistry.java:523) [spring-beans-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.beans.factory.support.FactoryBeanRegistrySupport.destroySingletons(FactoryBeanRegistrySupport.java:230) [spring-beans-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.beans.factory.support.DefaultListableBeanFactory.destroySingletons(DefaultListableBeanFactory.java:968) [spring-beans-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.context.support.AbstractApplicationContext.destroyBeans(AbstractApplicationContext.java:1030) [spring-context-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:556) [spring-context-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.refresh(EmbeddedWebApplicationContext.java:122) [spring-boot-1.5.8.RELEASE.jar:1.5.8.RELEASE]
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:693) [spring-boot-1.5.8.RELEASE.jar:1.5.8.RELEASE]
at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:360) [spring-boot-1.5.8.RELEASE.jar:1.5.8.RELEASE]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:303) [spring-boot-1.5.8.RELEASE.jar:1.5.8.RELEASE]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1118) [spring-boot-1.5.8.RELEASE.jar:1.5.8.RELEASE]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1107) [spring-boot-1.5.8.RELEASE.jar:1.5.8.RELEASE]
at MainApplication.main(MainApplication.java:8) [classes/:na]
2020-11-11 09:44:49.712 INFO 3844 --- [ main] utoConfigurationReportLoggingInitializer :
Error starting ApplicationContext. To display the auto-configuration report re-run your application with 'debug' enabled.
2020-11-11 09:44:49.718 ERROR 3844 --- [ main] o.s.boot.SpringApplication : Application startup failed
org.springframework.beans.factory.BeanDefinitionStoreException: Failed to read candidate component class: URL [jar:file:/C:/Users/19821/.m2/repository/org/springframework/boot/spring-boot-autoconfigure/1.5.8.RELEASE/spring-boot-autoconfigure-1.5.8.RELEASE.jar!/org/springframework/boot/autoconfigure/jdbc/DataSourceAutoConfiguration$EmbeddedDatabaseConfiguration.class]; nested exception is java.lang.IllegalStateException: Could not evaluate condition on org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration$EmbeddedDatabaseConfiguration due to org/springframework/dao/DataAccessException not found. Make sure your own configuration does not rely on that class. This can also happen if you are @ComponentScanning a springframework package (e.g. if you put a @ComponentScan in the default package by mistake)
at org.springframework.context.annotation.ClassPathScanningCandidateComponentProvider.findCandidateComponents(ClassPathScanningCandidateComponentProvider.java:311) ~[spring-context-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.context.annotation.ClassPathBeanDefinitionScanner.doScan(ClassPathBeanDefinitionScanner.java:272) ~[spring-context-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.context.annotation.ComponentScanAnnotationParser.parse(ComponentScanAnnotationParser.java:135) ~[spring-context-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.context.annotation.ConfigurationClassParser.doProcessConfigurationClass(ConfigurationClassParser.java:287) ~[spring-context-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.context.annotation.ConfigurationClassParser.processConfigurationClass(ConfigurationClassParser.java:245) ~[spring-context-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.context.annotation.ConfigurationClassParser.parse(ConfigurationClassParser.java:198) ~[spring-context-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.context.annotation.ConfigurationClassParser.parse(ConfigurationClassParser.java:167) ~[spring-context-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.context.annotation.ConfigurationClassPostProcessor.processConfigBeanDefinitions(ConfigurationClassPostProcessor.java:308) ~[spring-context-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.context.annotation.ConfigurationClassPostProcessor.postProcessBeanDefinitionRegistry(ConfigurationClassPostProcessor.java:228) ~[spring-context-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanDefinitionRegistryPostProcessors(PostProcessorRegistrationDelegate.java:272) ~[spring-context-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(PostProcessorRegistrationDelegate.java:92) ~[spring-context-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.context.support.AbstractApplicationContext.invokeBeanFactoryPostProcessors(AbstractApplicationContext.java:687) ~[spring-context-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:525) ~[spring-context-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.refresh(EmbeddedWebApplicationContext.java:122) ~[spring-boot-1.5.8.RELEASE.jar:1.5.8.RELEASE]
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:693) [spring-boot-1.5.8.RELEASE.jar:1.5.8.RELEASE]
at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:360) [spring-boot-1.5.8.RELEASE.jar:1.5.8.RELEASE]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:303) [spring-boot-1.5.8.RELEASE.jar:1.5.8.RELEASE]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1118) [spring-boot-1.5.8.RELEASE.jar:1.5.8.RELEASE]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1107) [spring-boot-1.5.8.RELEASE.jar:1.5.8.RELEASE]
at MainApplication.main(MainApplication.java:8) [classes/:na]
Caused by: java.lang.IllegalStateException: Could not evaluate condition on org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration$EmbeddedDatabaseConfiguration due to org/springframework/dao/DataAccessException not found. Make sure your own configuration does not rely on that class. This can also happen if you are @ComponentScanning a springframework package (e.g. if you put a @ComponentScan in the default package by mistake)
at org.springframework.boot.autoconfigure.condition.SpringBootCondition.matches(SpringBootCondition.java:55) ~[spring-boot-autoconfigure-1.5.8.RELEASE.jar:1.5.8.RELEASE]
at org.springframework.context.annotation.ConditionEvaluator.shouldSkip(ConditionEvaluator.java:102) ~[spring-context-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.context.annotation.ConditionEvaluator.shouldSkip(ConditionEvaluator.java:81) ~[spring-context-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.context.annotation.ConditionEvaluator.shouldSkip(ConditionEvaluator.java:64) ~[spring-context-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.context.annotation.ClassPathScanningCandidateComponentProvider.isConditionMatch(ClassPathScanningCandidateComponentProvider.java:371) ~[spring-context-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.context.annotation.ClassPathScanningCandidateComponentProvider.isCandidateComponent(ClassPathScanningCandidateComponentProvider.java:355) ~[spring-context-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.context.annotation.ClassPathScanningCandidateComponentProvider.findCandidateComponents(ClassPathScanningCandidateComponentProvider.java:288) ~[spring-context-4.3.12.RELEASE.jar:4.3.12.RELEASE]
... 19 common frames omitted
Caused by: java.lang.NoClassDefFoundError: org/springframework/dao/DataAccessException
at org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration$EmbeddedDatabaseCondition.getMatchOutcome(DataSourceAutoConfiguration.java:211) ~[spring-boot-autoconfigure-1.5.8.RELEASE.jar:1.5.8.RELEASE]
at org.springframework.boot.autoconfigure.condition.SpringBootCondition.matches(SpringBootCondition.java:47) ~[spring-boot-autoconfigure-1.5.8.RELEASE.jar:1.5.8.RELEASE]
... 25 common frames omitted
Caused by: java.lang.ClassNotFoundException: org.springframework.dao.DataAccessException
at java.net.URLClassLoader.findClass(URLClassLoader.java:381) ~[na:1.8.0_172]
at java.lang.ClassLoader.loadClass(ClassLoader.java:424) ~[na:1.8.0_172]
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:349) ~[na:1.8.0_172]
at java.lang.ClassLoader.loadClass(ClassLoader.java:357) ~[na:1.8.0_172]
... 27 common frames omitted
Process finished with exit code 1根据上述报错内容，第一反应应该是缺少jar包， 但实际上并不是，这个是Application类的存放位置问题。
之前位置图:
移动到正确位置：
放到自己创建的package下后重新运行就正常了，不能直接放在默认的java目录下，不然无法扫描识别到。
PS:在pom中创建好依赖后代码中使用某些注解无效，这是因为引入的jar包还没加载进项目，把MAVEN进行Reimport下就行。