Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException

1. 报错信息

Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'com.yang.mapper.EmployeeMapper' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.raiseNoMatchingBeanFound(DefaultListableBeanFactory.java:1801) ~[spring-beans-5.3.30.jar:5.3.30]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1357) ~[spring-beans-5.3.30.jar:5.3.30]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1311) ~[spring-beans-5.3.30.jar:5.3.30]
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.resolveFieldValue(AutowiredAnnotationBeanPostProcessor.java:710) ~[spring-beans-5.3.30.jar:5.3.30]
	... 41 common frames omitted

2. 完整错误信息

Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
2023-09-26 22:23:21.560 ERROR 21128 --- [  restartedMain] o.s.boot.SpringApplication               : Application run failed

org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'employeeController': Unsatisfied dependency expressed through field 'employeeService'; nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'employeeServiceImpl': Unsatisfied dependency expressed through field 'baseMapper'; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'com.yang.mapper.EmployeeMapper' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.resolveFieldValue(AutowiredAnnotationBeanPostProcessor.java:713) ~[spring-beans-5.3.30.jar:5.3.30]
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:693) ~[spring-beans-5.3.30.jar:5.3.30]
	at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:119) ~[spring-beans-5.3.30.jar:5.3.30]
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessProperties(AutowiredAnnotationBeanPostProcessor.java:408) ~[spring-beans-5.3.30.jar:5.3.30]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1431) ~[spring-beans-5.3.30.jar:5.3.30]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:619) ~[spring-beans-5.3.30.jar:5.3.30]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:542) ~[spring-beans-5.3.30.jar:5.3.30]
	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:335) ~[spring-beans-5.3.30.jar:5.3.30]
	at org.springframework.beans.factory.support.AbstractBeanFactory$$Lambda$226/1096477616.getObject(Unknown Source) ~[na:na]
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234) ~[spring-beans-5.3.30.jar:5.3.30]
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:333) ~[spring-beans-5.3.30.jar:5.3.30]
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:208) ~[spring-beans-5.3.30.jar:5.3.30]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:955) ~[spring-beans-5.3.30.jar:5.3.30]
	at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:921) ~[spring-context-5.3.30.jar:5.3.30]
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:583) ~[spring-context-5.3.30.jar:5.3.30]
	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:147) ~[spring-boot-2.7.16.jar:2.7.16]
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:731) [spring-boot-2.7.16.jar:2.7.16]
	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:408) [spring-boot-2.7.16.jar:2.7.16]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:307) [spring-boot-2.7.16.jar:2.7.16]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1303) [spring-boot-2.7.16.jar:2.7.16]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1292) [spring-boot-2.7.16.jar:2.7.16]
	at com.yang.ReggieProjectApplication.main(ReggieProjectApplication.java:19) [classes/:na]
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_40]
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_40]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_40]
	at java.lang.reflect.Method.invoke(Method.java:497) ~[na:1.8.0_40]
	at org.springframework.boot.devtools.restart.RestartLauncher.run(RestartLauncher.java:50) [spring-boot-devtools-2.7.16.jar:2.7.16]
Caused by: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'employeeServiceImpl': Unsatisfied dependency expressed through field 'baseMapper'; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'com.yang.mapper.EmployeeMapper' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.resolveFieldValue(AutowiredAnnotationBeanPostProcessor.java:713) ~[spring-beans-5.3.30.jar:5.3.30]
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:693) ~[spring-beans-5.3.30.jar:5.3.30]
	at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:119) ~[spring-beans-5.3.30.jar:5.3.30]
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessProperties(AutowiredAnnotationBeanPostProcessor.java:408) ~[spring-beans-5.3.30.jar:5.3.30]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1431) ~[spring-beans-5.3.30.jar:5.3.30]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:619) ~[spring-beans-5.3.30.jar:5.3.30]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:542) ~[spring-beans-5.3.30.jar:5.3.30]
	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:335) ~[spring-beans-5.3.30.jar:5.3.30]
	at org.springframework.beans.factory.support.AbstractBeanFactory$$Lambda$226/1096477616.getObject(Unknown Source) ~[na:na]
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234) ~[spring-beans-5.3.30.jar:5.3.30]
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:333) ~[spring-beans-5.3.30.jar:5.3.30]
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:208) ~[spring-beans-5.3.30.jar:5.3.30]
	at org.springframework.beans.factory.config.DependencyDescriptor.resolveCandidate(DependencyDescriptor.java:276) ~[spring-beans-5.3.30.jar:5.3.30]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1391) ~[spring-beans-5.3.30.jar:5.3.30]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1311) ~[spring-beans-5.3.30.jar:5.3.30]
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.resolveFieldValue(AutowiredAnnotationBeanPostProcessor.java:710) ~[spring-beans-5.3.30.jar:5.3.30]
	... 26 common frames omitted
Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'com.yang.mapper.EmployeeMapper' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.raiseNoMatchingBeanFound(DefaultListableBeanFactory.java:1801) ~[spring-beans-5.3.30.jar:5.3.30]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1357) ~[spring-beans-5.3.30.jar:5.3.30]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1311) ~[spring-beans-5.3.30.jar:5.3.30]
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.resolveFieldValue(AutowiredAnnotationBeanPostProcessor.java:710) ~[spring-beans-5.3.30.jar:5.3.30]
	... 41 common frames omitted

3. 解决方法

首先我们还是需要从下往上看找到第一个出现Caused by的地方认真研读，解决了这个问题你的整个问题就应该解决了 .从错误提示中我们可以看出是mapper包下出现了错误。以下是我的代码结构，可以看出是在EmployeeMapper下出现了问题

通过查看EmployeeMapper

可以发现我们使用了@Repository注解，但是在启动类下，没有使用@MapperScan进行扫描，所以并没有将这个mapper交给Spring来管理 所以我们需要在启动类下添加@MapperScan(“mapper包的全类名”)，此时在启动项目，或者另一种简单的办法就是直接在mapper类上使用@Mapper注解。
然后重启项目，就可以运行了。

以此来扩展以下@Mapper和@Repository的区别

1.相同点
@Mapper和@Repository都是作用在dao层接口，使得其生成代理对象bean，交给spring 容器管理，对于mybatis来说，都可以不用写mapper.xml文件

2.不同点
@Repository需要在Spring中配置扫描地址，然后生成Dao层的Bean才能被注入到Service层中
@Mapper不需要配置扫描地址，通过xml里面的namespace里面的接口地址，生成了Bean后注入到Service层中
也就是@Repository多了一个配置扫描地址的步骤。（需要在启动类上添加@MapperScan(“具体的mapper所在的包名”） e.g@MapperScan(“com.yang.mapper”)