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一、问题描述

最近在使用MybatisPlus时遇到了一个小问题，这是项目结构：

刚开始在SpringBootApplication中添加了扫描的mapper类位置：

@SpringBootApplication
@MapperScan("com.example.mybatisplusdemo.mapper")
public class MybatisPlusDemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(MybatisPlusDemoApplication.class, args);
    }
}

后面在使用MybatisPlus的分页插件新建了一个MybatisPlus的插件管理类MybatisPlusConfig，为了统一管理管理mybatis的配置，将@MapperScan在该类中配置，并删除SpringBootApplication类中的@MapperScan，如下：

@Configuration
@MapperScan("com.example.mybatisplusdemo.mapper")
public class MybatisPlusConfig {
    @Bean
    public MybatisPlusInterceptor mybatisPlusInterceptor(){
        MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();
        interceptor.addInnerInterceptor(new PaginationInnerInterceptor(DbType.MYSQL));
        return interceptor;
    }
}

但是后面对分页插件测试的时候报错：

Caused by: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'userServiceImpl': Unsatisfied dependency expressed through field 'baseMapper'; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'com.example.mybatisplusdemo.mapper.UserMapper' 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$AutowiredFieldElement.resolveFieldValue(AutowiredAnnotationBeanPostProcessor.java:659) ~[spring-beans-5.3.18.jar:5.3.18]
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:639) ~[spring-beans-5.3.18.jar:5.3.18]
	at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:119) ~[spring-beans-5.3.18.jar:5.3.18]
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessProperties(AutowiredAnnotationBeanPostProcessor.java:399) ~[spring-beans-5.3.18.jar:5.3.18]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1431) ~[spring-beans-5.3.18.jar:5.3.18]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:619) ~[spring-beans-5.3.18.jar:5.3.18]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:542) ~[spring-beans-5.3.18.jar:5.3.18]
	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:335) ~[spring-beans-5.3.18.jar:5.3.18]
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234) ~[spring-beans-5.3.18.jar:5.3.18]
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:333) ~[spring-beans-5.3.18.jar:5.3.18]
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:208) ~[spring-beans-5.3.18.jar:5.3.18]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:953) ~[spring-beans-5.3.18.jar:5.3.18]
	at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:918) ~[spring-context-5.3.18.jar:5.3.18]
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:583) ~[spring-context-5.3.18.jar:5.3.18]
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:740) ~[spring-boot-2.6.6.jar:2.6.6]
	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:415) ~[spring-boot-2.6.6.jar:2.6.6]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:303) ~[spring-boot-2.6.6.jar:2.6.6]
	at org.springframework.boot.test.context.SpringBootContextLoader.loadContext(SpringBootContextLoader.java:136) ~[spring-boot-test-2.6.6.jar:2.6.6]
	at org.springframework.test.context.cache.DefaultCacheAwareContextLoaderDelegate.loadContextInternal(DefaultCacheAwareContextLoaderDelegate.java:99) ~[spring-test-5.3.18.jar:5.3.18]
	at org.springframework.test.context.cache.DefaultCacheAwareContextLoaderDelegate.loadContext(DefaultCacheAwareContextLoaderDelegate.java:124) ~[spring-test-5.3.18.jar:5.3.18]
	... 72 common frames omitted
Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'com.example.mybatisplusdemo.mapper.UserMapper' 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:1799) ~[spring-beans-5.3.18.jar:5.3.18]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1355) ~[spring-beans-5.3.18.jar:5.3.18]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1309) ~[spring-beans-5.3.18.jar:5.3.18]
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.resolveFieldValue(AutowiredAnnotationBeanPostProcessor.java:656) ~[spring-beans-5.3.18.jar:5.3.18]
	... 91 common frames omitted

二、解决思路

1.保持SpringBoot启动类的@MapperScan

保持SpringBoot启动类上的@MapperScan不变，无需在其他配置文件类中使用@MappaerScan。

2.在*.mapper接口上加上@mapper

如果非要在其他配置类中使用@MapperScan来替换启动类上的@MapperScan的话，那么需要在所有的Mapper接口上使用@Mapper注解（感觉更麻烦了），如下：

@Component
@Mapper
public interface UserMapper extends BaseMapper<User> {
    User selectAllByName(String userName);
}

目前还不知道为什么出现该问题的原因，应该是在配置类中使用@MapperScan的时候如果不使用@Mapper直接标记Mapper接口的话，就无法扫描到，希望大家在评论区给出自己的见解。