MybatisAutoConfiguration或者MybatisPlusAutoConfiguration核心作用是初始化工厂类SqlSessionFactory，其中包含属性interceptors、MapperLocations、TypeAliasesPackage、TypeEnumsPackage、TypeHandlers等。

MybatisAutoConfiguration自动装配类是由依赖：mybatis-spring-boot-starter【mybatis-spring-boot-autoconfigure】提供的，如果使用Mp版本则直接由MybatisPlusAutoConfiguration替代MybatisAutoConfiguration。

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@Mapper通过@Import注解导入ImportBeanDefinitionRegistrar类型的实现类MapperScannerRegistrar，类ImportBeanDefinitionRegistrar的作用：

1. 核心是引入类MapperScannerConfigurer，即初始化其对应的BeanDefinition，并注册至IOC中BeanDefinition类型的注册表中。
2. MapperScannerConfigurer实为BeanDefinitionRegistryPostProcessor类型的后置处理器。
3. 注解@MapperScan相关属性value重置到MapperScannerConfigurer对应的BeanDefinition内部。
4. 将MapperScannerConfigurer对应的BeanDefinition注册至Spring IOC容器内部。

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BeanDefinitionRegistryPostProcessor类型的后置处理器MapperScannerConfigurer：此时@Mapper注解相关属性重置于MapperScannerConfigurer。

1. 扫描basePackages路径下全部的Mapper接口。
2. 遍历每一个接口为其生成BeanDefinition，其内部beanClass属性value为MapperFactoryBean。
3. 将@Mapper组合注解相关属性转化为MapperFactoryBean相关字段或者方法属性。

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@Mapper -> MapperScannerRegistrar -> MapperScannerConfigurer-> MapperFactoryBean转化流程：

public class MapperScannerRegistrar implements ImportBeanDefinitionRegistrar{
    public void registerBeanDefinitions(AnnotationAttributes annoAttrs,BeanDefinitionRegistry registry, String beanName) {
        BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition(MapperScannerConfigurer.class);
        ...
        // 将 @MapperScan 属性sqlSessionTemplateRef 作为 MapperScannerConfigurer的属性sqlSessionTemplateRef
        String sqlSessionTemplateRef = annoAttrs.getString("sqlSessionTemplateRef");
        if (StringUtils.hasText(sqlSessionTemplateRef)) {
            builder.addPropertyValue("sqlSessionTemplateBeanName",annoAttrs.getString("sqlSessionTemplateRef"));
        }
        // 将 @MapperScan 属性sqlSessionFactoryRef 作为 MapperScannerConfigurer的属性sqlSessionFactoryBeanName
        String sqlSessionFactoryRef = annoAttrs.getString("sqlSessionFactoryRef");
        if (StringUtils.hasText(sqlSessionFactoryRef)) {
          builder.addPropertyValue("sqlSessionFactoryBeanName",annoAttrs.getString("sqlSessionFactoryRef"));
        }
        ...
        registry.registerBeanDefinition(beanName, builder.getBeanDefinition());
    }
}

以上将注解@MapperScan 属性转移到MapperScannerConfigurer。

public class MapperScannerConfigurer implements BeanDefinitionRegistryPostProcessor, InitializingBean{
    private boolean addToConfig = true;
    private SqlSessionFactory sqlSessionFactory;
    private SqlSessionTemplate sqlSessionTemplate;
    private String sqlSessionFactoryBeanName;
    private String sqlSessionTemplateBeanName;

    public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {
        ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry);
        //以下将 @MapperScan 相关属性转移到 ClassPathMapperScanner
        scanner.setAddToConfig(this.addToConfig);
        scanner.setAnnotationClass(this.annotationClass);
        scanner.setMarkerInterface(this.markerInterface);
        scanner.setSqlSessionFactory(this.sqlSessionFactory);
        scanner.setSqlSessionTemplate(this.sqlSessionTemplate);
        scanner.setSqlSessionFactoryBeanName(this.sqlSessionFactoryBeanName);
        scanner.setSqlSessionTemplateBeanName(this.sqlSessionTemplateBeanName);
        scanner.setResourceLoader(this.applicationContext);
        scanner.setBeanNameGenerator(this.nameGenerator);
        scanner.setMapperFactoryBeanClass(this.mapperFactoryBeanClass);
        scanner.registerFilters();
        scanner.scan(StringUtils.tokenizeToStringArray(this.basePackage,",; \t\n"));
    }
}

 将 MapperScannerConfigurer 相关属性转移到类ClassPathMapperScanner。

public class ClassPathMapperScanner extends ClassPathBeanDefinitionScanner {
  
    private Class<? extends MapperFactoryBean> mapperFactoryBeanClass = MapperFactoryBean.class;

    private void processBeanDefinitions(Set<BeanDefinitionHolder> beanDefinitions) {
        GenericBeanDefinition definition;
        for (BeanDefinitionHolder holder : beanDefinitions) {//basePackages路径下扫描得到全部Mapper接口
            ...
            // 将 Mapper接口之 GenericBeanDefinition 的BeanClass属性为 MapperFactoryBean
            definition.setBeanClass(this.mapperFactoryBeanClass);
            // 给 MapperFactoryBean 添加属性字段 addToConfig
            definition.getPropertyValues().add("addToConfig", this.addToConfig);

            boolean explicitFactoryUsed = false;
            // 给 MapperFactoryBean 添加属性字段 sqlSessionFactory
            if (StringUtils.hasText(this.sqlSessionFactoryBeanName)) {
                definition.getPropertyValues().add("sqlSessionFactory",new RuntimeBeanReference(this.sqlSessionFactoryBeanName));
                explicitFactoryUsed = true;
            } else if (this.sqlSessionFactory != null) {
                definition.getPropertyValues().add("sqlSessionFactory", this.sqlSessionFactory);
                explicitFactoryUsed = true;
            }
            // 给 MapperFactoryBean 添加属性字段 sqlSessionTemplate
            if (StringUtils.hasText(this.sqlSessionTemplateBeanName)) {
                definition.getPropertyValues().add("sqlSessionTemplate",new RuntimeBeanReference(this.sqlSessionTemplateBeanName));
                explicitFactoryUsed = true;
            } else if (this.sqlSessionTemplate != null) {
                definition.getPropertyValues().add("sqlSessionTemplate", this.sqlSessionTemplate);
                explicitFactoryUsed = true;
            }
              definition.setLazyInit(lazyInitialization);
      }
    }
}