Mybatis源码解析

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sqlSessionTemplateRefString 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sqlSessionFactoryBeanNameString 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 ClassPathMapperScannerscanner.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 MapperFactoryBeandefinition.setBeanClass(this.mapperFactoryBeanClass);// 给 MapperFactoryBean 添加属性字段 addToConfigdefinition.getPropertyValues().add("addToConfig", this.addToConfig);boolean explicitFactoryUsed = false;// 给 MapperFactoryBean 添加属性字段 sqlSessionFactoryif (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 sqlSessionTemplateif (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);}}
}