Mybatis执行sql流程(二)之加载Mapper

Mybatis加载Mapper

注册方式	注册时机	特点
`@MapperScan`	Bean定义阶段注册接口定义	批量注册，推荐方式
`@Mapper` (接口注解)	同 `@MapperScan`	需每个接口单独标注
XML 配置 `<mapper>`	MyBatis 初始化时	传统方式，不依赖 Spring 容器
`SqlSessionTemplate` 直接获取	调用时	编程式获取，不自动注册为 Bean

@MapperScan注册mapper

// 使用：在启动类上添加注解
@MapperScan("com.zy.**.mapper")

@Import(MapperScannerRegistrar.class) // 此处使用了@Import注解，用于导入其他配置
@Repeatable(MapperScans.class)
public @interface MapperScan {...;
}

/**
1.指示要导入的一个或多个组件，通常是@Configuration类。
2.提供与Spring XML中的<import/>元素等效的功能。
3.允许导入@Configuration类，ImportSelector和ImportBeanDefinitionRegistrar实现，以及常规组件类（从4.2开始，类似于AnnotationConfigApplicationContext.register）。
4.导入的@Configuration类中声明的@Bean定义应该使用@Autowired注入来访问。也可以自动连接声明bean的配置类实例。
5.如果需要导入XML或其他非@Configuration bean定义资源，请改用@ImportResource注解。
*/public @interface Import {/*** {@link Configuration @Configuration}, {@link ImportSelector},* {@link ImportBeanDefinitionRegistrar}, or regular component classes to import.*/Class<?>[] value();}

// 实现了ImportBeanDefinitionRegistrar接口，此处涉及到Spring加载BeanDefinition的逻辑
public class MapperScannerRegistrar implements ImportBeanDefinitionRegistrar, ResourceLoaderAware {private ResourceLoader resourceLoader;// 重写ImportBeanDefinitionRegistrar 接口中的registerBeanDefinitions 方法@Overridepublic void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {// 1. 获取@MapperScan注解属性AnnotationAttributes mapperScanAttrs = AnnotationAttributes.fromMap(importingClassMetadata.getAnnotationAttributes(MapperScan.class.getName()));// 2. 实际注册逻辑if (mapperScanAttrs != null) {registerBeanDefinitions(importingClassMetadata, mapperScanAttrs, registry,generateBaseBeanName(importingClassMetadata, 0));}}/**annoMeta 被注解类的元数据annoAttrs @MapperScan 注解的属性值registry : Spring bean 定义注册器beanName ：要注册的 Bean 名称*/void registerBeanDefinitions(AnnotationMetadata annoMeta, AnnotationAttributes annoAttrs,BeanDefinitionRegistry registry, String beanName) {
// 创建MapperScannerConfigurer 的通用Bean定义构建器。此处还只是构造builder。BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition(MapperScannerConfigurer.class);// 启用属性占位符处理（如 ${jdbc.url}）builder.addPropertyValue("processPropertyPlaceHolders", true);// 注解类过滤：如果设置了annotationClass（如@Mapper），则只扫描带该注解的接口Class<? extends Annotation> annotationClass = annoAttrs.getClass("annotationClass");if (!Annotation.class.equals(annotationClass)) {builder.addPropertyValue("annotationClass", annotationClass);}
// 标记接口过滤：如果设置了 markerInterface， 则只扫描实现该接口的MapperClass<?> markerInterface = annoAttrs.getClass("markerInterface");if (!Class.class.equals(markerInterface)) {builder.addPropertyValue("markerInterface", markerInterface);}
// Bean 名称生成器Class<? extends BeanNameGenerator> generatorClass = annoAttrs.getClass("nameGenerator");if (!BeanNameGenerator.class.equals(generatorClass)) {builder.addPropertyValue("nameGenerator", BeanUtils.instantiateClass(generatorClass));}
// 工厂类覆盖Class<? extends MapperFactoryBean> mapperFactoryBeanClass = annoAttrs.getClass("factoryBean");if (!MapperFactoryBean.class.equals(mapperFactoryBeanClass)) {builder.addPropertyValue("mapperFactoryBeanClass", mapperFactoryBeanClass);}
// SQL 会话模板引用：支持指定特定的 SqlSessionTemplate BeanString sqlSessionTemplateRef = annoAttrs.getString("sqlSessionTemplateRef");if (StringUtils.hasText(sqlSessionTemplateRef)) {builder.addPropertyValue("sqlSessionTemplateBeanName", annoAttrs.getString("sqlSessionTemplateRef"));}
// SQL 会话工厂引用String sqlSessionFactoryRef = annoAttrs.getString("sqlSessionFactoryRef");if (StringUtils.hasText(sqlSessionFactoryRef)) {builder.addPropertyValue("sqlSessionFactoryBeanName", annoAttrs.getString("sqlSessionFactoryRef"));}List<String> basePackages = new ArrayList<>();// 添加 value 属性值（包路径）basePackages.addAll(Arrays.stream(annoAttrs.getStringArray("value")).filter(StringUtils::hasText).collect(Collectors.toList()));
// 添加 basePackages 属性值basePackages.addAll(Arrays.stream(annoAttrs.getStringArray("basePackages")).filter(StringUtils::hasText).collect(Collectors.toList()));
// 添加basePackageClasses的包路径basePackages.addAll(Arrays.stream(annoAttrs.getClassArray("basePackageClasses")).map(ClassUtils::getPackageName).collect(Collectors.toList()));
// 使用默认配置类所在包if (basePackages.isEmpty()) {basePackages.add(getDefaultBasePackage(annoMeta));}
// 延迟初始化String lazyInitialization = annoAttrs.getString("lazyInitialization");if (StringUtils.hasText(lazyInitialization)) {builder.addPropertyValue("lazyInitialization", lazyInitialization);}
// Bean 作用域String defaultScope = annoAttrs.getString("defaultScope");if (!AbstractBeanDefinition.SCOPE_DEFAULT.equals(defaultScope)) {builder.addPropertyValue("defaultScope", defaultScope);}
// 设置扫描包路径（逗号分割）builder.addPropertyValue("basePackage", StringUtils.collectionToCommaDelimitedString(basePackages));// for spring-nativebuilder.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
// 注册Bean 定义。上述都是在配置builder， 此处才开始注册bean definitionregistry.registerBeanDefinition(beanName, builder.getBeanDefinition());}
}

MapperScannerConfigurer 作为BeanDefinitionRegistryPostProcessor执行，中重写了 postProcessBeanDefinitionRegistry 方法，最终调用doScan(basePackages);扫描Mapper

public class ClassPathMapperScanner extends ClassPathBeanDefinitionScanner {@Overridepublic Set<BeanDefinitionHolder> doScan(String... basePackages) {// 1. 调用父类扫描方法获取Bean定义Set<BeanDefinitionHolder> beanDefinitions = super.doScan(basePackages);if (beanDefinitions.isEmpty()) {logger.warn("No MyBatis mapper was found...");} else {// 2. 处理扫描到的Bean定义processBeanDefinitions(beanDefinitions);}return beanDefinitions;}
// 省略部分代码private void processBeanDefinitions(Set<BeanDefinitionHolder> beanDefinitions) {for (BeanDefinitionHolder holder : beanDefinitions) {GenericBeanDefinition definition = (GenericBeanDefinition) holder.getBeanDefinition();// 3. 获取Mapper接口名String mapperClassName = definition.getBeanClassName();// 4. BeanClass 转换为 MapperFactoryBean// 关键步骤1：添加构造参数（原始Mapper接口）definition.getConstructorArgumentValues().addGenericArgumentValue(mapperClassName);try {// 关键步骤2：设置 MapperInterface 属性（Spring Native 兼容）definition.getPropertyValues().add("mapperInterface", Resources.classForName(beanClassName));} catch (ClassNotFoundException ignore) {// ignore}// 关键步骤3：替换 Bean 类为 MapperFactoryBeandefinition.setBeanClass(this.mapperFactoryBeanClass);// 省略部分SqlSessionFactory 、sqlSessionTemplate相关内容。优先级：SqlSessionTemplate > SqlSessionFactory// 5. 设置自动装配模式：当未显示配置工厂/模板时，启用按类型自动装配if (!explicitFactoryUsed) {LOGGER.debug("Enabling autowire by type...");definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE);}}}
}

转换前Bean定义：

BeanDefinition {beanClass = com.example.UserMapper // 原始接口scope = singleton...
}

转换后 Bean 定义

BeanDefinition {beanClass = MapperFactoryBean // 替换为工厂类constructorArgs = [com.example.UserMapper] // 原始接口作为构造参数properties = {sqlSessionFactory = ref("sqlSessionFactory") // 自动装配addToConfig = true}...
}

实际效果：

// 用户代码
@Autowired
UserMapper userMapper; // 实际发生
MapperFactoryBean factoryBean = new MapperFactoryBean(UserMapper.class);
factoryBean.setSqlSessionFactory(sqlSessionFactory);
UserMapper proxy = factoryBean.getObject(); // 返回 MyBatis 代理

// MapperFactoryBean 的 getObject() 
@Overridepublic T getObject() throws Exception {return getSqlSession().getMapper(this.mapperInterface); // 此处就是获取的代理类对象 }

// 从 @Autowired 到factoryBean.getObject(); 的过程：
@Autowired-> AutowiredAnnotationBeanPostProcessor.postProcessProperties()-> InjectionMetadata.inject()-> DefaultListableBeanFactory.doGetBean()-> AbstractBeanFactory.getObjectForBeanInstance(),发现 MapperFacoryBean 是 UserMapper 类型的工厂-> AbstractBeanFactory..getObjectFromFactoryBean()-> FactoryBeanRegistrySupport.doGetObjectFromFactoryBean()-> FactoryBean<?>.getObject()