深入探究Java @MapperScan实现原理

@MapperScan("com.xxx.mapper")

public interface ImportBeanDefinitionRegistrar {
	/**
	 * 注册自定义BeanDefinition
	 *
	 * @param importingClassMetadata 导入类的元数据，被谁导入的
	 * @param registry BeanDefinition注册器
	 */
	void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry);
}

public class MapperScannerRegistrar implements ImportBeanDefinitionRegistrar, ResourceLoaderAware {
  private ResourceLoader resourceLoader;
  @Override
  public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
  	// 注解属性
    AnnotationAttributes annoAttrs = AnnotationAttributes.fromMap(importingClassMetadata.getAnnotationAttributes(MapperScan.class.getName()));
    // 创建自定义的Mapper扫描器，用来扫描Mapper接口
    ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry);
    // this check is needed in Spring 3.1
    if (resourceLoader != null) {
      scanner.setResourceLoader(resourceLoader);
    }
    Class<? extends Annotation> annotationClass = annoAttrs.getClass("annotationClass");
    if (!Annotation.class.equals(annotationClass)) {
      // 如果指定了注解，则只扫描加了指定注解的Mapper接口
      scanner.setAnnotationClass(annotationClass);
    }
    Class<?> markerInterface = annoAttrs.getClass("markerInterface");
    if (!Class.class.equals(markerInterface)) {
      scanner.setMarkerInterface(markerInterface);
    }
    Class<? extends BeanNameGenerator> generatorClass = annoAttrs.getClass("nameGenerator");
    if (!BeanNameGenerator.class.equals(generatorClass)) {
      // 指定BeanName生成器，如果有
      scanner.setBeanNameGenerator(BeanUtils.instantiateClass(generatorClass));
    }
    Class<? extends MapperFactoryBean> mapperFactoryBeanClass = annoAttrs.getClass("factoryBean");
    if (!MapperFactoryBean.class.equals(mapperFactoryBeanClass)) {
      scanner.setMapperFactoryBean(BeanUtils.instantiateClass(mapperFactoryBeanClass));
    }
    scanner.setSqlSessionTemplateBeanName(annoAttrs.getString("sqlSessionTemplateRef"));
    scanner.setSqlSessionFactoryBeanName(annoAttrs.getString("sqlSessionFactoryRef"));
    List<String> basePackages = new ArrayList<String>();
    for (String pkg : annoAttrs.getStringArray("value")) {
      if (StringUtils.hasText(pkg)) {
        basePackages.add(pkg);
      }
    }
    for (String pkg : annoAttrs.getStringArray("basePackages")) {
      if (StringUtils.hasText(pkg)) {
        basePackages.add(pkg);
      }
    }
    for (Class<?> clazz : annoAttrs.getClassArray("basePackageClasses")) {
      basePackages.add(ClassUtils.getPackageName(clazz));
    }
    // 注册过滤器，定义Bean的扫描规则
    scanner.registerFilters();
    // 开始扫描
    scanner.doScan(StringUtils.toStringArray(basePackages));
  }
  /**
* {@inheritDoc}
*/
  @Override
  public void setResourceLoader(ResourceLoader resourceLoader) {
    this.resourceLoader = resourceLoader;
  }
}

@Override
  public Set<BeanDefinitionHolder> doScan(String... basePackages) {
    // 父类完成扫描，得到一组BeanDefinition
    Set<BeanDefinitionHolder> beanDefinitions = super.doScan(basePackages);
    if (beanDefinitions.isEmpty()) {
      // 没有符合的Bean，不做处理
      logger.warn("No MyBatis mapper was found in '" + Arrays.toString(basePackages) + "' package. Please check your configuration.");
    } else {
      // 处理BeanDefinition，因为Mapper接口不能被实例化
      processBeanDefinitions(beanDefinitions);
    }
    return beanDefinitions;
  }

private void processBeanDefinitions(Set<BeanDefinitionHolder> beanDefinitions) {
  GenericBeanDefinition definition;
  for (BeanDefinitionHolder holder : beanDefinitions) {
    definition = (GenericBeanDefinition) holder.getBeanDefinition();
    // MapperFactoryBean构造函数需要MapperClass
    // 这里是告诉Spring实例化MapperFactoryBean时构造函数传哪个Class
    definition.getConstructorArgumentValues().addGenericArgumentValue(definition.getBeanClassName());
    // 重设beanClass 指向MapperFactoryBean
    definition.setBeanClass(this.mapperFactoryBean.getClass());
    definition.getPropertyValues().add("addToConfig", this.addToConfig);
    boolean explicitFactoryUsed = false;
    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;
    }
    if (StringUtils.hasText(this.sqlSessionTemplateBeanName)) {
      if (explicitFactoryUsed) {
        logger.warn("Cannot use both: sqlSessionTemplate and sqlSessionFactory together. sqlSessionFactory is ignored.");
      }
      definition.getPropertyValues().add("sqlSessionTemplate", new RuntimeBeanReference(this.sqlSessionTemplateBeanName));
      explicitFactoryUsed = true;
    } else if (this.sqlSessionTemplate != null) {
      if (explicitFactoryUsed) {
        logger.warn("Cannot use both: sqlSessionTemplate and sqlSessionFactory together. sqlSessionFactory is ignored.");
      }
      definition.getPropertyValues().add("sqlSessionTemplate", this.sqlSessionTemplate);
      explicitFactoryUsed = true;
    }
    if (!explicitFactoryUsed) {
      if (logger.isDebugEnabled()) {
        logger.debug("Enabling autowire by type for MapperFactoryBean with name '" + holder.getBeanName() + "'.");
      }
      definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE);
    }
  }
}

@Override
  public T getObject() throws Exception {
    // 基于Mapper接口生成代理对象
    return getSqlSession().getMapper(this.mapperInterface);
}