1、mybatis源码学习@Mapper注解

1、@Mapper自动配置的程序入口在 MybatisAutoConfiguration类的最下面，
（mybatis-spring-boot-autoconfigure-x.x.x.jar，org.mybatis.spring.boot.autoconfigure.MybatisAutoConfiguration中的内部类实现）
根据名字可以看出，这个是自动配置，用到了spring-boot的自动配置相关注解

@org.springframework.context.annotation.Configuration
//Import注解引入 @Mapper扫描类
@Import({ AutoConfiguredMapperScannerRegistrar.class })
@ConditionalOnMissingBean(MapperFactoryBean.class)
public static class MapperScannerRegistrarNotFoundConfiguration {

  @PostConstruct
  public void afterPropertiesSet() {
    logger.debug("No {} found.", MapperFactoryBean.class.getName());
  }
}

上面代码的逻辑是 如果标注了@MapperScan 的注解，将会生成 MapperFactoryBean， 如果没有标注@MapperScan 也就是没有MapperFactoryBean的实例，就走@Import里面的配置，下面看看AutoConfiguredMapperScannerRegistrar的配置，它是MybatisAutoConfiguration类下的内部类

  public static class AutoConfiguredMapperScannerRegistrar
      implements BeanFactoryAware, ImportBeanDefinitionRegistrar, ResourceLoaderAware {

    private BeanFactory beanFactory;

    private ResourceLoader resourceLoader;

    @Override
    public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {

      logger.debug("Searching for mappers annotated with @Mapper");
	  //初始化ClassPathMapperScanner扫描器,扫描器继承了spirng的ClassPathBeanDefinitionScanner
	  //的主要作用就是扫描@Mapper注解的类进行配置并注册为spring bean
      ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry);

      try {
        if (this.resourceLoader != null) {
          scanner.setResourceLoader(this.resourceLoader);
        }

        List<String> packages = AutoConfigurationPackages.get(this.beanFactory);
        if (logger.isDebugEnabled()) {
          for (String pkg : packages) {
            logger.debug("Using auto-configuration base package '{}'", pkg);
          }
        }

        scanner.setAnnotationClass(Mapper.class);
        scanner.registerFilters();
        scanner.doScan(StringUtils.toStringArray(packages));
      } catch (IllegalStateException ex) {
        logger.debug("Could not determine auto-configuration package, automatic mapper scanning disabled.", ex);
      }
    }

    @Override
    public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
      this.beanFactory = beanFactory;
    }

    @Override
    public void setResourceLoader(ResourceLoader resourceLoader) {
      this.resourceLoader = resourceLoader;
    }
  }

2、首先看看核心的doScan()方法
这个类主要就是调用父类ClassPathBeanDefinitionScanner中的doScan()方法，获取所有的类定义，之后添加自己的逻辑：processBeanDefinitions（）

public Set<BeanDefinitionHolder> doScan(String... basePackages) {
  Set<BeanDefinitionHolder> beanDefinitions = super.doScan(basePackages);

  if (beanDefinitions.isEmpty()) {
    logger.warn("No MyBatis mapper was found in '" + Arrays.toString(basePackages) + "' package. Please check your configuration.");
  } else {
    processBeanDefinitions(beanDefinitions);
  }

  return beanDefinitions;
}

3、将beanDefinition中的beanClass替换为MapperFactoryBean.class，实例化对象的时候，就会调用MapperFactoryBean的getObject方法获取代理对象，然后交由spring容器管理

private void processBeanDefinitions(Set<BeanDefinitionHolder> beanDefinitions) {
  GenericBeanDefinition definition;
  for (BeanDefinitionHolder holder : beanDefinitions) {
    definition = (GenericBeanDefinition) holder.getBeanDefinition();

    if (logger.isDebugEnabled()) {
      logger.debug("Creating MapperFactoryBean with name '" + holder.getBeanName() 
        + "' and '" + definition.getBeanClassName() + "' mapperInterface");
    }

    // the mapper interface is the original class of the bean
    // but, the actual class of the bean is MapperFactoryBean
    definition.getConstructorArgumentValues().addGenericArgumentValue(definition.getBeanClassName()); // issue #59
    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);
    }
  }
}

来源：CSDN

作者：怎么这么饿

链接：https://blog.csdn.net/qq_29082261/article/details/103989460