在SpringBoot中，可以通过两种方式加载Mapper接口。

  • 通过MapperScan注解的方式加载mapper接口。
  • 如果没有注入任何的MapperFactoryBean，则使用@Mapper注解的单个注入方式。

加载Mapper接口 - 图1

@MapperScan注解

  1. @Retention(RetentionPolicy.RUNTIME)
  2. @Target(ElementType.TYPE)
  3. @Documented
  4. @Import(MapperScannerRegistrar.class)
  5. public @interface MapperScan {
  6.     //other code...
  7. }

如果使用了@MapperScan注解，则会使用MapperScannerRegistrar加载Mapper。

  1. public class MapperScannerRegistrar implements ImportBeanDefinitionRegistrar, ResourceLoaderAware {
  3.     private ResourceLoader resourceLoader;
  5.     @Override
  6.     public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
  8.         AnnotationAttributes annoAttrs = AnnotationAttributes.fromMap(importingClassMetadata.getAnnotationAttributes(MapperScan.class.getName()));
  9.         ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry);
  11.         // this check is needed in Spring 3.1
  12.         if (resourceLoader != null) {
  13.             scanner.setResourceLoader(resourceLoader);
  14.         }
  16.         Class<? extends Annotation> annotationClass = annoAttrs.getClass("annotationClass");
  17.         if (!Annotation.class.equals(annotationClass)) {
  18.             scanner.setAnnotationClass(annotationClass);
  19.         }
  21.         Class<?> markerInterface = annoAttrs.getClass("markerInterface");
  22.         if (!Class.class.equals(markerInterface)) {
  23.             scanner.setMarkerInterface(markerInterface);
  24.         }
  26.         Class<? extends BeanNameGenerator> generatorClass = annoAttrs.getClass("nameGenerator");
  27.         if (!BeanNameGenerator.class.equals(generatorClass)) {
  28.             scanner.setBeanNameGenerator(BeanUtils.instantiateClass(generatorClass));
  29.         }
  31.         Class<? extends MapperFactoryBean> mapperFactoryBeanClass = annoAttrs.getClass("factoryBean");
  32.         if (!MapperFactoryBean.class.equals(mapperFactoryBeanClass)) {
  33.             scanner.setMapperFactoryBean(BeanUtils.instantiateClass(mapperFactoryBeanClass));
  34.         }
  36.         scanner.setSqlSessionTemplateBeanName(annoAttrs.getString("sqlSessionTemplateRef"));
  37.         scanner.setSqlSessionFactoryBeanName(annoAttrs.getString("sqlSessionFactoryRef"));
  39.         List<String> basePackages = new ArrayList<String>();
  40.         //解析@MapperScan的属性
  41.         for (String pkg : annoAttrs.getStringArray("value")) {
  42.             if (StringUtils.hasText(pkg)) {
  43.                 basePackages.add(pkg);
  44.             }
  45.         }
  46.         for (String pkg : annoAttrs.getStringArray("basePackages")) {
  47.             if (StringUtils.hasText(pkg)) {
  48.                 basePackages.add(pkg);
  49.             }
  50.         }
  51.         for (Class<?> clazz : annoAttrs.getClassArray("basePackageClasses")) {
  52.             basePackages.add(ClassUtils.getPackageName(clazz));
  53.         }
  54.         scanner.registerFilters();
  55.         //进行包扫描
  56.         scanner.doScan(StringUtils.toStringArray(basePackages));
  57.     }
  59.     @Override
  60.     public void setResourceLoader(ResourceLoader resourceLoader) {
  61.         this.resourceLoader = resourceLoader;
  62.     }
  64. }

一旦使用@MapperScan注解，则回在MapperScannerRegistrar#registerBeanDefinitions方法中会解析@MapperScan注解的属性，加载basePackages，并进行包扫描，调用doScan方法。

  1. public class ClassPathMapperScanner extends ClassPathBeanDefinitionScanner {
  2.     //other code...
  4.     private MapperFactoryBean<?> mapperFactoryBean = new MapperFactoryBean<Object>();
  6.     @Override
  7.     public Set<BeanDefinitionHolder> doScan(String... basePackages) {
  8.         //调用父类的doScan方法
  9.         Set<BeanDefinitionHolder> beanDefinitions = super.doScan(basePackages);
  11.         if (beanDefinitions.isEmpty()) {
  12.             logger.warn("No MyBatis mapper was found in '" + Arrays.toString(basePackages) + "' package. Please check your configuration.");
  13.         } else {
  14.             //进行Bean定义
  15.             processBeanDefinitions(beanDefinitions);
  16.         }
  18.         return beanDefinitions;
  19.     }
  21.     private void processBeanDefinitions(Set<BeanDefinitionHolder> beanDefinitions) {
  22.         GenericBeanDefinition definition;
  23.         for (BeanDefinitionHolder holder : beanDefinitions) {
  24.             definition = (GenericBeanDefinition) holder.getBeanDefinition();
  26.             if (logger.isDebugEnabled()) {
  27.                 logger.debug("Creating MapperFactoryBean with name '" + holder.getBeanName()
  28.                         + "' and '" + definition.getBeanClassName() + "' mapperInterface");
  29.             }
  31.             // the mapper interface is the original class of the bean
  32.             // but, the actual class of the bean is MapperFactoryBean
  33.             definition.getConstructorArgumentValues().addGenericArgumentValue(definition.getBeanClassName()); 
  34.             //将@MapperScan扫描进来的Mapper接口的class设置为MapperFactoryBean的class
  35.             definition.setBeanClass(this.mapperFactoryBean.getClass());
  37.             definition.getPropertyValues().add("addToConfig", this.addToConfig);
  39.             boolean explicitFactoryUsed = false;
  40.             if (StringUtils.hasText(this.sqlSessionFactoryBeanName)) {
  41.                 definition.getPropertyValues().add("sqlSessionFactory", new RuntimeBeanReference(this.sqlSessionFactoryBeanName));
  42.                 explicitFactoryUsed = true;
  43.             } else if (this.sqlSessionFactory != null) {
  44.                 definition.getPropertyValues().add("sqlSessionFactory", this.sqlSessionFactory);
  45.                 explicitFactoryUsed = true;
  46.             }
  48.             if (StringUtils.hasText(this.sqlSessionTemplateBeanName)) {
  49.                 if (explicitFactoryUsed) {
  50.                     logger.warn("Cannot use both: sqlSessionTemplate and sqlSessionFactory together. sqlSessionFactory is ignored.");
  51.                 }
  52.                 definition.getPropertyValues().add("sqlSessionTemplate", new RuntimeBeanReference(this.sqlSessionTemplateBeanName));
  53.                 explicitFactoryUsed = true;
  54.             } else if (this.sqlSessionTemplate != null) {
  55.                 if (explicitFactoryUsed) {
  56.                     logger.warn("Cannot use both: sqlSessionTemplate and sqlSessionFactory together. sqlSessionFactory is ignored.");
  57.                 }
  58.                 definition.getPropertyValues().add("sqlSessionTemplate", this.sqlSessionTemplate);
  59.                 explicitFactoryUsed = true;
  60.             }
  62.             if (!explicitFactoryUsed) {
  63.                 if (logger.isDebugEnabled()) {
  64.                     logger.debug("Enabling autowire by type for MapperFactoryBean with name '" + holder.getBeanName() + "'.");
  65.                 }
  66.                 definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE);
  67.             }
  68.         }
  69.     }
  70. }

上面的代码definition.setBeanClass(this.mapperFactoryBean.getClass()); 把@MapperScan包扫描进来的Mapper接口的class设置成来MapperFactoryBean的class，所以使用@MapperScan注解的话，在容器中就存在MapperFactoryBean这个类型的Bean，从而导致MapperScannerRegistrarNotFoundConfiguration配置类不生效，原因就是类签名上有个注解@ConditionalOnMissingBean(MapperFactoryBean.class)。

@Mapper注解

在MybatisAutoConfiguration自动配置类中的静态内部类 AutoConfiguredMapperScannerRegistrar。
在 MybatisAutoConfiguration解析MapperScannerRegistrarNotFoundConfiguration时。其条件为 @ConditionalOnMissingshiBean(MapperFactoryBean.class)。

@org.springframework.context.annotation.Configuration
@ConditionalOnClass({ SqlSessionFactory.class, SqlSessionFactoryBean.class })
@ConditionalOnSingleCandidate(DataSource.class)
@EnableConfigurationProperties(MybatisProperties.class)
@AutoConfigureAfter(DataSourceAutoConfiguration.class)
public class MybatisAutoConfiguration implements InitializingBean {

  public static class AutoConfiguredMapperScannerRegistrar
      implements BeanFactoryAware, ImportBeanDefinitionRegistrar, ResourceLoaderAware {

    private BeanFactory beanFactory;

    private ResourceLoader resourceLoader;

    @Override
    public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
            //packages AutoConfigurationPackages的加载
      List<String> packages = AutoConfigurationPackages.get(this.beanFactory);
      ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry);
      if (this.resourceLoader != null) {
        scanner.setResourceLoader(this.resourceLoader);
      }
      scanner.setAnnotationClass(Mapper.class);
      scanner.registerFilters();
      scanner.doScan(StringUtils.toStringArray(packages));

    }

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

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

  @org.springframework.context.annotation.Configuration
  @Import({ AutoConfiguredMapperScannerRegistrar.class })
  @ConditionalOnMissingshiBean(MapperFactoryBean.class)
  public static class MapperScannerRegistrarNotFoundConfiguration implements InitializingBean {
    @Override
    public void afterPropertiesSet() {
      logger.debug("No {} found.", MapperFactoryBean.class.getName());
    }
  }
}