Spring整合Mybatis有两个大版本，分别是1.3.2版本和2.0.5版本
先看1.3.2版本

一、1.3.2版本

先上代码

  1. @ComponentScan(value = "com.test")
  2. @MapperScan("com.test")
  3. public class AppConfig { 
  4. }
  1. @Retention(RetentionPolicy.RUNTIME)
  2. @Target(ElementType.TYPE)
  3. @Documented
  4. @Import(MapperScannerRegistrar.class)
  5. public @interface MapperScan {
  6. }

通过添加MapperScan注解，导入MapperScannerRegistrar类，下面分析MapperScannerRegistrar类

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

MapperScannerRegistrar类实现了ImportBeanDefinitionRegistrar接口，Spring在启动的时候就会调用MapperScannerRegistrar类的registerBeanDefinitions方法，registerBeanDefinitions方法中定义了一个ClassPathMapperScanner对象，这个对象会扫描指定包下的mapper接口，然而Spring默认是不扫描接口的，
Mybatis重写了isCandidateComponent方法，代码如下

  1. @Override
  2.   protected boolean isCandidateComponent(AnnotatedBeanDefinition beanDefinition) {
  3.     return beanDefinition.getMetadata().isInterface() && beanDefinition.getMetadata().isIndependent();
  4.   }

从上面代码可以看出Mybatis只扫描接口。然后通过Spring扫描后，会把扫描出来的接口封装成对应的BeanDefinition,接下来把BeanDefinition进行修改，将BeanClass设置成MapperFactoryBean，把注入模式修改为ByType。

  1. private void processBeanDefinitions(Set<BeanDefinitionHolder> beanDefinitions) {
  2.     GenericBeanDefinition definition;
  3.     for (BeanDefinitionHolder holder : beanDefinitions) {
  4.       definition = (GenericBeanDefinition) holder.getBeanDefinition();
  6.       if (logger.isDebugEnabled()) {
  7.         logger.debug("Creating MapperFactoryBean with name '" + holder.getBeanName() 
  8.           + "' and '" + definition.getBeanClassName() + "' mapperInterface");
  9.       }
  11.       // the mapper interface is the original class of the bean
  12.       // but, the actual class of the bean is MapperFactoryBean
  13.       definition.getConstructorArgumentValues().addGenericArgumentValue(definition.getBeanClassName()); // issue #59
  14.       // 将BeanDefinition的BeanClass设置成MapperFactoryBean
  15.         definition.setBeanClass(this.mapperFactoryBean.getClass());
  17.       definition.getPropertyValues().add("addToConfig", this.addToConfig);
  19.       boolean explicitFactoryUsed = false;
  20.       if (StringUtils.hasText(this.sqlSessionFactoryBeanName)) {
  21.         definition.getPropertyValues().add("sqlSessionFactory", new RuntimeBeanReference(this.sqlSessionFactoryBeanName));
  22.         explicitFactoryUsed = true;
  23.       } else if (this.sqlSessionFactory != null) {
  24.         definition.getPropertyValues().add("sqlSessionFactory", this.sqlSessionFactory);
  25.         explicitFactoryUsed = true;
  26.       }
  28.       if (StringUtils.hasText(this.sqlSessionTemplateBeanName)) {
  29.         if (explicitFactoryUsed) {
  30.           logger.warn("Cannot use both: sqlSessionTemplate and sqlSessionFactory together. sqlSessionFactory is ignored.");
  31.         }
  32.         definition.getPropertyValues().add("sqlSessionTemplate", new RuntimeBeanReference(this.sqlSessionTemplateBeanName));
  33.         explicitFactoryUsed = true;
  34.       } else if (this.sqlSessionTemplate != null) {
  35.         if (explicitFactoryUsed) {
  36.           logger.warn("Cannot use both: sqlSessionTemplate and sqlSessionFactory together. sqlSessionFactory is ignored.");
  37.         }
  38.         definition.getPropertyValues().add("sqlSessionTemplate", this.sqlSessionTemplate);
  39.         explicitFactoryUsed = true;
  40.       }
  42.       if (!explicitFactoryUsed) {
  43.         if (logger.isDebugEnabled()) {
  44.           logger.debug("Enabling autowire by type for MapperFactoryBean with name '" + holder.getBeanName() + "'.");
  45.         }
  46.           // 修改注入模型为ByType
  47.         definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE);
  48.       }
  49.     }
  50.   }

扫描完成后会，Spring会根据BeanDefinition去创建Bean对象，相当于每个Mapper对应一个BeanFactory，
在MapperBeanFactory的getObject方法中调用了getSqlSession方法去得到一个SqlSession对象，然后根据对应的Mapper接口生成一个代理对象。

  1. @Override
  2. public T getObject() throws Exception {
  3.     return getSqlSession().getMapper(this.mapperInterface);
  4. }

sqlSession对象是Mybatis中的，一个sqlSession对象需要SqlSessionFactory来产生，由于上面已经将BeanDefinition的注入模型为ByType,所以Spring会自动调用set方法，有两个set方法，一个setSqlSessionFactory，一个setSqlSessionTemplate，而这两个方法执行的前提是根据方法参数类型能找到对应的bean，所以Spring容器中要存在SqlSessionFactory类型的bean或者SqlSessionTemplate类型的bean。

二、2.0.5版本

  • 通过@MapperScan导入了MapperScannerRegistrar类
  • MapperScannerRegistrar类实现了ImportBeanDefinitionRegistrar接口，所以Spring在启动时会调用MapperScannerRegistrar类中的registerBeanDefinitions方法
  • 在registerBeanDefinitions方法中生成了一个MapperScannerConfigurer类型的BeanDefinition
  • 而MapperScannerConfigurer实现了实现了BeanDefinitionRegistryPostProcessor接口，所以Spring在启动过程中时会调用它的postProcessBeanDefinitionRegistry()方法
  • 在postProcessBeanDefinitionRegistry方法中会生成一个ClassPathMapperScanner对象，然后进行扫描
  • 后续的逻辑和1.3.2版本一样。

带来的好处是，可以不使用@MapperScan注解，而可以直接定义一个Bean，比如：

  1. @Bean
  2. public MapperScannerConfigurer mapperScannerConfigurer() {
  3.     MapperScannerConfigurer mapperScannerConfigurer = new MapperScannerConfigurer();
  4.     mapperScannerConfigurer.setBasePackage("com.test");
  5.     return mapperScannerConfigurer;
  6. }