接上一篇文章：https://blog.csdn.net/qq_26437925/article/details/145100531， 本文注解分析mybatis-spring中的@MapperScan注解，则将容易许多。

@MapperScan注解定义

@MapperScan注解加入了@Import(MapperScannerRegistrar.class)， 所以可以知晓

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
@Import(MapperScannerRegistrar.class)
public @interface MapperScan {

  /**
   * Alias for the {@link #basePackages()} attribute. Allows for more concise
   * annotation declarations e.g.:
   * {@code @EnableMyBatisMapperScanner("org.my.pkg")} instead of {@code
   * @EnableMyBatisMapperScanner(basePackages= "org.my.pkg"})}.
   */
  String[] value() default {};

  /**
   * Base packages to scan for MyBatis interfaces. Note that only interfaces
   * with at least one method will be registered; concrete classes will be
   * ignored.
   */
  String[] basePackages() default {};

  /**
   * Type-safe alternative to {@link #basePackages()} for specifying the packages
   * to scan for annotated components. The package of each class specified will be scanned.
   * <p>Consider creating a special no-op marker class or interface in each package
   * that serves no purpose other than being referenced by this attribute.
   */
  Class<?>[] basePackageClasses() default {};

  /**
   * The {@link BeanNameGenerator} class to be used for naming detected components
   * within the Spring container.
   */
  Class<? extends BeanNameGenerator> nameGenerator() default BeanNameGenerator.class;

  /**
   * This property specifies the annotation that the scanner will search for.
   * <p>
   * The scanner will register all interfaces in the base package that also have
   * the specified annotation.
   * <p>
   * Note this can be combined with markerInterface.
   */
  Class<? extends Annotation> annotationClass() default Annotation.class;

  /**
   * This property specifies the parent that the scanner will search for.
   * <p>
   * The scanner will register all interfaces in the base package that also have
   * the specified interface class as a parent.
   * <p>
   * Note this can be combined with annotationClass.
   */
  Class<?> markerInterface() default Class.class;

  /**
   * Specifies which {@code SqlSessionTemplate} to use in the case that there is
   * more than one in the spring context. Usually this is only needed when you
   * have more than one datasource.
   */
  String sqlSessionTemplateRef() default "";

  /**
   * Specifies which {@code SqlSessionFactory} to use in the case that there is
   * more than one in the spring context. Usually this is only needed when you
   * have more than one datasource.
   */
  String sqlSessionFactoryRef() default "";

  /**
   * Specifies a custom MapperFactoryBean to return a mybatis proxy as spring bean.
   *
   */
  Class<? extends MapperFactoryBean> factoryBean() default MapperFactoryBean.class;

}

ConfigurationClassPostProcessor扫描注册beanDefinition

mybatis-spring中自定义了org.mybatis.spring.annotation.MapperScannerRegistrar实现了ImportBeanDefinitionRegistrar接口，所以能被处理

mybatis-spring也实现了自己的Scanner能够扫描出所有的@Mapper的interface, 然后定义出BeanDefinition

继续debug可以看到对BeanDefinisiton 会设置BeanClass为FactoryBean类

即自定义的org.mybatis.spring.mapper.MapperFactoryBean

org.mybatis.spring.mapper.MapperFactoryBean

仍然是重点关注getObject方法

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

数据库操作也封装为SqlSession接口，有多个实现类可选择

最后也会发现是java 动态代理

org.apache.ibatis.binding.MapperProxy

代理的具体实现则在mybatis依赖的MapperProxy类中

@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
  try {
    if (Object.class.equals(method.getDeclaringClass())) {
      return method.invoke(this, args);
    } else if (isDefaultMethod(method)) {
      return invokeDefaultMethod(proxy, method, args);
    }
  } catch (Throwable t) {
    throw ExceptionUtil.unwrapThrowable(t);
  }
  final MapperMethod mapperMethod = cachedMapperMethod(method);
  return mapperMethod.execute(sqlSession, args);
}

sql执行

public Object execute(SqlSession sqlSession, Object[] args) {
  Object result;
  switch (command.getType()) {
    case INSERT: {
    Object param = method.convertArgsToSqlCommandParam(args);
      result = rowCountResult(sqlSession.insert(command.getName(), param));
      break;
    }
    case UPDATE: {
      Object param = method.convertArgsToSqlCommandParam(args);
      result = rowCountResult(sqlSession.update(command.getName(), param));
      break;
    }
    case DELETE: {
      Object param = method.convertArgsToSqlCommandParam(args);
      result = rowCountResult(sqlSession.delete(command.getName(), param));
      break;
    }
    case SELECT:
      if (method.returnsVoid() && method.hasResultHandler()) {
        executeWithResultHandler(sqlSession, args);
        result = null;
      } else if (method.returnsMany()) {
        result = executeForMany(sqlSession, args);
      } else if (method.returnsMap()) {
        result = executeForMap(sqlSession, args);
      } else if (method.returnsCursor()) {
        result = executeForCursor(sqlSession, args);
      } else {
        Object param = method.convertArgsToSqlCommandParam(args);
        result = sqlSession.selectOne(command.getName(), param);
      }
      break;
    case FLUSH:
      result = sqlSession.flushStatements();
      break;
    default:
      throw new BindingException("Unknown execution method for: " + command.getName());
  }
  if (result == null && method.getReturnType().isPrimitive() && !method.returnsVoid()) {
    throw new BindingException("Mapper method '" + command.getName() 
        + " attempted to return null from a method with a primitive return type (" + method.getReturnType() + ").");
  }
  return result;
}

org.apache.ibatis.executor.SimpleExecutor#doUpdate

继续深入找一个简单的sql执行实现类，可以看到类似jdbc的处理流程

总结

最后还是回到了上一篇博文：https://blog.csdn.net/qq_26437925/article/details/145100531。只不过mybatis-spring要丰富一些，原理仍然是动态代理，BeanFactoryPostProcessor ，FactoryBean，BeanPostProcessor这些基础知识。