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

@Override
  public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
    AnnotationAttributes annoAttrs = AnnotationAttributes.fromMap(importingClassMetadata.getAnnotationAttributes(MapperScan.class.getName()));
    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)) {
      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)) {
      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));
    }
    scanner.registerFilters();
    scanner.doScan(StringUtils.toStringArray(basePackages));
  }

 private void processBeanDefinitions(Set<BeanDefinitionHolder> beanDefinitions) {
    GenericBeanDefinition definition;
    //遍歷bean定義
    for (BeanDefinitionHolder holder : beanDefinitions) {
       //BeanDefinitionHolder會包裝一個BeanDefinition
      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
	//此處把bean定義的構造方法中加一個參數(shù)
	//其實后面調用的MapperFactoryBean的這個構造方法，這個構造方法需要一個class。這個class就是掃描出來的Mapper的class
	//public MapperFactoryBean(Class<T> mapperInterface) {
	 //   this.mapperInterface = mapperInterface;
	 // }      
 definition.getConstructorArgumentValues().addGenericArgumentValue(definition.getBeanClassName()); // issue #59
// 此處會把   beanClass替換為MapperFactoryBean.class，后續(xù)spring進行初始化的時候就會通過MapperFactoryBean.class進行反射
  definition.setBeanClass(this.mapperFactoryBean.getClass());
//添加參數(shù)
      definition.getPropertyValues().add("addToConfig", this.addToConfig);
//下面的if沒有設置一般都不會進入
      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() + "'.");
        }
    //設置@autowire的方式為class
        definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE);
      }
    }
  }

  @Override
  public T getObject() throws Exception {
  //會返回一個MapperProxy的類，Spring就會把MapperProxy注冊到容器中，當使用Mapper的類型獲取bean的時候其實spring返回的是一個MapperProxy代理對象。
    return getSqlSession().getMapper(this.mapperInterface);
  }

  public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
    final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type);
    if (mapperProxyFactory == null) {
      throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
    }
    try {
      return mapperProxyFactory.newInstance(sqlSession);
    } catch (Exception e) {
      throw new BindingException("Error getting mapper instance. Cause: " + e, e);
    }
  }

public class MapperProxyFactory<T> {
//mapper接口的class
  private final Class<T> mapperInterface;
  //MapperMethod緩存
  private final Map<Method, MapperMethod> methodCache = new ConcurrentHashMap<Method, MapperMethod>();
  public MapperProxyFactory(Class<T> mapperInterface) {
    this.mapperInterface = mapperInterface;
  }
  public Class<T> getMapperInterface() {
    return mapperInterface;
  }
  public Map<Method, MapperMethod> getMethodCache() {
    return methodCache;
  }
  @SuppressWarnings("unchecked")
  protected T newInstance(MapperProxy<T> mapperProxy) {
  //使用JDK動態(tài)代理為mapperInterface創(chuàng)建一個mapperProxy的動態(tài)代理，后續(xù)調用mapperInterface方法的時候會進入mapperProxy的invoke方法。invoke會代理mapperInterface的方法調用。
    return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
  }
  public T newInstance(SqlSession sqlSession) {
  //new一個MapperProxy代理對象
    final MapperProxy<T> mapperProxy = new MapperProxy<T>(sqlSession, mapperInterface, methodCache);
    return newInstance(mapperProxy);
  }
}

public class MapperProxy<T> implements InvocationHandler, Serializable {
  private static final long serialVersionUID = -6424540398559729838L;
  private final SqlSession sqlSession;
  private final Class<T> mapperInterface;
  private final Map<Method, MapperMethod> methodCache;
  public MapperProxy(SqlSession sqlSession, Class<T> mapperInterface, Map<Method, MapperMethod> methodCache) {
    this.sqlSession = sqlSession;
    this.mapperInterface = mapperInterface;
    this.methodCache = methodCache;
  }
  @Override
  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    try {
    //代理的對象是否為實體類
      if (Object.class.equals(method.getDeclaringClass())) {
        return method.invoke(this, args);
      } else if (isDefaultMethod(method)) {//是否為接口的default方法
        return invokeDefaultMethod(proxy, method, args);
      }
    } catch (Throwable t) {
      throw ExceptionUtil.unwrapThrowable(t);
    }
    //接口Mapper一般都是進入這里，這邊會用一個MapperMethod進行調用，里面其實就是一個sqlSeesion的調用。
    final MapperMethod mapperMethod = cachedMapperMethod(method);
    return mapperMethod.execute(sqlSession, args);
  }