之前看了Spring源码之后，对Spring+MyBatis项目有个疑问，Dao层的mapper接口上@repository有时候却不用写，难道mapper包扫描生成代理类发生在service层的依赖注入之前吗？要不然service层的类@Autowired mapper接口时会找不到实例啊？
后面读了MyBatis Spring 集成源码MapperScannerConfigurer后解决了疑问。
先看一下MapperScannerConfigurer
Mybatis MapperScannerConfigurer 自动扫描 将Mapper接口生成代理注入到Spring
MapperFactoryBean的出现为了代替手工使用SqlSessionDaoSupport或SqlSessionTemplate编写数据访问对象(DAO)的代码,使用动态代理实现。
比如下面这个官方文档中的配置：
<bean id="userMapper" class="org.mybatis.spring.mapper.MapperFactoryBean">
<property name="mapperInterface" value="org.mybatis.spring.sample.mapper.UserMapper" />
<property name="sqlSessionFactory" ref="sqlSessionFactory" />
</bean>org.mybatis.spring.sample.mapper.UserMapper是一个接口，我们创建一个MapperFactoryBean实例，然后注入这个接口和sqlSessionFactory（mybatis中提供的SqlSessionFactory接口，MapperFactoryBean会使用SqlSessionFactory创建SqlSession）这两个属性。
之后想使用这个UserMapper接口的话，直接通过spring注入这个bean，然后就可以直接使用了，spring内部会创建一个这个接口的动态代理。
当发现要使用多个MapperFactoryBean的时候，一个一个定义肯定非常麻烦，于是mybatis-spring提供了MapperScannerConfigurer这个类，它将会查找类路径下的映射器并自动将它们创建成MapperFactoryBean。
<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
<property name="basePackage" value="org.mybatis.spring.sample.mapper" />
</bean>这段配置会扫描org.mybatis.spring.sample.mapper下的所有接口，然后创建各自接口的动态代理类。
与Spring集成可以分为3个步骤.
1. 把Java类对应的Mapper接口类纳入Spring中的IOC容器管理。
2. 把Java类对应的XML命名空间添加到Mybatis中的Configuration类中的mapperRegistry(用于管理Mybatis的Mapper).
3. 使用Spring中的IOC容器扩展FactoryBean获取到Mapper的实例。(第一步纳入Spring只是接口)
下面看一下MapperScannerConfigurer源码：
先看一下类的继承关系
public class MapperScannerConfigurer implements BeanDefinitionRegistryPostProcessor,
InitializingBean, ApplicationContextAware, BeanNameAware实现了BeanDefinitionRegistryPostProcessor接口
public interface BeanDefinitionRegistryPostProcessor extends BeanFactoryPostProcessor {
void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry var1) throws BeansException;
}BeanDefinitionRegistryPostProcessor接口继承了BeanFactoryPostProcessor
BeanDefinitionRegistryPostProcessor spring官方解释是:允许在正常的BeanFactoryPostProcessor检测开始之前注册更多的自定义bean。特别是，BeanDefinitionRegistryPostProcessor可以注册更多的bean定义，然后定义BeanFactoryPostProcessor实例。也就是说可以借此方法实现自定义的bean。
BeanDefinitionRegistryPostProcessor继承了BeanFactoryPostProcessor, 也就是说想实现自定义的bean 可以实现BeanDefinitionRegistryPostProcessor或者BeanFactoryPostProcessor中的方法。
下面看一下MapperScannerConfigurer中实现BeanDefinitionRegistryPostProcessor中的postProcessBeanDefinitionRegistry方法：
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
if (this.processPropertyPlaceHolders) {
this.processPropertyPlaceHolders();
}
ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry);
scanner.setAddToConfig(this.addToConfig);
scanner.setAnnotationClass(this.annotationClass);
scanner.setMarkerInterface(this.markerInterface);
scanner.setSqlSessionFactory(this.sqlSessionFactory);
scanner.setSqlSessionTemplate(this.sqlSessionTemplate);
scanner.setSqlSessionFactoryBeanName(this.sqlSessionFactoryBeanName);
scanner.setSqlSessionTemplateBeanName(this.sqlSessionTemplateBeanName);
scanner.setResourceLoader(this.applicationContext);
scanner.setBeanNameGenerator(this.nameGenerator);
scanner.registerFilters();
scanner.scan(StringUtils.tokenizeToStringArray(this.basePackage, ",; \t\n"));
}scan方法调用的是类ClassPathBeanDefinitionScanner的scan方法
public int scan(String... basePackages) {
int beanCountAtScanStart = this.registry.getBeanDefinitionCount();
this.doScan(basePackages);
if (this.includeAnnotationConfig) {
AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);
}
return this.registry.getBeanDefinitionCount() - beanCountAtScanStart;
}
protected Set<BeanDefinitionHolder> doScan(String... basePackages) {
Assert.notEmpty(basePackages, "At least one base package must be specified");
Set<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet();
String[] var3 = basePackages;
int var4 = basePackages.length;
for(int var5 = 0; var5 < var4; ++var5) {
String basePackage = var3[var5];
Set<BeanDefinition> candidates = this.findCandidateComponents(basePackage);
Iterator var8 = candidates.iterator();
while(var8.hasNext()) {
BeanDefinition candidate = (BeanDefinition)var8.next();
ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate);
candidate.setScope(scopeMetadata.getScopeName());
String beanName = this.beanNameGenerator.generateBeanName(candidate, this.registry);
if (candidate instanceof AbstractBeanDefinition) {
this.postProcessBeanDefinition((AbstractBeanDefinition)candidate, beanName);
}
if (candidate instanceof AnnotatedBeanDefinition) {
AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition)candidate);
}
if (this.checkCandidate(beanName, candidate)) {
BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName);
definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
beanDefinitions.add(definitionHolder);
this.registerBeanDefinition(definitionHolder, this.registry);
}
}
}
return beanDefinitions;
}第三行this.doScan(basePackages)调用的并不是本类的doScan方法，而是ClassPathMapperScanner的doScan方法
两个类的关系：
class ClassPathMapperScanner extends ClassPathBeanDefinitionScanner
public Set<BeanDefinitionHolder> doScan(String... basePackages) {
Set<BeanDefinitionHolder> beanDefinitions = super.doScan(basePackages);
if (beanDefinitions.isEmpty()) {
this.logger.warn("No MyBatis mapper was found in '" + Arrays.toString(basePackages) + "' package. Please check your configuration.");
} else {
Iterator i$ = beanDefinitions.iterator();
while(i$.hasNext()) {
BeanDefinitionHolder holder = (BeanDefinitionHolder)i$.next();
GenericBeanDefinition definition = (GenericBeanDefinition)holder.getBeanDefinition();
if (this.logger.isDebugEnabled()) {
this.logger.debug("Creating MapperFactoryBean with name '" + holder.getBeanName() + "' and '" + definition.getBeanClassName() + "' mapperInterface");
}
definition.getPropertyValues().add("mapperInterface", definition.getBeanClassName());
definition.setBeanClass(MapperFactoryBean.class);
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) {
this.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) {
this.logger.warn("Cannot use both: sqlSessionTemplate and sqlSessionFactory together. sqlSessionFactory is ignored.");
}
definition.getPropertyValues().add("sqlSessionTemplate", this.sqlSessionTemplate);
explicitFactoryUsed = true;
}
if (!explicitFactoryUsed) {
if (this.logger.isDebugEnabled()) {
this.logger.debug("Enabling autowire by type for MapperFactoryBean with name '" + holder.getBeanName() + "'.");
}
definition.setAutowireMode(2);
}
}
}
return beanDefinitions;
}第二行Set<BeanDefinitionHolder> beanDefinitions = super.doScan(basePackages);调用的又是类ClassPathBeanDefinitionScanner的doScan方法
