在spring中使用mybatis时一般有下面的配置
<bean id="mapperScannerConfigurer" class="org.mybatis.spring.mapper.MapperScannerConfigurer"> <property name="basePackage" value="org.xuan.springmvc.mapper,org.xuan.springxxx.mapper"/> </bean>
查看注入的MapperScannerConfigurer实现
public class MapperScannerConfigurer implements BeanDefinitionRegistryPostProcessor, InitializingBean, ApplicationContextAware, BeanNameAware { ...... }
发现继承了BeanDefinitionRegistryPostProcessor,
注:BeanDefinitionRegistryPostProcessor继承自BeanFactoryPostProcessor,其中有两个接口,postProcessBeanDefinitionRegistry是BeanDefinitionRegistryPostProcessor自带的,postProcessBeanFactory是从BeanFactoryPostProcessor继承过来的。postProcessBeanDefinitionRegistry是在所有Bean定义信息将要被加载,Bean实例还未创建的时候执行,优先postProcessBeanFactory执行。可以在BeanDefinitionRegistryPostProcessor的实现类中增加或者修改bean定义。
所以在初始化spring容器的时候会调用MapperScannerConfigurer#postProcessBeanDefinitionRegistry
@Override public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) { if (this.processPropertyPlaceHolders) { 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, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS)); }
跟踪ClassPathMapperScanner#scan
@Override public Set<BeanDefinitionHolder> doScan(String... basePackages) { //扫描相关包下面的接口 Set<BeanDefinitionHolder> beanDefinitions = super.doScan(basePackages); if (beanDefinitions.isEmpty()) { logger.warn("No MyBatis mapper was found in '" + Arrays.toString(basePackages) + "' package. Please check your configuration."); } else { //配置相关参数 processBeanDefinitions(beanDefinitions); } return beanDefinitions; }
在扫描完接口后,会配置一下接口的参数
private void processBeanDefinitions(Set<BeanDefinitionHolder> beanDefinitions) { GenericBeanDefinition definition; for (BeanDefinitionHolder holder : beanDefinitions) { 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 //配置参数,在实例化mapperFactoryBean的时候传入,也是接口的类型 definition.getConstructorArgumentValues().addGenericArgumentValue(definition.getBeanClassName()); // issue #59 //定义BeanClass,mapperFactoryBean是一个FactoryBean,(对于FactoryBean类型的Bean,在注入对象的时候是调用的getObject创建对象) definition.setBeanClass(this.mapperFactoryBean.getClass()); 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) { 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() + "'."); } definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE); } } }
注意红色的部分,就是spring管理mybatis的关键,可以去了解FactoryBean的用法(可以简单理解为产生对象的bean,在注入这种类型的对象的时候是调用自己实现的getObject来创建的)。
跟踪MapperFactoryBean
public class MapperFactoryBean<T> extends SqlSessionDaoSupport implements FactoryBean<T> { private Class<T> mapperInterface; private boolean addToConfig = true; public MapperFactoryBean() { //intentionally empty } public MapperFactoryBean(Class<T> mapperInterface) { //把前面配置的对应的mapper接口传进来 this.mapperInterface = mapperInterface; } /** * {@inheritDoc} */ @Override protected void checkDaoConfig() { super.checkDaoConfig(); notNull(this.mapperInterface, "Property 'mapperInterface' is required"); //创建完成后,看是否在configuration的mapperRegistry中,没有就添加 Configuration configuration = getSqlSession().getConfiguration(); if (this.addToConfig && !configuration.hasMapper(this.mapperInterface)) { try { configuration.addMapper(this.mapperInterface); } catch (Exception e) { logger.error("Error while adding the mapper '" + this.mapperInterface + "' to configuration.", e); throw new IllegalArgumentException(e); } finally { ErrorContext.instance().reset(); } } } /** * {@inheritDoc} */ @Override public T getObject() throws Exception { //通过SqlSession创建实例对象 return getSqlSession().getMapper(this.mapperInterface); } /** * {@inheritDoc} */ @Override public Class<T> getObjectType() { //在实例化对象的时候判断配置是哪一个mapper接口 return this.mapperInterface; } ...... }
这样就把创建接口对象又返回到mybatis中进行管理了
跟踪getSqlSession().getMapper(this.mapperInterface);最后进入了MapperRegistry#getMapper
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); } }
继续MapperProxyFactory#newInstance
protected T newInstance(MapperProxy<T> mapperProxy) { return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy); } public T newInstance(SqlSession sqlSession) { final MapperProxy<T> mapperProxy = new MapperProxy<T>(sqlSession, mapperInterface, methodCache); return newInstance(mapperProxy); }
所以其实我们最后得到的对象其实是MapperProxy的代理对象。在代码中查看mapper对象
发现和分析的一直。