下面将结合mybatis源码来分析下，这种持久化框架是如何对connection使用，来达到spring事务的控制。
想要在把mybatis跟spring整合都需要这样一个jar包：mybatis-spring-x.x.x.jar，这里面定义了一些主要的整合信息。
在spring配置文件中需要配置如下两个bean：
<!-- mybatis配置 --> <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean"> <property name="dataSource" ref="dynamicDataSource" /> <property name="configLocation" value="classpath:mybatis.xml"></property> <!-- mybatis配置文件 --> <property name="mapperLocations" value="classpath:com/blackbread/dao/mapper/*.xml" /> </bean> <!--mapper scanning --> <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer"> <property name="basePackage" value="com.blackbread.dao" /> <property name="sqlSessionFactoryBeanName" value="sqlSessionFactory" /> </bean>
首先让我们来看org.mybatis.spring.SqlSessionFactoryBean，在这个类需要注入跟之前tx配置中一样的dataSource。
SqlSessionFactoryBean类实现了InitializingBean接口，所以会执行afterPropertiesSet方法，在afterPropertiesSet方法中会执行buildSqlSessionFactory方法生成一个sqlSessionFactory对象，让我们看下buildSqlSessionFactory方法：由于主要看的是跟spring tx结合的方式，所以代码看不上很细，如有疏漏，望不吝赐教。
protected SqlSessionFactory buildSqlSessionFactory() throws IOException { Configuration configuration; XMLConfigBuilder xmlConfigBuilder = null; //初始化一个configuration if (this.configLocation != null) { xmlConfigBuilder = new XMLConfigBuilder(this.configLocation.getInputStream(), null, this.configurationProperties); configuration = xmlConfigBuilder.getConfiguration(); } else { configuration = new Configuration(); configuration.setVariables(this.configurationProperties); } if (this.objectFactory != null) { configuration.setObjectFactory(this.objectFactory); } if (this.objectWrapperFactory != null) { configuration.setObjectWrapperFactory(this.objectWrapperFactory); } if (hasLength(this.typeAliasesPackage)) { String[] typeAliasPackageArray = tokenizeToStringArray(this.typeAliasesPackage, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS); for (String packageToScan : typeAliasPackageArray) { configuration.getTypeAliasRegistry().registerAliases(packageToScan, typeAliasesSuperType == null ? Object.class : typeAliasesSuperType); } } //设置别名 if (!isEmpty(this.typeAliases)) { for (Class<?> typeAlias : this.typeAliases) { configuration.getTypeAliasRegistry().registerAlias(typeAlias); } } //装入插件，mybatis的插件都是以拦截器的形式进行的好像，比如分页插件，这里是载入spring中注入的 if (!isEmpty(this.plugins)) { for (Interceptor plugin : this.plugins) { configuration.addInterceptor(plugin); } } if (hasLength(this.typeHandlersPackage)) { String[] typeHandlersPackageArray = tokenizeToStringArray(this.typeHandlersPackage, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS); for (String packageToScan : typeHandlersPackageArray) { configuration.getTypeHandlerRegistry().register(packageToScan); } } if (!isEmpty(this.typeHandlers)) { for (TypeHandler<?> typeHandler : this.typeHandlers) { configuration.getTypeHandlerRegistry().register(typeHandler); } } //这里将解析mybatis.xml文件，载入所有配置，插件、setting等 if (xmlConfigBuilder != null) { try { xmlConfigBuilder.parse(); } catch (Exception ex) { throw new NestedIOException("Failed to parse config resource: " + this.configLocation, ex); } finally { ErrorContext.instance().reset(); } } //这个很重要，这里定义了用的transactionFactory为SpringManagedTransactionFactory，这个在获取 //connection等地方都有用到，是mybatis跟spring的主要链接 if (this.transactionFactory == null) { this.transactionFactory = new SpringManagedTransactionFactory(); } //新建一个Environment对象，并将新建的transactionFactory放入其中 Environment environment = new Environment(this.environment, this.transactionFactory, this.dataSource); configuration.setEnvironment(environment); if (this.databaseIdProvider != null) { try { configuration.setDatabaseId(this.databaseIdProvider.getDatabaseId(this.dataSource)); } catch (SQLException e) { throw new NestedIOException("Failed getting a databaseId", e); } } if (!isEmpty(this.mapperLocations)) { for (Resource mapperLocation : this.mapperLocations) { if (mapperLocation == null) { continue; } try { //这里主要是解析配置的sql mapper配置文件 XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(mapperLocation.getInputStream(), configuration, mapperLocation.toString(), configuration.getSqlFragments()); xmlMapperBuilder.parse(); } catch (Exception e) { throw new NestedIOException("Failed to parse mapping resource: '" + mapperLocation + "'", e); } finally { ErrorContext.instance().reset(); } } } else { } } return this.sqlSessionFactoryBuilder.build(configuration); }
看着好长的一段啊，其实这里做的工作就是解析配置文件生成configuration对象而已。在
xmlMapperBuilder.parse();
这里将解析sql mapper文件中的映射关系生成MappedStatement对象，并执行 configuration.addMappedStatement(statement);放入到configuration对象中，有兴趣的同学可以仔细看下。
这里主要需要注意的一块就是this.transactionFactory = new SpringManagedTransactionFactory();这里就是mybatis跟spring连接到一起的地方。
接着我们看一下org.mybatis.spring.mapper.MapperScannerConfigurer对象的初始化过程，这个对象实现了BeanDefinitionRegistryPostProcessor接口，在postProcessBeanDefinitionRegistry方法中初始化一个对象ClassPathMapperScanner，并讲执行scan--->doScan方法，
public Set<BeanDefinitionHolder> doScan(String... basePackages) { Set<BeanDefinitionHolder> beanDefinitions = super.doScan(basePackages); for (BeanDefinitionHolder holder : beanDefinitions) { GenericBeanDefinition definition = (GenericBeanDefinition) holder.getBeanDefinition(); definition.getPropertyValues().add("mapperInterface", definition.getBeanClassName()); //实际就是将扫描到的接口包装成MapperFactoryBean的实现类 definition.setBeanClass(MapperFactoryBean.class); definition.getPropertyValues().add("addToConfig", this.addToConfig); boolean explicitFactoryUsed = false; //注入sqlSessionFactory对象，这个也很重要 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) { definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE); } } return beanDefinitions; }
这段代码其实主要就是从basePackage中扫描到相应的接口类，并且注册到spring中，并且定义此对象的FactoryBean为：MapperFactoryBean，将返回如下对象