MyBatis 与 Spring 是如何结合在一起工作的——mybatis-spring（version：1.2.2）
在MyBatis-Spring的项目中，我们一般会为MyBatis配置两个配置文件 beans-mybatis.xml 和 mybatis-config.xml。
其中 beans-mybatis.xml 中配置的是MyBatis 和 Spring结合使用时委托给 spring 管理的 bean。
mybatis-config.xml 中是MyBatis 自身的配置。
例：beans-mybatis.xml
<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean" p:dataSource-ref="dataSource" p:configLocation="classpath:mybatis-config.xml" p:mapperLocations="classpath:mapper/**/*.xml" /> <bean id="transactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager"> <property name="dataSource" ref="dataSource" /> </bean> <tx:annotation-driven transaction-manager="transactionManager" /> <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer" p:basePackage="com.cn.kvn.usage.dao" />
mybatis-config.xml：
<configuration> <settings> <setting name="lazyLoadingEnabled" value="false" /> <!-- logback日志指定打印sql用 --> <setting name="logPrefix" value="dao." /> </settings> <typeAliases> <!-- 别名定义 --> </typeAliases> <!-- 插件 --> <plugins> <plugin interceptor="com.cn.kvn.framework.jdbc.mybatis.interceptor.PageInterceptor"> <property name="dialectClassName" value="com.cn.kvn.framework.jdbc.mybatis.interceptor.MySQLDialect" /> </plugin> </plugins> </configuration>
mybatis-spring的入口就在bean的定义那里（beans-mybatis.xml ）： SqlSessionFactoryBean 、MapperScannerConfigurer
#####1. SqlSessionFactoryBean
SqlSessionFactoryBean实现了 InitializingBean ，在 afterPropertiesSet() 中会对 mybatis的配置 p:configLocation="classpath:mybatis-config.xml" 、 p:mapperLocations="classpath:mapper/**/*.xml" 进行解析。
org.mybatis.spring.SqlSessionFactoryBean#buildSqlSessionFactory()：
protected SqlSessionFactory buildSqlSessionFactory() throws IOException { Configuration configuration; // MyBatis 的配置，存放 mybatis-config.xml 中的配置 XMLConfigBuilder xmlConfigBuilder = null; // mybatis-config.xml 的解析器，解析出来的内容放在 Configuration 中 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)) { // typeAlias : 类型别名，用于sqlmap中类型（parameterType、resultType）的配置 String[] typeAliasPackageArray = tokenizeToStringArray(this.typeAliasesPackage, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS); for (String packageToScan : typeAliasPackageArray) { configuration.getTypeAliasRegistry().registerAliases(packageToScan, typeAliasesSuperType == null ? Object.class : typeAliasesSuperType); // 注册 typeAliases } } if (!isEmpty(this.typeAliases)) { // typeAlias : 类型别名，用于sqlmap中类型（parameterType、resultType）的配置 for (Class<?> typeAlias : this.typeAliases) { configuration.getTypeAliasRegistry().registerAlias(typeAlias); // 注册 typeAliases } } if (!isEmpty(this.plugins)) { // plugins : mybatis 的插件，即 MyBatis 的拦截器和扩展点。可以针对Executor 、 StatementHandler 、 ResultSetHandler 和 PameterHandler 进行拦截扩展 for (Interceptor plugin : this.plugins) { configuration.addInterceptor(plugin); // 添加 MyBatis Interceptor } } if (hasLength(this.typeHandlersPackage)) { // typeHandler : 类型转换器，对java类型和sqlmap中的类型进行转换 String[] typeHandlersPackageArray = tokenizeToStringArray(this.typeHandlersPackage, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS); for (String packageToScan : typeHandlersPackageArray) { configuration.getTypeHandlerRegistry().register(packageToScan); // 注册 typeHandler } } if (!isEmpty(this.typeHandlers)) { // typeHandler : 类型转换器，对java类型和sqlmap中的类型进行转换 for (TypeHandler<?> typeHandler : this.typeHandlers) { configuration.getTypeHandlerRegistry().register(typeHandler); // 注册 typeHandler } } if (xmlConfigBuilder != null) { try { xmlConfigBuilder.parse(); // xmlConfigBuilder解析 mybatis-spring.xml 配置 } catch (Exception ex) { throw new NestedIOException("Failed to parse config resource: " + this.configLocation, ex); } finally { ErrorContext.instance().reset(); // 重置 ErrorContext } } if (this.transactionFactory == null) { this.transactionFactory = new SpringManagedTransactionFactory(); // 默认的 transactionFactory } 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)); // DatabaseId 用于对多数据库的支持 } 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 { XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(mapperLocation.getInputStream(), configuration, mapperLocation.toString(), configuration.getSqlFragments()); xmlMapperBuilder.parse(); // xmlMapperBuilder：解析 mapperLocation 中指定的 sqlmap 文件，即解析 sql 语句 } catch (Exception e) { throw new NestedIOException("Failed to parse mapping resource: '" + mapperLocation + "'", e); } finally { ErrorContext.instance().reset(); // 重置 ErrorContext } } } return this.sqlSessionFactoryBuilder.build(configuration); // 将 configuration 配置设置到 org.apache.ibatis.session.defaults.DefaultSqlSessionFactory 中 }
附：ErrorContext: 解析配置文件时，用于存储异常信息（ThreadLocal实现的）
跟配置解析相关的类：
XMLConfigBuilder ： 解析 mybatis-config.xml 中 MyBatis 自身的配置。
XmlMapperBuilder ： 解析 sqlmap 中的配置，包括 <resultMap> 和 sql 语句
ResultMapResolver ： 解析 sqlmap 中的 <resultMap> 节点
XMLStatementBuilder ： 解析 sql 语句（<insert>、<delete>、<update>、<select>）
举例：mybatis-config.xml 的解析是通过 XMLConfigBuilder 来完成的
mybatis-config.xml中能够配置的属性：（XMLConfigBuilder#parseConfiguration(XNode)）
private void parseConfiguration(XNode root) { try { propertiesElement(root.evalNode("properties")); //issue #117 read properties first typeAliasesElement(root.evalNode("typeAliases")); pluginElement(root.evalNode("plugins")); objectFactoryElement(root.evalNode("objectFactory")); objectWrapperFactoryElement(root.evalNode("objectWrapperFactory")); settingsElement(root.evalNode("settings")); environmentsElement(root.evalNode("environments")); // read it after objectFactory and objectWrapperFactory issue #631 databaseIdProviderElement(root.evalNode("databaseIdProvider")); typeHandlerElement(root.evalNode("typeHandlers")); mapperElement(root.evalNode("mappers")); } catch (Exception e) { throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e); } }
其中<settings>标签可以配置的属性如下：（XMLConfigBuilder#settingsElement(XNode)）
configuration.setAutoMappingBehavior(AutoMappingBehavior.valueOf(props.getProperty("autoMappingBehavior", "PARTIAL"))); configuration.setCacheEnabled(booleanValueOf(props.getProperty("cacheEnabled"), true)); configuration.setProxyFactory((ProxyFactory) createInstance(props.getProperty("proxyFactory"))); configuration.setLazyLoadingEnabled(booleanValueOf(props.getProperty("lazyLoadingEnabled"), false)); configuration.setAggressiveLazyLoading(booleanValueOf(props.getProperty("aggressiveLazyLoading"), true)); configuration.setMultipleResultSetsEnabled(booleanValueOf(props.getProperty("multipleResultSetsEnabled"), true)); configuration.setUseColumnLabel(booleanValueOf(props.getProperty("useColumnLabel"), true)); configuration.setUseGeneratedKeys(booleanValueOf(props.getProperty("useGeneratedKeys"), false)); configuration.setDefaultExecutorType(ExecutorType.valueOf(props.getProperty("defaultExecutorType", "SIMPLE"))); configuration.setDefaultStatementTimeout(integerValueOf(props.getProperty("defaultStatementTimeout"), null)); configuration.setMapUnderscoreToCamelCase(booleanValueOf(props.getProperty("mapUnderscoreToCamelCase"), false)); configuration.setSafeRowBoundsEnabled(booleanValueOf(props.getProperty("safeRowBoundsEnabled"), false)); configuration.setLocalCacheScope(LocalCacheScope.valueOf(props.getProperty("localCacheScope", "SESSION"))); configuration.setJdbcTypeForNull(JdbcType.valueOf(props.getProperty("jdbcTypeForNull", "OTHER"))); configuration.setLazyLoadTriggerMethods(stringSetValueOf(props.getProperty("lazyLoadTriggerMethods"), "equals,clone,hashCode,toString")); configuration.setSafeResultHandlerEnabled(booleanValueOf(props.getProperty("safeResultHandlerEnabled"), true)); configuration.setDefaultScriptingLanguage(resolveClass(props.getProperty("defaultScriptingLanguage"))); configuration.setCallSettersOnNulls(booleanValueOf(props.getProperty("callSettersOnNulls"), false)); configuration.setLogPrefix(props.getProperty("logPrefix")); configuration.setLogImpl(resolveClass(props.getProperty("logImpl"))); configuration.setConfigurationFactory(resolveClass(props.getProperty("configurationFactory")));
#####2. MapperScannerConfigurer
MapperScannerConfigurer 的作用是扫描 java 的 Dao 接口，来与 mapper 做映射关系
org.mybatis.spring.mapper.MapperScannerConfigurer#postProcessBeanDefinitionRegistry(BeanDefinitionRegistry)
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException { 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(); // java类型过滤器，排除一些不符合要求的 Dao scanner.scan(StringUtils.tokenizeToStringArray(this.basePackage, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS)); // 进行 Dao 扫描，扫描 basePackage 包下面的类 }
org.mybatis.spring.mapper.ClassPathMapperScanner#scan(String... basePackages)：
public Set<BeanDefinitionHolder> doScan(String... basePackages) { Set<BeanDefinitionHolder> beanDefinitions = super.doScan(basePackages); // 调用 ClassPathBeanDefinitionScanner#doScan()解析出bean for (BeanDefinitionHolder holder : beanDefinitions) { GenericBeanDefinition definition = (GenericBeanDefinition) holder.getBeanDefinition(); // the mapper interface is the original class of the bean // but, the actual class of the bean is MapperFactoryBean definition.getPropertyValues().add("mapperInterface", definition.getBeanClassName()); // mapperInterface 是 Dao 对应的 bean 的原始类型 definition.setBeanClass(MapperFactoryBean.class); // MapperFactoryBean 是 Dao 对应的 bean 的实际类型。也就是所有的 Dao 对应的 bean ，最后都是 MapperFactoryBean，通过 MapperFactoryBean 来做 Dao 的代理，将CRUD操作分发到具体的 sqlmap 中的 sql 去执行。 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)) { definition.getPropertyValues().add("sqlSessionTemplate", new RuntimeBeanReference(this.sqlSessionTemplateBeanName)); explicitFactoryUsed = true; } else if (this.sqlSessionTemplate != null) { definition.getPropertyValues().add("sqlSessionTemplate", this.sqlSessionTemplate); explicitFactoryUsed = true; } if (!explicitFactoryUsed) { definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE); // 让 MapperFactoryBean 可以通过 @Autowired 注解来进行注入。即注入 xxxDao } return beanDefinitions; }
#####3. MapperFactoryBean
MapperFactoryBean 继承了SqlSessionDaoSupport，默认使用了 org.mybatis.spring.SqlSessionTemplate 来操作CRUD方法。
org.mybatis.spring.SqlSessionTemplate 的构造方法：
public SqlSessionTemplate(SqlSessionFactory sqlSessionFactory, ExecutorType executorType, PersistenceExceptionTranslator exceptionTranslator) { notNull(sqlSessionFactory, "Property 'sqlSessionFactory' is required"); notNull(executorType, "Property 'executorType' is required"); this.sqlSessionFactory = sqlSessionFactory; this.executorType = executorType; this.exceptionTranslator = exceptionTranslator; // 默认使用 MyBatisExceptionTranslator ，对 SQL 异常进行友好转换 this.sqlSessionProxy = (SqlSession) newProxyInstance( SqlSessionFactory.class.getClassLoader(), new Class[] { SqlSession.class }, new SqlSessionInterceptor()); }
SqlSessionTemplate 又是通过 sqlSessionProxy 来操作CRUD方法的。
sqlSessionProxy 是JDK 动态代理，通过 SqlSessionInterceptor 来拦截 org.apache.ibatis.session.SqlSession 接口里面的 CRUD 操作。
org.mybatis.spring.SqlSessionTemplate.SqlSessionInterceptor：
/** * Proxy needed to route MyBatis method calls to the proper SqlSession got * from Spring's Transaction Manager * It also unwraps exceptions thrown by {@code Method#invoke(Object, Object...)} to * pass a {@code PersistenceException} to the {@code PersistenceExceptionTranslator}. */ private class SqlSessionInterceptor implements InvocationHandler { public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { SqlSession sqlSession = getSqlSession( SqlSessionTemplate.this.sqlSessionFactory, SqlSessionTemplate.this.executorType, SqlSessionTemplate.this.exceptionTranslator); // 从当前线程中获取一个 SqlSession ，如果没有，就创建一个新的 SqlSession。（org.apache.ibatis.session.defaults.DefaultSqlSessionFactory#openSession(ExecutorType execType)）。这样 spring 和 mybatis 就结合在一起了 try { Object result = method.invoke(sqlSession, args); // 执行 SqlSession 的方法（CRUD操作）。 if (!isSqlSessionTransactional(sqlSession, SqlSessionTemplate.this.sqlSessionFactory)) { // force commit even on non-dirty sessions because some databases require // a commit/rollback before calling close() sqlSession.commit(true); } return result; } catch (Throwable t) { Throwable unwrapped = unwrapThrowable(t); // 对 Method#invoke(Object, Object...) 的异常进行解封装 if (SqlSessionTemplate.this.exceptionTranslator != null && unwrapped instanceof PersistenceException) { // release the connection to avoid a deadlock if the translator is no loaded. See issue #22 closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory); sqlSession = null; Throwable translated = SqlSessionTemplate.this.exceptionTranslator.translateExceptionIfPossible((PersistenceException) unwrapped); // 对 SQL 异常进行友好转换 if (translated != null) { unwrapped = translated; } } throw unwrapped; } finally { if (sqlSession != null) { closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory); } } } }
至此，我们还有一个问题没有解决：我们在调用 xxDao 中的方法 xxMethod 时，mybatis-spring.jar 是如何找到 xxMethod 对应的配置文件 xxMapper.xml 中的 sql 语句的？
它是通过多个 JDK 动态代理，去拦截 mapperInterface（xxDao）中的方法来实现的。具体可以看下图：
通过上图，前面的疑问就迎刃而解了。^_^
附：MapperFactoryBean 中的 sqlSessionFactory 是如何注入的？
在 Spring 容器里面 IJobBeforehandRetryDao.java 对应的 beanName = "IJobBeforehandRetryDao"
相应的 RootBeanDefinition为：
Root bean: class [org.mybatis.spring.mapper.MapperFactoryBean]; scope=singleton; abstract=false; lazyInit=false; autowireMode=2; dependencyCheck=0; autowireCandidate=true; primary=false; factoryBeanName=null; factoryMethodName=null; initMethodName=null; destroyMethodName=null; defined in file [E:\gitWorkspace\dal-job\dal-job-core\target\classes\com\kvn\dal\core\dao\IJobBeforehandRetryDao.class]
IJobBeforehandRetryDao 对应的 bean 是一个 FactoryBean。Spring 对 FactoryBean 里面的属性有特殊处理。
AbstractAutowireCapableBeanFactory#autowireByType(String beanName, AbstractBeanDefinition mbd, BeanWrapper bw, MutablePropertyValues pvs)
MapperFactoryBean#setSqlSessionFactory(SqlSessionFactory sqlSessionFactory)会被调用。
这样，MapperFactoryBean 中的属性 sqlSession就会被赋值。 this.sqlSession = new SqlSessionTemplate(sqlSessionFactory);
