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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 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);        }      }    }  }

 

MyBatis 与 Spring 是如何结合在一起工作的——mybatis-spring(version:1.2.2)