Mybatis工作机制源码分析—初始化

       本文以Spring集成Mybatis的形式，在启动工程过程中，Spring容器会实例化SqlSessionFactoryBean，来讲解Mybatis是如何进行初始化工作。

Spring配置文件applicationContext.xml

<?xml version="1.0" encoding="UTF-8"?>  <beans xmlns="http://www.springframework.org/schema/beans"     xmlns:aop="http://www.springframework.org/schema/aop"   xmlns:tx="http://www.springframework.org/schema/tx"     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"   xmlns:context="http://www.springframework.org/schema/context"     xmlns:p="http://www.springframework.org/schema/p"     xsi:schemaLocation="          http://www.springframework.org/schema/beans           http://www.springframework.org/schema/beans/spring-beans-3.0.xsd           http://www.springframework.org/schema/tx           http://www.springframework.org/schema/tx/spring-tx-3.0.xsd           http://www.springframework.org/schema/context           http://www.springframework.org/schema/context/spring-context-3.0.xsd           http://www.springframework.org/schema/aop           http://www.springframework.org/schema/aop/spring-aop-3.0.xsd           http://www.springframework.org/schema/jdbc            http://www.springframework.org/schema/jdbc/spring-jdbc-3.0.xsd ">           <context:property-placeholder location="classpath:META-INF/dbproperties/*.properties" /><!-- 扫描注解文件  --><context:component-scan base-package="org.test" /><!-- 配置数据源 -->    <bean id="dataSource" class="org.apache.commons.dbcp2.BasicDataSource">    <property name="driverClassName" value="${db.driver}"></property> <property name="url" value="${db.url}" />        <property name="username" value="${db.userName}" />        <property name="password" value="${db.password}" />    <property name="maxTotal" value="10"/>     <property name="initialSize" value="5"/>    <property name="defaultReadOnly" value="false"/>    </bean><bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean"><property name="configLocation" value="classpath:META-INF/mybatis/config/mybatis-config.xml"></property><property name="dataSource" ref="dataSource" /><property name="mapperLocations" value="${sqlMapperLocations}" /></bean>  <!-- 配置sqlSessionTemplate -->     <bean id="sqlSessionTemplate" class="org.mybatis.spring.SqlSessionTemplate">          <constructor-arg index="0" ref="sqlSessionFactory" />      </bean><!-- 事务管理 --><bean id="transactionManager"class="org.springframework.jdbc.datasource.DataSourceTransactionManager"><property name="dataSource" ref="dataSource" /></bean><!-- 事务注解支持 --><tx:annotation-driven transaction-manager="transactionManager" /></beans>

SqlSessionFactoryBean与SqlSessionTemplate

       SqlSessionFactoryBean的主要工作为创建SqlSessionFactory实例；SqlSessionFactory再基于connection或DataSource来创建SqlSesion，SqlSesion可理解为一次sql会话，可进行sql语句形式的增删改查以及事务提交回滚等；SqlSessionTemplate则面向Mybatis对外的 DAO的使用者，通过以SqlSesion代理的形式，对外提供基于Spring事务管理的SqlSesion功能，SqlSessionTemplate是线程安全的，可多个DAO共用。

        SqlSessionFactoryBean部分源码：

/** SqlSessionFactoryBean.java */// 主要工作：创建SqlSessionFactory，在Spring容器中可通过依赖注入的形式被多个DAO共用public class SqlSessionFactoryBean implements FactoryBean<SqlSessionFactory>, InitializingBean, ApplicationListener<ApplicationEvent> {  private static final Log LOGGER = LogFactory.getLog(SqlSessionFactoryBean.class);  private Resource configLocation; // MyBatis config配置文件  private Resource[] mapperLocations; // MyBatis mapper配置文件  private DataSource dataSource; // 数据库源（一般带连接池）  private TransactionFactory transactionFactory;  private Properties configurationProperties;  private SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();  private SqlSessionFactory sqlSessionFactory; // sqlSession Factory，用来管理sqlSession    ...    // SqlSessionFactoryBean为FactoryBean，在Spring配置文件中直接获取，则获取sqlSessionFactory  public SqlSessionFactory getObject() throws Exception {    if (this.sqlSessionFactory == null) {      afterPropertiesSet();    }    return this.sqlSessionFactory;  }    // SqlSessionFactoryBean为InitializingBean，SqlSessionFactoryBean实例化过程中，主要初始化工作在afterPropertiesSet  public void afterPropertiesSet() throws Exception {    notNull(dataSource, "Property 'dataSource' is required");    notNull(sqlSessionFactoryBuilder, "Property 'sqlSessionFactoryBuilder' is required");    this.sqlSessionFactory = buildSqlSessionFactory();  }    // MyBatis初始化的核心工作，主要做两件事情：  // 1）解析Mybatis config、mapper配置文件；2）用解析结果configuration创建DefaultSqlSessionFactory实例  protected SqlSessionFactory buildSqlSessionFactory() throws IOException {    Configuration configuration;    XMLConfigBuilder xmlConfigBuilder = null;    if (this.configLocation != null) {      xmlConfigBuilder = new XMLConfigBuilder(this.configLocation.getInputStream(), null, this.configurationProperties);      configuration = xmlConfigBuilder.getConfiguration();    } else {      if (LOGGER.isDebugEnabled()) {        LOGGER.debug("Property 'configLocation' not specified, using default MyBatis Configuration");      }      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);        if (LOGGER.isDebugEnabled()) {          LOGGER.debug("Scanned package: '" + packageToScan + "' for aliases");        }      }    }    if (!isEmpty(this.typeAliases)) {      for (Class<?> typeAlias : this.typeAliases) {        configuration.getTypeAliasRegistry().registerAlias(typeAlias);        if (LOGGER.isDebugEnabled()) {          LOGGER.debug("Registered type alias: '" + typeAlias + "'");        }      }    }    if (!isEmpty(this.plugins)) {      for (Interceptor plugin : this.plugins) {        configuration.addInterceptor(plugin);        if (LOGGER.isDebugEnabled()) {          LOGGER.debug("Registered plugin: '" + plugin + "'");        }      }    }    if (hasLength(this.typeHandlersPackage)) {      String[] typeHandlersPackageArray = tokenizeToStringArray(this.typeHandlersPackage,          ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);      for (String packageToScan : typeHandlersPackageArray) {        configuration.getTypeHandlerRegistry().register(packageToScan);        if (LOGGER.isDebugEnabled()) {          LOGGER.debug("Scanned package: '" + packageToScan + "' for type handlers");        }      }    }    if (!isEmpty(this.typeHandlers)) {      for (TypeHandler<?> typeHandler : this.typeHandlers) {        configuration.getTypeHandlerRegistry().register(typeHandler);        if (LOGGER.isDebugEnabled()) {          LOGGER.debug("Registered type handler: '" + typeHandler + "'");        }      }    }    if (xmlConfigBuilder != null) {      try {        xmlConfigBuilder.parse();        if (LOGGER.isDebugEnabled()) {          LOGGER.debug("Parsed configuration file: '" + this.configLocation + "'");        }      } catch (Exception ex) {        throw new NestedIOException("Failed to parse config resource: " + this.configLocation, ex);      } finally {        ErrorContext.instance().reset();      }    }    if (this.transactionFactory == null) {      this.transactionFactory = new SpringManagedTransactionFactory();    }    configuration.setEnvironment(new Environment(this.environment, this.transactionFactory, this.dataSource));    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 {          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();        }        if (LOGGER.isDebugEnabled()) {          LOGGER.debug("Parsed mapper file: '" + mapperLocation + "'");        }      }    } else {      if (LOGGER.isDebugEnabled()) {        LOGGER.debug("Property 'mapperLocations' was not specified or no matching resources found");      }    }    return this.sqlSessionFactoryBuilder.build(configuration);  }    // SqlSessionFactoryBean为ApplicationListener，响应ApplicationEvent事件  public void onApplicationEvent(ApplicationEvent event) {    if (failFast && event instanceof ContextRefreshedEvent) {      // fail-fast -> check all statements are completed      this.sqlSessionFactory.getConfiguration().getMappedStatementNames();    }  }    ...}  

        SqlSessionFactory接口：

/** SqlSessionFactory.java */// SqlSessionFactory基于connection或DataSource来创建SqlSesionpublic interface SqlSessionFactory {  SqlSession openSession();  SqlSession openSession(boolean autoCommit);  SqlSession openSession(Connection connection);  SqlSession openSession(TransactionIsolationLevel level);  SqlSession openSession(ExecutorType execType);  SqlSession openSession(ExecutorType execType, boolean autoCommit);  SqlSession openSession(ExecutorType execType, TransactionIsolationLevel level);  SqlSession openSession(ExecutorType execType, Connection connection);  Configuration getConfiguration();}

       SqlSesion接口概览：

       SqlSessionTemplate部分源码：

/** SqlSessionTemplate.java */// SqlSessionTemplate以SqlSesion代理的形式，对外提供基于Spring事务管理的SqlSesion功能；// SqlSessionTemplate是线程安全的，可多个DAO共用public class SqlSessionTemplate implements SqlSession {  private final SqlSessionFactory sqlSessionFactory; // 借助sqlSessionFactory来创建SqlSessions  private final ExecutorType executorType;  private final SqlSession sqlSessionProxy; // 对外的sqlSession代理，对使用者是透明的  private final PersistenceExceptionTranslator exceptionTranslator;    ...    public SqlSessionTemplate(SqlSessionFactory sqlSessionFactory) {    this(sqlSessionFactory, sqlSessionFactory.getConfiguration().getDefaultExecutorType());  }    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;// JDK动态代理    this.sqlSessionProxy = (SqlSession) newProxyInstance(        SqlSessionFactory.class.getClassLoader(),        new Class[] { SqlSession.class },        new SqlSessionInterceptor());  }    private class SqlSessionInterceptor implements InvocationHandler {    @Override    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {      SqlSession sqlSession = getSqlSession(          SqlSessionTemplate.this.sqlSessionFactory,          SqlSessionTemplate.this.executorType,          SqlSessionTemplate.this.exceptionTranslator);      try {        Object result = method.invoke(sqlSession, args); // 代理方法调用，实际调用的是sqlSessionFactory创建的sqlSession        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);        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);          if (translated != null) {            unwrapped = translated;          }        }        throw unwrapped;      } finally {        if (sqlSession != null) {          closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory);        }      }    }  }  ...}

整体流程

         Mybatis初始化核心工作在SqlSessionFactoryBean的实例化，其为FactoryBean且实现InitializingBean接口：

public void afterPropertiesSet() throws Exception {    notNull(dataSource, "Property 'dataSource' is required");    notNull(sqlSessionFactoryBuilder, "Property 'sqlSessionFactoryBuilder' is required");    this.sqlSessionFactory = buildSqlSessionFactory();  }

buildSqlSessionFactory()则进行初始化工作。

时序图

相关类结构图

相关源码

/** SqlSessionFactoryBean.java */protected SqlSessionFactory buildSqlSessionFactory() throws IOException {Configuration configuration;XMLConfigBuilder xmlConfigBuilder = null;if (this.configLocation != null) {  // 构建xmlConfigBuilder，核心工作为构造XPathParser：完成Mybatis的配置文件inputStream到Document对象的转化；设置xpath sax解析工具  xmlConfigBuilder = new XMLConfigBuilder(this.configLocation.getInputStream(), null, this.configurationProperties);  // 解析结果configuration  configuration = xmlConfigBuilder.getConfiguration();} else {  if (LOGGER.isDebugEnabled()) {LOGGER.debug("Property 'configLocation' not specified, using default MyBatis Configuration");  }  configuration = new Configuration();  configuration.setVariables(this.configurationProperties);}// configuration设置SqlSessionFactoryBean依赖注入的objectFactory、objectWrapperFactory、typeAliasesPackage// typeAliases、plugins、typeHandlersPackage、typeHandlers实例到相应的属性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);if (LOGGER.isDebugEnabled()) {  LOGGER.debug("Scanned package: '" + packageToScan + "' for aliases");}  }}if (!isEmpty(this.typeAliases)) {  for (Class<?> typeAlias : this.typeAliases) {configuration.getTypeAliasRegistry().registerAlias(typeAlias);if (LOGGER.isDebugEnabled()) {  LOGGER.debug("Registered type alias: '" + typeAlias + "'");}  }}if (!isEmpty(this.plugins)) {  for (Interceptor plugin : this.plugins) {configuration.addInterceptor(plugin);if (LOGGER.isDebugEnabled()) {  LOGGER.debug("Registered plugin: '" + plugin + "'");}  }}if (hasLength(this.typeHandlersPackage)) {  String[] typeHandlersPackageArray = tokenizeToStringArray(this.typeHandlersPackage,  ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);  for (String packageToScan : typeHandlersPackageArray) {configuration.getTypeHandlerRegistry().register(packageToScan);if (LOGGER.isDebugEnabled()) {  LOGGER.debug("Scanned package: '" + packageToScan + "' for type handlers");}  }}if (!isEmpty(this.typeHandlers)) {  for (TypeHandler<?> typeHandler : this.typeHandlers) {configuration.getTypeHandlerRegistry().register(typeHandler);if (LOGGER.isDebugEnabled()) {  LOGGER.debug("Registered type handler: '" + typeHandler + "'");}  }}if (xmlConfigBuilder != null) {  try {// 解析MyBatis config配置文件xmlConfigBuilder.parse();if (LOGGER.isDebugEnabled()) {  LOGGER.debug("Parsed configuration file: '" + this.configLocation + "'");}  } catch (Exception ex) {throw new NestedIOException("Failed to parse config resource: " + this.configLocation, ex);  } finally {ErrorContext.instance().reset();  }}// configuration设置environment、databaseIdif (this.transactionFactory == null) {  // 采用Spring管理的TransactionFactory  this.transactionFactory = new SpringManagedTransactionFactory();}// 覆盖Mybatis config配置文件中配置的Environment，主要涉及SpringManagedTransactionFactoryconfiguration.setEnvironment(new Environment(this.environment, this.transactionFactory, this.dataSource));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 {  // 构造XMLMapperBuilder  XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(mapperLocation.getInputStream(),  configuration, mapperLocation.toString(), configuration.getSqlFragments());  // 解析MyBatis mapper配置文件  xmlMapperBuilder.parse();} catch (Exception e) {  throw new NestedIOException("Failed to parse mapping resource: '" + mapperLocation + "'", e);} finally {  ErrorContext.instance().reset();}if (LOGGER.isDebugEnabled()) {  LOGGER.debug("Parsed mapper file: '" + mapperLocation + "'");}  }} else {  if (LOGGER.isDebugEnabled()) {LOGGER.debug("Property 'mapperLocations' was not specified or no matching resources found");  }}// 返回DefaultSqlSessionFactoryreturn this.sqlSessionFactoryBuilder.build(configuration);}

详细流程

构造XMLConfigBuilder

/** XMLConfigBuilder.java */// XMLConfigBuilder构造器public XMLConfigBuilder(InputStream inputStream, String environment, Properties props) {// XMLMapperEntityResolver用于加载"org/apache/ibatis/builder/xml/mybatis-3-config.dtd"、// "org/apache/ibatis/builder/xml/mybatis-3-mapper.dtd"为InputSource，用于sax解析Mybatis的config、mapper配置文件// MyBatis采用dtd模式来解析其配置文件this(new XPathParser(inputStream, true, props, new XMLMapperEntityResolver()), environment, props);}private XMLConfigBuilder(XPathParser parser, String environment, Properties props) {super(new Configuration());ErrorContext.instance().resource("SQL Mapper Configuration");this.configuration.setVariables(props);this.parsed = false;this.environment = environment;this.parser = parser;}/** XPathParser.java */// XPathParser构造函数，完成Mybatis的配置文件inputStream到Document对象的转化public XPathParser(InputStream inputStream, boolean validation, Properties variables, EntityResolver entityResolver) {commonConstructor(validation, variables, entityResolver);this.document = createDocument(new InputSource(inputStream));}// 设置解析工具private void commonConstructor(boolean validation, Properties variables, EntityResolver entityResolver) {this.validation = validation;this.entityResolver = entityResolver;this.variables = variables;XPathFactory factory = XPathFactory.newInstance();// 借助javax.xml.xpath.XPath辅助XPathParser解析this.xpath = factory.newXPath();}// 将Mybatis的配置文件inputStream转化为Document对象private Document createDocument(InputSource inputSource) {// important: this must only be called AFTER common constructortry {  // 利用javax.xml.parsers.DocumentBuilderFactory来创建DocumentBuilder  DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();  factory.setValidating(validation);  factory.setNamespaceAware(false);  factory.setIgnoringComments(true);  factory.setIgnoringElementContentWhitespace(false);  factory.setCoalescing(false);  factory.setExpandEntityReferences(true);  DocumentBuilder builder = factory.newDocumentBuilder();  // 设置javax.xml.parsers.DocumentBuilder  builder.setEntityResolver(entityResolver);  builder.setErrorHandler(new ErrorHandler() {@Overridepublic void error(SAXParseException exception) throws SAXException {  throw exception;}@Overridepublic void fatalError(SAXParseException exception) throws SAXException {  throw exception;}@Overridepublic void warning(SAXParseException exception) throws SAXException {}  });  // inputSource解析为Document对象  return builder.parse(inputSource);} catch (Exception e) {  throw new BuilderException("Error creating document instance.  Cause: " + e, e);}}

Mybatis 配置文件sax解析

详见：Mybatis工作机制源码分析—初始化—sax解析

Mybatis config配置文件解析

详见：Mybatis工作机制源码分析—初始化—config配置文件解析

Mybatis mapper配置文件解析

详见：Mybatis工作机制源码分析—初始化—mapper配置文件解析