Mybatis-SpringBoot源码解析之一：SqlSessionFactory加载流程

Mybatis-SpringBoot源码解析之一：SqlSessionFactory加载流程

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1、入口MybatisAutoConfiguration自动配置类

Mybatis同样通过自动配置的方式进行作为入口，将自动配置类本身以及内部的@Bean加载到beanDefinitionMap中，在后续创建单例的bean进行具体的解析创建真正的对象。

所以这儿会将MybatisAutoConfiguration、以及内部的SqlSessionFactory、SqlSessionTemplate封装成BeanDefinition放到beanDefinitionMap中。

MybatisAutoConfiguration重要代码如下所示：

public class MybatisAutoConfiguration implements InitializingBean {
    1、构造方法
        public MybatisAutoConfiguration(MybatisProperties properties, ObjectProvider<Interceptor[]> interceptorsProvider,ObjectProvider<TypeHandler[]> typeHandlersProvider, ObjectProvider<LanguageDriver[]> languageDriversProvider,ResourceLoader resourceLoader, ObjectProvider<DatabaseIdProvider> databaseIdProvider,ObjectProvider<List<ConfigurationCustomizer>> configurationCustomizersProvider) {
        2、MybatisProperties属性，也就是读取配置文件的属性
           类上面用到的@EnableConfigurationProperties(MybatisProperties.class)进行读取
        this.properties = properties;
        3、如果配置了的话获取拦截器
        this.interceptors = interceptorsProvider.getIfAvailable();
        4、获取类型处理器
        this.typeHandlers = typeHandlersProvider.getIfAvailable();
        this.languageDrivers = languageDriversProvider.getIfAvailable();
        this.resourceLoader = resourceLoader;
        this.databaseIdProvider = databaseIdProvider.getIfAvailable();
        this.configurationCustomizers = configurationCustomizersProvider.getIfAvailable();
    }
    
  @Bean
  @ConditionalOnMissingBean
  public SqlSessionFactory sqlSessionFactory(DataSource dataSource) throws Exception {
     ······省略
  }
  @Bean
  @ConditionalOnMissingBean
  public SqlSessionTemplate sqlSessionTemplate(SqlSessionFactory sqlSessionFactory) {
	······省略
  }
    
}

2、SqlSessionFactory流程sqlSessionFactory方法

@Bean
@ConditionalOnMissingBean
public SqlSessionFactory sqlSessionFactory(DataSource dataSource) throws Exception {
    1、 创建一个新的sql会话工厂
    SqlSessionFactoryBean factory = new SqlSessionFactoryBean();
    factory.setDataSource(dataSource);
    factory.setVfs(SpringBootVFS.class);
    2、获取Configuration 对象，Configuration 这个对象非常重要，贯穿了整个mybatis的流程
    if (StringUtils.hasText(this.properties.getConfigLocation())) {
        factory.setConfigLocation(this.resourceLoader.getResource(this.properties.getConfigLocation()));
    }
    2.1、在配置文件中获取 Configuration 对象 如果 获取不到 创建一个新的 Configuration 对象 （设置常用别名）
    applyConfiguration(factory);
    3、获取配置文件中configurationProperties属性
    if (this.properties.getConfigurationProperties() != null) {
        factory.setConfigurationProperties(this.properties.getConfigurationProperties());
    }
    4、如果当前拦截器不为空，将拦截器写入工厂中
    if (!ObjectUtils.isEmpty(this.interceptors)) {
        factory.setPlugins(this.interceptors);
    }
    if (this.databaseIdProvider != null) {
        factory.setDatabaseIdProvider(this.databaseIdProvider);
    }
    5、配置文件中获取的实体类包名
    if (StringUtils.hasLength(this.properties.getTypeAliasesPackage())) {
        factory.setTypeAliasesPackage(this.properties.getTypeAliasesPackage());
    }
    6、配置文件中获取的实体类型
    if (this.properties.getTypeAliasesSuperType() != null) {
        factory.setTypeAliasesSuperType(this.properties.getTypeAliasesSuperType());
    }
    7、配置文件中类型处理器包
    if (StringUtils.hasLength(this.properties.getTypeHandlersPackage())) {
        factory.setTypeHandlersPackage(this.properties.getTypeHandlersPackage());
    }
    8、设置类型处理器
    if (!ObjectUtils.isEmpty(this.typeHandlers)) {
        factory.setTypeHandlers(this.typeHandlers);
    }
    9、获取所有的mapper.xml文件设置到数组中
    if (!ObjectUtils.isEmpty(this.properties.resolveMapperLocations())) {
        factory.setMapperLocations(this.properties.resolveMapperLocations());
    }
    Set<String> factoryPropertyNames = Stream
        .of(new BeanWrapperImpl(SqlSessionFactoryBean.class).getPropertyDescriptors()).map(PropertyDescriptor::getName)
        .collect(Collectors.toSet());
    Class<? extends LanguageDriver> defaultLanguageDriver = this.properties.getDefaultScriptingLanguageDriver();
    if (factoryPropertyNames.contains("scriptingLanguageDrivers") && !ObjectUtils.isEmpty(this.languageDrivers)) {
        // Need to mybatis-spring 2.0.2+
        factory.setScriptingLanguageDrivers(this.languageDrivers);
        if (defaultLanguageDriver == null && this.languageDrivers.length == 1) {
            defaultLanguageDriver = this.languageDrivers[0].getClass();
        }
    }
    if (factoryPropertyNames.contains("defaultScriptingLanguageDriver")) {
        // Need to mybatis-spring 2.0.2+
        factory.setDefaultScriptingLanguageDriver(defaultLanguageDriver);
    }
	10、最终调用
    return factory.getObject();
}

流程较长，但是还是比较简单，就是设置一系列属性到工厂中，比较常见的就是mapperLocations以及typeAliasesPackage分别是mapper.xml资源以及实体包，最后调用getObject方法获取最终的sqlSessionFactory对象，
这儿可以先提前说一下最终返回的是DefaultSqlSessionFactory，有一个比较重要的属性是Configuration，后续会将所有的参数属性注入到该类中去。

3、getObject方法

  @Override
  public SqlSessionFactory getObject() throws Exception {
    if (this.sqlSessionFactory == null) {
      1、这个方法应该比较眼熟，spring初始化的方法，在这儿主动调用了。
      afterPropertiesSet();
    }

    return this.sqlSessionFactory;
  }

  @Override
  public void afterPropertiesSet() throws Exception {
      前面就是一堆校验，省略了只看重点
    1、构建sqlSessionFactory
    this.sqlSessionFactory = buildSqlSessionFactory();
  }

4、buildSqlSessionFactory构建工厂

protected SqlSessionFactory buildSqlSessionFactory() throws Exception {

    final Configuration targetConfiguration;

    XMLConfigBuilder xmlConfigBuilder = null;
    1、因为前面已经创建这儿configuration不为null
    if (this.configuration != null) {
      targetConfiguration = this.configuration;
      if (targetConfiguration.getVariables() == null) {
        1.1、设置配置文件中的variables属性是一个Map
        targetConfiguration.setVariables(this.configurationProperties);
      } else if (this.configurationProperties != null) {
        targetConfiguration.getVariables().putAll(this.configurationProperties);
      }
    } else if (this.configLocation != null) {
      1.2、根据本地的configLocation创建targetConfiguration
      xmlConfigBuilder = new XMLConfigBuilder(this.configLocation.getInputStream(), null, this.configurationProperties);
      targetConfiguration = xmlConfigBuilder.getConfiguration();
    } else {
      LOGGER.debug(
          () -> "Property 'configuration' or 'configLocation' not specified, using default MyBatis Configuration");
      targetConfiguration = new Configuration();
      Optional.ofNullable(this.configurationProperties).ifPresent(targetConfiguration::setVariables);
    }
	2、到这儿肯定会得到一个Configuration对象，后续Configuration发挥着巨大最作用。
    Optional.ofNullable(this.objectFactory).ifPresent(targetConfiguration::setObjectFactory);
    Optional.ofNullable(this.objectWrapperFactory).ifPresent(targetConfiguration::setObjectWrapperFactory);
    Optional.ofNullable(this.vfs).ifPresent(targetConfiguration::setVfsImpl);
	3、获取实体包，将实体包下面的实体设置到typeAliasRegistry属性上
    if (hasLength(this.typeAliasesPackage)) {
      scanClasses(this.typeAliasesPackage, this.typeAliasesSuperType).stream()
          .filter(clazz -> !clazz.isAnonymousClass()).filter(clazz -> !clazz.isInterface())
          .filter(clazz -> !clazz.isMemberClass()).forEach(targetConfiguration.getTypeAliasRegistry()::registerAlias);
    }
	3.1、同上，也是将实体设置到typeAliasRegistry属性上
    if (!isEmpty(this.typeAliases)) {
      Stream.of(this.typeAliases).forEach(typeAlias -> {
        targetConfiguration.getTypeAliasRegistry().registerAlias(typeAlias);
        LOGGER.debug(() -> "Registered type alias: '" + typeAlias + "'");
      });
    }
	4、设置插件
    if (!isEmpty(this.plugins)) {
      Stream.of(this.plugins).forEach(plugin -> {
        targetConfiguration.addInterceptor(plugin);
        LOGGER.debug(() -> "Registered plugin: '" + plugin + "'");
      });
    }
	5、设置类型处理器，其实就是java类型与数据库类型的对应，mybatis默认会设置很多
    if (hasLength(this.typeHandlersPackage)) {
      scanClasses(this.typeHandlersPackage, TypeHandler.class).stream().filter(clazz -> !clazz.isAnonymousClass())
          .filter(clazz -> !clazz.isInterface()).filter(clazz -> !Modifier.isAbstract(clazz.getModifiers()))
          .forEach(targetConfiguration.getTypeHandlerRegistry()::register);
    }

    if (!isEmpty(this.typeHandlers)) {
      Stream.of(this.typeHandlers).forEach(typeHandler -> {
        targetConfiguration.getTypeHandlerRegistry().register(typeHandler);
        LOGGER.debug(() -> "Registered type handler: '" + typeHandler + "'");
      });
    }

    if (!isEmpty(this.scriptingLanguageDrivers)) {
      Stream.of(this.scriptingLanguageDrivers).forEach(languageDriver -> {
        targetConfiguration.getLanguageRegistry().register(languageDriver);
        LOGGER.debug(() -> "Registered scripting language driver: '" + languageDriver + "'");
      });
    }
    Optional.ofNullable(this.defaultScriptingLanguageDriver)
        .ifPresent(targetConfiguration::setDefaultScriptingLanguage);

    if (this.databaseIdProvider != null) {// fix #64 set databaseId before parse mapper xmls
      try {
        targetConfiguration.setDatabaseId(this.databaseIdProvider.getDatabaseId(this.dataSource));
      } catch (SQLException e) {
        throw new NestedIOException("Failed getting a databaseId", e);
      }
    }

    Optional.ofNullable(this.cache).ifPresent(targetConfiguration::addCache);

    if (xmlConfigBuilder != null) {
      try {
        xmlConfigBuilder.parse();
        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();
      }
    }

    targetConfiguration.setEnvironment(new Environment(this.environment,
        this.transactionFactory == null ? new SpringManagedTransactionFactory() : this.transactionFactory,
        this.dataSource));
	6、重点：在这儿解析所有的mapper.xml文件
    if (this.mapperLocations != null) {
      if (this.mapperLocations.length == 0) {
        LOGGER.warn(() -> "Property 'mapperLocations' was specified but matching resources are not found.");
      } else {
          6.1、遍历mapper.xml文件进行解析
        for (Resource mapperLocation : this.mapperLocations) {
          if (mapperLocation == null) {
            continue;
          }
          try {
             6.2、创建xml的构造器
            XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(mapperLocation.getInputStream(),
                targetConfiguration, mapperLocation.toString(), targetConfiguration.getSqlFragments());
            xmlMapperBuilder.parse();
          } catch (Exception e) {
            throw new NestedIOException("Failed to parse mapping resource: '" + mapperLocation + "'", e);
          } finally {
            ErrorContext.instance().reset();
          }
          LOGGER.debug(() -> "Parsed mapper file: '" + mapperLocation + "'");
        }
      }
    } else {
      LOGGER.debug(() -> "Property 'mapperLocations' was not specified.");
    }
	7、构建DefaultSqlSessionFactory工厂，将Configuration属性封装进去
    return this.sqlSessionFactoryBuilder.build(targetConfiguration);
  }

设置一系列属性到Configuration中，后续会将该配置类注入到sqlSessioin工厂中。

这儿比较重要的就是解析所有的mapper.xml。

5、parse解析

  public void parse() {
    if (!configuration.isResourceLoaded(resource)) {
      1、解析mapper标签以及内部的标签
      configurationElement(parser.evalNode("/mapper"));
      configuration.addLoadedResource(resource);
      2、构建mapper与dao的关系
      bindMapperForNamespace();
    }
	3、下面就是对上述解析失败的再次进行尝试解析
    parsePendingResultMaps();
    parsePendingCacheRefs();
    parsePendingStatements();
  }

1、解析mapper标签以及内部的标签，见 第6章，这儿得到一个重要的对象MappedStatement，xml的sql标签被解析封装成该对象。

2、构建mapper与dao的关系

6、configurationElement解析

  private void configurationElement(XNode context) {
    try {
      1、获取当前mapper.xml的namespace属性也就是对应的dao
      String namespace = context.getStringAttribute("namespace");
      if (namespace == null || namespace.equals("")) {
        throw new BuilderException("Mapper's namespace cannot be empty");
      }
      builderAssistant.setCurrentNamespace(namespace);
      2、解析cache-ref标签
      cacheRefElement(context.evalNode("cache-ref"));
      3、解析cache标签
      cacheElement(context.evalNode("cache"));
      4、解析parameterMap标签
      parameterMapElement(context.evalNodes("/mapper/parameterMap"));
      5、解析resultMap标签
      resultMapElements(context.evalNodes("/mapper/resultMap"));
      6、解析sql标签
      sqlElement(context.evalNodes("/mapper/sql"));
      7、解析定义的sql语句
      buildStatementFromContext(context.evalNodes("select|insert|update|delete"));
    } catch (Exception e) {
      throw new BuilderException("Error parsing Mapper XML. The XML location is '" + resource + "'. Cause: " + e, e);
    }
  }

注意一下7、解析定义的sql语句，在这儿会对select、update等标签进行解析

7、buildStatementFromContext

1、解析所有的select、update、delete、insert标签
private void buildStatementFromContext(List<XNode> list) {
    if (configuration.getDatabaseId() != null) {
      buildStatementFromContext(list, configuration.getDatabaseId());
    }
    buildStatementFromContext(list, null);
  }

  private void buildStatementFromContext(List<XNode> list, String requiredDatabaseId) {
    2、遍历标签
    for (XNode context : list) {
      final XMLStatementBuilder statementParser = new XMLStatementBuilder(configuration, builderAssistant, context, requiredDatabaseId);
      try {
        3、真正的解析的方法
        statementParser.parseStatementNode();
      } catch (IncompleteElementException e) {
        configuration.addIncompleteStatement(statementParser);
      }
    }
  }

8、parseStatementNode解析sql语句

public void parseStatementNode() {
  String id = context.getStringAttribute("id");
  String databaseId = context.getStringAttribute("databaseId");

  if (!databaseIdMatchesCurrent(id, databaseId, this.requiredDatabaseId)) {
    return;
  }

  String nodeName = context.getNode().getNodeName();
  SqlCommandType sqlCommandType = SqlCommandType.valueOf(nodeName.toUpperCase(Locale.ENGLISH));
  boolean isSelect = sqlCommandType == SqlCommandType.SELECT;
  boolean flushCache = context.getBooleanAttribute("flushCache", !isSelect);
  boolean useCache = context.getBooleanAttribute("useCache", isSelect);
  boolean resultOrdered = context.getBooleanAttribute("resultOrdered", false);

  // Include Fragments before parsing
  XMLIncludeTransformer includeParser = new XMLIncludeTransformer(configuration, builderAssistant);
  includeParser.applyIncludes(context.getNode());

  String parameterType = context.getStringAttribute("parameterType");
  Class<?> parameterTypeClass = resolveClass(parameterType);

  String lang = context.getStringAttribute("lang");
  LanguageDriver langDriver = getLanguageDriver(lang);

  // Parse selectKey after includes and remove them.
  processSelectKeyNodes(id, parameterTypeClass, langDriver);

  // Parse the SQL (pre:  and  were parsed and removed)
  KeyGenerator keyGenerator;
  String keyStatementId = id + SelectKeyGenerator.SELECT_KEY_SUFFIX;
  keyStatementId = builderAssistant.applyCurrentNamespace(keyStatementId, true);
  if (configuration.hasKeyGenerator(keyStatementId)) {
    keyGenerator = configuration.getKeyGenerator(keyStatementId);
  } else {
    keyGenerator = context.getBooleanAttribute("useGeneratedKeys",
        configuration.isUseGeneratedKeys() && SqlCommandType.INSERT.equals(sqlCommandType))
        ? Jdbc3KeyGenerator.INSTANCE : NoKeyGenerator.INSTANCE;
  }

  SqlSource sqlSource = langDriver.createSqlSource(configuration, context, parameterTypeClass);
  StatementType statementType = StatementType.valueOf(context.getStringAttribute("statementType", StatementType.PREPARED.toString()));
  Integer fetchSize = context.getIntAttribute("fetchSize");
  Integer timeout = context.getIntAttribute("timeout");
  String parameterMap = context.getStringAttribute("parameterMap");
  String resultType = context.getStringAttribute("resultType");
  Class<?> resultTypeClass = resolveClass(resultType);
  String resultMap = context.getStringAttribute("resultMap");
  String resultSetType = context.getStringAttribute("resultSetType");
  ResultSetType resultSetTypeEnum = resolveResultSetType(resultSetType);
  if (resultSetTypeEnum == null) {
    resultSetTypeEnum = configuration.getDefaultResultSetType();
  }
  String keyProperty = context.getStringAttribute("keyProperty");
  String keyColumn = context.getStringAttribute("keyColumn");
  String resultSets = context.getStringAttribute("resultSets");

  builderAssistant.addMappedStatement(id, sqlSource, statementType, sqlCommandType,
      fetchSize, timeout, parameterMap, parameterTypeClass, resultMap, resultTypeClass,
      resultSetTypeEnum, flushCache, useCache, resultOrdered,
      keyGenerator, keyProperty, keyColumn, databaseId, langDriver, resultSets);
}

这儿就贴出来了，就不细讲了，就是解析标签上的所有的属性，然后封装成MappedStatement对象最终放到配置类Configuration的mappedStatements属性上。

这儿为什么一下保存了两条，说实话我也没看懂。明明只put了一次，不过都是指向一个MappedStatement。

回到代码块6进行进入到 2 。

9、bindMapperForNamespace构建dao与mapper的映射器

private void bindMapperForNamespace() {
  1、获取namespace
  String namespace = builderAssistant.getCurrentNamespace();
  if (namespace != null) {
    Class<?> boundType = null;
    try {
      2、反射出namespace类型
      boundType = Resources.classForName(namespace);
    } catch (ClassNotFoundException e) {
      //ignore, bound type is not required
    }
    if (boundType != null) {
      if (!configuration.hasMapper(boundType)) {
        // Spring may not know the real resource name so we set a flag
        // to prevent loading again this resource from the mapper interface
        // look at MapperAnnotationBuilder#loadXmlResource
        configuration.addLoadedResource("namespace:" + namespace);
        3、放入到mapperRegistry的knownMappers属性上。
        configuration.addMapper(boundType);
      }
    }
  }
}

3、这儿会将type进一步封装成MapperProxyFactory代理。

10、addMapper

public <T> void addMapper(Class<T> type) {
  if (type.isInterface()) {
    if (hasMapper(type)) {
      throw new BindingException("Type " + type + " is already known to the MapperRegistry.");
    }
    boolean loadCompleted = false;
    try {
      1、将MapperProxyFactory放入到knownMappers中
      knownMappers.put(type, new MapperProxyFactory<>(type));
      // It's important that the type is added before the parser is run
      // otherwise the binding may automatically be attempted by the
      // mapper parser. If the type is already known, it won't try.
      2、对使用注解的解析，如果该dao使用了的话。
      MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type);
      parser.parse();
      loadCompleted = true;
    } finally {
      if (!loadCompleted) {
        knownMappers.remove(type);
      }
    }
  }
}

将dao封装成MapperProxyFactory然后放到knownMappers属性中。

11 、总结

回想一下，SqlSessionFactoryBean干了哪些事：

• 处理所有的属性构建Configuration
• 解析mapper.xml内的各种标签，比较重要的就是将 mapper 文件中的每个 SQL 封装成 MappedStatement，放到 mappedStatements 缓存中，key 为 id，例如：com.xxx.open.mapper.UserPOMapper.queryByPrimaryKey，value 为 MappedStatement。
• 解析mapper.xml文件中对应的namespace，也就是对应的dao，将该类封装到mapperRegistry的knownMappers 缓存中，key为dao对应的Class，value为MapperProxyFactory。
• 最后将Configuration封装到DefaultSqlSessionFactory了上，得到SqlSessionFactory对象。