MyBatis中SqlSessionFactory源码

SqlSessionFactory的作用

根据mapper配置文件解析出dao与具体jdbc操作、resultMap与实体类等的映射关系

1. SpringBoot整合MyBatis如何加载SqlSessionFactory

1.1 SpringBoot自动装配Spring.factories文件

Spring.factories文件中EnableAutoConfiguration对应的值MybatisAutoConfiguration

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.mybatis.spring.boot.autoconfigure.MybatisLanguageDriverAutoConfiguration,\
org.mybatis.spring.boot.autoconfigure.MybatisAutoConfiguration

1.2 读取yml配置文件中的mybatis配置

mybatis:
  mapper-locations: classpath:com/sunpy/demo/mapper/*Mapper.xml
  type-aliases-package: com.sunpy.demo.entity

MybatisAutoConfiguration中注入MybatisProperties配置类，实现：

@EnableConfigurationProperties这个注解的作用会将使用 @ConfigurationProperties的类进行了一次注入。

MybatisProperties类使用@ConfigurationProperties映射属性：
mybatis.mapper-locations 映射为 mapperLocations字段
mybatis.type-aliases-package 映射为 typeAliasesPackage字段

1.3 MybatisAutoConfiguration中SqlSessionFactory

实现的功能：
① 使用SqlSessionFactoryBean类，这个类实现了FactoryBean接口，通过getObject方法实例化SqlSessionFactory。说明SqlSessionFactoryBean类主要作用是实例化SqlSessionFactory。
② 设置datasource数据源。
③ 扫描映射的po类。
④ 扫描加载mapper中的xml文件。

@Bean
@ConditionalOnMissingBean
public SqlSessionFactory sqlSessionFactory(DataSource dataSource) throws Exception {
    // 设置数据源DataSource
    SqlSessionFactoryBean factory = new SqlSessionFactoryBean();
    factory.setDataSource(dataSource);
    factory.setVfs(SpringBootVFS.class);
    // 设置总配置文件，mybatis-config.xml
    if (StringUtils.hasText(this.properties.getConfigLocation())) {
      factory.setConfigLocation(this.resourceLoader.getResource(this.properties.getConfigLocation()));
    }
    applyConfiguration(factory);
    if (this.properties.getConfigurationProperties() != null) {
      factory.setConfigurationProperties(this.properties.getConfigurationProperties());
    }
    if (!ObjectUtils.isEmpty(this.interceptors)) {
      factory.setPlugins(this.interceptors);
    }
    if (this.databaseIdProvider != null) {
      factory.setDatabaseIdProvider(this.databaseIdProvider);
    }
    // 读取MybatisProperties中属性值，设置mybatis自动扫描到自定义的POJO
    if (StringUtils.hasLength(this.properties.getTypeAliasesPackage())) {
      factory.setTypeAliasesPackage(this.properties.getTypeAliasesPackage());
    }
    if (this.properties.getTypeAliasesSuperType() != null) {
      factory.setTypeAliasesSuperType(this.properties.getTypeAliasesSuperType());
    }
    if (StringUtils.hasLength(this.properties.getTypeHandlersPackage())) {
      factory.setTypeHandlersPackage(this.properties.getTypeHandlersPackage());
    }
    if (!ObjectUtils.isEmpty(this.typeHandlers)) {
      factory.setTypeHandlers(this.typeHandlers);
    }
    // 读取MybatisProperties中属性值，设置mapper-locations，扫描mapper的xml文件
    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);
    }
    // 创建SqlSessionFactory对象
    return factory.getObject();
}

1.4 注册SqlSessionFactory类到spring的逻辑

自动装配的逻辑中使用ConfigurationClassPostProcessor这个处理@Configuration注解的后置处理器，使用registerBeanDefinition方法，将当前的SqlSessionFactory类放入beanDefinitionMap中。

2. 细看SqlSessionFactoryBean实例化SqlSessionFactory

2.1 调用getObject方法实例化SqlSessionFactory

@Override
public SqlSessionFactory getObject() throws Exception {
    if (this.sqlSessionFactory == null) {
      afterPropertiesSet();
    }
 
    return this.sqlSessionFactory;
}
 
@Override
public void afterPropertiesSet() throws Exception {
    notNull(dataSource, "Property 'dataSource' is required");
    notNull(sqlSessionFactoryBuilder, "Property 'sqlSessionFactoryBuilder' is required");
    state((configuration == null && configLocation == null) || !(configuration != null && configLocation != null),
        "Property 'configuration' and 'configLocation' can not specified with together");
 
    this.sqlSessionFactory = buildSqlSessionFactory();
}

2.2 核心实现，委派给buildSqlSessionFactory()方法，构建SqlSessionFactory对象

  • 解析this.typeAliasesPackage，扫描到自定义的POJO，存放到this.typeAliases
  • 遍历mapper-locations，扫描mapper的所有xml文件，解析xml文件
protected SqlSessionFactory buildSqlSessionFactory() throws Exception {
 
    final Configuration targetConfiguration;
 
    XMLConfigBuilder xmlConfigBuilder = null;
    if (this.configuration != null) {
      targetConfiguration = this.configuration;
      if (targetConfiguration.getVariables() == null) {
        targetConfiguration.setVariables(this.configurationProperties);
      } else if (this.configurationProperties != null) {
        targetConfiguration.getVariables().putAll(this.configurationProperties);
      }
    } else if (this.configLocation != null) {
      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);
    }
 
    Optional.ofNullable(this.objectFactory).ifPresent(targetConfiguration::setObjectFactory);
    Optional.ofNullable(this.objectWrapperFactory).ifPresent(targetConfiguration::setObjectWrapperFactory);
    Optional.ofNullable(this.vfs).ifPresent(targetConfiguration::setVfsImpl);
    // 扫描到自定义的POJO，存放到this.typeAliases
    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);
    }
 
    if (!isEmpty(this.typeAliases)) {
      Stream.of(this.typeAliases).forEach(typeAlias -> {
        targetConfiguration.getTypeAliasRegistry().registerAlias(typeAlias);
        LOGGER.debug(() -> "Registered type alias: '" + typeAlias + "'");
      });
    }
 
    if (!isEmpty(this.plugins)) {
      Stream.of(this.plugins).forEach(plugin -> {
        targetConfiguration.addInterceptor(plugin);
        LOGGER.debug(() -> "Registered plugin: '" + plugin + "'");
      });
    }
 
    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 + "'");
      });
    }
 
    targetConfiguration.setDefaultEnumTypeHandler(defaultEnumTypeHandler);
 
    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));
    // 遍历mapper-locations，扫描mapper的所有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 {
        for (Resource mapperLocation : this.mapperLocations) {
          if (mapperLocation == null) {
            continue;
          }
          try {
            XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(mapperLocation.getInputStream(),
                targetConfiguration, mapperLocation.toString(), targetConfiguration.getSqlFragments());
            // 解析mapper的xml文件
            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.");
    }
 
    return this.sqlSessionFactoryBuilder.build(targetConfiguration);
}

3. 细看this.typeAliasesPackage指定的扫描po类加载存放到this.typeAliases

scanClasses(this.typeAliasesPackage, this.typeAliasesSuperType).stream()
          .filter(clazz -> !clazz.isAnonymousClass()).filter(clazz -> !clazz.isInterface())
          .filter(clazz -> !clazz.isMemberClass()).forEach(targetConfiguration.getTypeAliasRegistry()::registerAlias);
  • scanClasses实现
// 扫描指定packagePatterns路径下的类
private Set<Class<?>> scanClasses(String packagePatterns, Class<?> assignableType) throws IOException {
    Set<Class<?>> classes = new HashSet<>();
    // 根据指定的标记将字符串转换为字符串数组
    String[] packagePatternArray = tokenizeToStringArray(packagePatterns,
        ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
    for (String packagePattern : packagePatternArray) {
    // 加载拼接的指定路径下的所有类
      Resource[] resources = RESOURCE_PATTERN_RESOLVER.getResources(ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX
          + ClassUtils.convertClassNameToResourcePath(packagePattern) + "/**/*.class");
      for (Resource resource : resources) {
        try {
          ClassMetadata classMetadata = METADATA_READER_FACTORY.getMetadataReader(resource).getClassMetadata();
          Class<?> clazz = Resources.classForName(classMetadata.getClassName());
          // 搜集加载的类
          if (assignableType == null || assignableType.isAssignableFrom(clazz)) {
            classes.add(clazz);
          }
        } catch (Throwable e) {
          LOGGER.warn(() -> "Cannot load the '" + resource + "'. Cause by " + e.toString());
        }
      }
    }
    return classes;
}

4. 细看遍历mapper-locations，扫描mapper的所有xml文件，解析xml文件

for (Resource mapperLocation : this.mapperLocations) {
    if (mapperLocation == null) {
        continue;
    }
    try {
        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 + "'");
}

技术收获

    1. 根据指定的标记将字符串转换为字符串数组
      String[] packagePatternArray = tokenizeToStringArray(packagePatterns,
      ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
    1. 加载指定路径下的所有类
      Resource[] resources = RESOURCE_PATTERN_RESOLVER.getResources(ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX
  • ClassUtils.convertClassNameToResourcePath(packagePattern) + "//.class");*
    1. 解析加载xml文件
      xmlMapperBuilder.parse();
最后编辑于 ：
©著作权归作者所有,转载或内容合作请联系作者
平台声明：文章内容（如有图片或视频亦包括在内）由作者上传并发布，文章内容仅代表作者本人观点，简书系信息发布平台，仅提供信息存储服务。