【MyBatis】Spring集成原理（一）：创建 SqlSessionFactory

迷南。 2022-12-28 12:36 197阅读 0赞

在[上一篇][Link 1]我们演示了 Spring 如何整合 MyBatis；那么问题来了，会话工厂 SqlSessionFactory 是什么时候创建的？为了解开其中奥秘，我们就从 Spring 集成时配置的 SqlSessionFactoryBean 源码看起…

**SqlSessionFactoryBean**

SqlSessionFactoryBean 从名字就能看出来它是用来创建工厂类的，继承关系如下：

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzkzNTkyNw_size_16_color_FFFFFF_t_70_pic_center]  
其中，InitializingBean 接口为 bean 提供了初始化方法的方式，它只包括 afterPropertiesSet() 方法，凡是继承该接口的类，在 bean 的属性值设置完的时候会自动执行该方法。

> PS：关于 InitializingBean 可以参考[这篇文章][Link 2]…

@Override
    public void afterPropertiesSet() throws Exception {
        
      // 检查标签属性dataSource，SqlSessionFactoryBuilder
      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");
        
      // 创建会话工厂 SqlSessionFactory
      this.sqlSessionFactory = buildSqlSessionFactory();
    }

另外，它还实现了 FactoryBean 接口，所以 getBean() 获取 SqlSessionFactory 实例的时候，实际上是调用 FactoryBean\#getObject() 方法。可以看到，它里面调用的也是 afterPropertiesSet() 方法。

> PS：关于 FactoryBean 可以参考[这篇文章][Link 3]…

@Override
    public SqlSessionFactory getObject() throws Exception {
        
      if (this.sqlSessionFactory == null) {
        
        afterPropertiesSet();
      }
    
      return this.sqlSessionFactory;
    }

**buildSqlSessionFactory()**

protected SqlSessionFactory buildSqlSessionFactory() throws IOException {
        
      // 定义了一个Configuration，叫做targetConfiguration。
      final Configuration targetConfiguration;
    
      XMLConfigBuilder xmlConfigBuilder = null;
      // 判断 Configuration 对象是否已经存在，也就是是否已经解析过。如果已经有对象，就覆盖一下属性
      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);
        }
        // 如果 Configuration 不存在，但是配置了 configLocation 属性，
        // 就根据mybatis-config.xml的文件路径，构建一个xmlConfigBuilder对象。
      } else if (this.configLocation != null) {
        
        xmlConfigBuilder = new XMLConfigBuilder(this.configLocation.getInputStream(), null, this.configurationProperties);
        targetConfiguration = xmlConfigBuilder.getConfiguration();
        // 否则，Configuration 对象不存在，configLocation 路径也没有，
        // 只能使用默认属性去构建去给configurationProperties赋值。
      } else {
        
        LOGGER.debug(() -> "Property 'configuration' or 'configLocation' not specified,using default MyBatis Configuration");
        targetConfiguration = new Configuration();
        Optional.ofNullable(this.configurationProperties).ifPresent(targetConfiguration::setVariables);
      }
      
      // 基于当前factory 对象里面已有的属性，对targetConfiguration对象里面属性的赋值。
      Optional.ofNullable(this.objectFactory).ifPresent(targetConfiguration::setObjectFactory);
      Optional.ofNullable(this.objectWrapperFactory).
                     ifPresent(targetConfiguration::setObjectWrapperFactory);
      Optional.ofNullable(this.vfs).ifPresent(targetConfiguration::setVfsImpl);
    
      if (hasLength(this.typeAliasesPackage)) {
        
        String[] typeAliasPackageArray = tokenizeToStringArray(this.typeAliasesPackage,
            ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
        Stream.of(typeAliasPackageArray).forEach(packageToScan -> {
        
          targetConfiguration.getTypeAliasRegistry().registerAliases(packageToScan,
              typeAliasesSuperType == null ? Object.class : typeAliasesSuperType);
          LOGGER.debug(() -> "Scanned package: '" + packageToScan + "' for aliases");
        });
      }
    
      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)) {
        
        String[] typeHandlersPackageArray = tokenizeToStringArray(this.typeHandlersPackage,
            ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
        Stream.of(typeHandlersPackageArray).forEach(packageToScan -> {
        
          targetConfiguration.getTypeHandlerRegistry().register(packageToScan);
          LOGGER.debug(() -> "Scanned package: '" + packageToScan + "' for type handlers");
        });
      }
    
      if (!isEmpty(this.typeHandlers)) {
        
        Stream.of(this.typeHandlers).forEach(typeHandler -> {
        
          targetConfiguration.getTypeHandlerRegistry().register(typeHandler);
          LOGGER.debug(() -> "Registered type handler: '" + typeHandler + "'");
        });
      }
    
      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);
      // 如果xmlConfigBuilder 不为空，也就是上面的第二种情况，
      if (xmlConfigBuilder != null) {
        
        try {
        
          // 调用了xmlConfigBuilder.parse()去解析配置文件，最终会返回解析好的Configuration对象
          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();
        }
      }
    
      // 如果没有明确指定事务工厂 ，默认使用pringManagedTransactionFactory。
      // 它创建的 SpringManagedTransaction 也有getConnection()和close()方法
      // <property name="transactionFactory" value="" />
      targetConfiguration.setEnvironment(new Environment(this.environment,
          this.transactionFactory == null ? new SpringManagedTransactionFactory() : this.transactionFactory,this.dataSource));
    
      if (!isEmpty(this.mapperLocations)) {
        
        for (Resource mapperLocation : this.mapperLocations) {
        
          if (mapperLocation == null) {
        
            continue;
          }
    
          try {
        
            XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(mapperLocation.getInputStream(),
             targetConfiguration, mapperLocation.toString(), targetConfiguration.getSqlFragments());
            // 调用xmlMapperBuilder.parse()，
            // 它的作用是把接口和对应的MapperProxyFactory 注册到MapperRegistry 中。
            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 or no matching resources found");
      }
    
      // 最后调用 sqlSessionFactoryBuilder.build() 返回一个 DefaultSqlSessionFactory。
      return this.sqlSessionFactoryBuilder.build(targetConfiguration);
    }

可以看到最终返回一个 SqlSessionFactory 的默认实现 DefaultSqlSessionFactory。

> 最后再梳理一下 IOC 容器 getBean() 获取 SqlSessionFactory 的调用链路：  
> getBean() --> SqlSessionFactoryBean\#getObject() --> afterPropertiesSet() --> buildSqlSessionFactory() ==> DefaultSqlSessionFactory

[Link 1]: https://blog.csdn.net/weixin_43935927/article/details/111399479
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[Link 2]: https://blog.csdn.net/maclaren001/article/details/37039749
[Link 3]: https://blog.csdn.net/weixin_43935927/article/details/110508417