Mybatis启动流程

Mybatis启动流程 ----- (SpringBoot)

初次查看源码，不足处请指教。

在mybatis-spring-boot-autoconfigure包META-INF目录下，spring.factories文件中配置这样一段配置：

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

SpringBoot项目在启动的时候，会自动加载这个文件中配置的MybatisAutoConfiguration类：

@org.springframework.context.annotation.Configuration
@ConditionalOnClass({ SqlSessionFactory.class, SqlSessionFactoryBean.class })
@ConditionalOnSingleCandidate(DataSource.class)
@EnableConfigurationProperties(MybatisProperties.class)
@AutoConfigureAfter(DataSourceAutoConfiguration.class)
public class MybatisAutoConfiguration implements InitializingBean {

  @Bean
  @ConditionalOnMissingBean
  public SqlSessionFactory sqlSessionFactory(DataSource dataSource) throws Exception {
    SqlSessionFactoryBean factory = new SqlSessionFactoryBean();
    ......
    // 向SqlSessionFactoryBean设置实体类的别名信息
    if (StringUtils.hasLength(this.properties.getTypeAliasesPackage())) {
      factory.setTypeAliasesPackage(this.properties.getTypeAliasesPackage());
    }
    ......
    // 向SqlSessionFactoryBean设置xml映射文件信息
    if (!ObjectUtils.isEmpty(this.properties.resolveMapperLocations())) {
      factory.setMapperLocations(this.properties.resolveMapperLocations());
    }
    return factory.getObject();
  }
}

刚接触Mybatis时就学习SqlSessionFactory是核心，在配置类中，是通过SqlSessionFactoryBean的getObject()创建创建SqlSessionFactory的，方法上使用@ConditionalOnMissingBean注解，表示容器中不存在SqlSessionFactory时才会执行此方法，保证SqlSessionFactory是单例。

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

    return this.sqlSessionFactory;
  }

SqlSessionFactoryBean的getObject()是通过afterPropertiesSet()方法创建sqlSessionFactory的，继续往下看：

  public void afterPropertiesSet() throws Exception {
    ......
    this.sqlSessionFactory = buildSqlSessionFactory();
  }

在afterPropertiesSet()方法中，通过buildSqlSessionFactory()方法创建sqlSessionFactory；

  protected SqlSessionFactory buildSqlSessionFactory() throws IOException {

    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);

    // 前面在MybatisAutoConfiguration设置的实体类别名在这里开始初始化
    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 + "'");
      });
    }

    // 前面在MybatisAutoConfiguration也有设置Mybatis的插件，这里初始化
    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);

    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));
	
    // 前面在MybatisAutoConfiguration中设置的xml映射文件信息在这里开始加载、解析，将mapper接口和xml映射文件中的方法、sql、缓存等信息绑定到一起
    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());
          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");
    }

    return this.sqlSessionFactoryBuilder.build(targetConfiguration);
  }

在构建sqlSessionFactory之前，先将别名配置、插件、xml、接口等解析完成存储在MappedStatement中，后续使用到sqlSessionFactory直接获取即可。

public SqlSessionFactory build(Configuration config) {
  return new DefaultSqlSessionFactory(config);
}