mybatis-spring-boot-starter源码学习--初始化mybatis

一、springboot starter常规操作,项目在启动的时候会扫描 jar 包 META-INF 文件夹下的 spring.factories 文件,然后去加载对应的配置文件中的类进行初始化各项需要的变量。

mybatis-spring-boot-starter 包中查找对应的spring.factories 文件内容如下:

# Auto Configure
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.mybatis.spring.boot.autoconfigure.MybatisAutoConfiguration

二、MybatisAutoConfiguration 为加载mybatis核心的入口。

   (1)首先看一下该类中的注解

//等价于XML中配置beans
@Configuration
//当给定的类名在类路径上存在,则实例化当前Bean
@ConditionalOnClass({ SqlSessionFactory.class, SqlSessionFactoryBean.class })
//当给定的在bean存在时,则实例化当前Bean
@ConditionalOnBean(DataSource.class)
//使使用 @ConfigurationProperties 注解的类生效。
@EnableConfigurationProperties(MybatisProperties.class)
//在DataSourceAutoConfiguration类加载之后自动注入
@AutoConfigureAfter(DataSourceAutoConfiguration.class)
public class MybatisAutoConfiguration {
       ...........
}

 (2)加载SqlSessionFactory

  @Bean //等价于xml中的bean标签
  @ConditionalOnMissingBean// 在BeanFactory中不存在SqlSessionFactory 就执行下面的创建逻辑
  public SqlSessionFactory sqlSessionFactory(DataSource dataSource) throws Exception {
    SqlSessionFactoryBean factory = new SqlSessionFactoryBean();
    factory.setDataSource(dataSource);
    factory.setVfs(SpringBootVFS.class);
    if (StringUtils.hasText(this.properties.getConfigLocation())) {
      factory.setConfigLocation(this.resourceLoader.getResource(this.properties.getConfigLocation()));
    }
    factory.setConfiguration(properties.getConfiguration());
    if (!ObjectUtils.isEmpty(this.interceptors)) {
      factory.setPlugins(this.interceptors);
    }
    if (this.databaseIdProvider != null) {
      factory.setDatabaseIdProvider(this.databaseIdProvider);
    }
    if (StringUtils.hasLength(this.properties.getTypeAliasesPackage())) {
      factory.setTypeAliasesPackage(this.properties.getTypeAliasesPackage());
    }
    if (StringUtils.hasLength(this.properties.getTypeHandlersPackage())) {
      factory.setTypeHandlersPackage(this.properties.getTypeHandlersPackage());
    }
    if (!ObjectUtils.isEmpty(this.properties.resolveMapperLocations())) {
      factory.setMapperLocations(this.properties.resolveMapperLocations());
    }
       //用于创建sqlSessionFactory
    return factory.getObject();
  }
  // factory.getObject(); 方法,主要是用于创建sqlSessionFactory
  @Override
  public SqlSessionFactory getObject() throws Exception {
    //判断sqlSessionFactory是否存在
    if (this.sqlSessionFactory == null) {
      afterPropertiesSet();
    }

    return this.sqlSessionFactory;
  }

//sqlSessionFactory 为空执行创建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();
  }
//创建sqlSessionFactory的过程
 protected SqlSessionFactory buildSqlSessionFactory() throws IOException {

    Configuration configuration;

    XMLConfigBuilder xmlConfigBuilder = null;
    if (this.configuration != null) {
      configuration = this.configuration;
      if (configuration.getVariables() == null) {
        configuration.setVariables(this.configurationProperties);
      } else if (this.configurationProperties != null) {
        configuration.getVariables().putAll(this.configurationProperties);
      }
    } else if (this.configLocation != null) {
      xmlConfigBuilder = new XMLConfigBuilder(this.configLocation.getInputStream(), null, this.configurationProperties);
      configuration = xmlConfigBuilder.getConfiguration();
    } else {
      if (LOGGER.isDebugEnabled()) {
        LOGGER.debug("Property `configuration` or '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 (this.vfs != null) {
      configuration.setVfsImpl(this.vfs);
    }

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

    if (this.cache != null) {
      configuration.addCache(this.cache);
    }

    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 (!isEmpty(this.mapperLocations)) {
      for (Resource mapperLocation : this.mapperLocations) {
        if (mapperLocation == null) {
          continue;
        }

        try {
        //解析*mapper.xml文件中的标签,并将