Spring整合mybatis源码剖析

整合原理图：

@MapperScan底层原理剖析

主要作用：会将MapperScannerConfigurer注册到spring容器中。

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
@Import(MapperScannerRegistrar.class) // 点进去
@Repeatable(MapperScans.class)
public @interface MapperScan {
    // 代码省略
}

public class MapperScannerRegistrar implements ImportBeanDefinitionRegistrar, ResourceLoaderAware {

  /**
   * {@inheritDoc}
   */
  @Override
  public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
    AnnotationAttributes mapperScanAttrs = AnnotationAttributes
        .fromMap(importingClassMetadata.getAnnotationAttributes(MapperScan.class.getName()));
    if (mapperScanAttrs != null) {
       // 注册bean的定义，也就是向spring容器中注册bean
      registerBeanDefinitions(importingClassMetadata, mapperScanAttrs, registry,
          generateBaseBeanName(importingClassMetadata, 0));
    }
  }

  void registerBeanDefinitions(AnnotationMetadata annoMeta, AnnotationAttributes annoAttrs,
      BeanDefinitionRegistry registry, String beanName) {

      // 会加载MapperScannerConfigurer
    BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition(MapperScannerConfigurer.class);
    builder.addPropertyValue("processPropertyPlaceHolders", true);

      // 下面是一些属性赋值
    Class<? extends Annotation> annotationClass = annoAttrs.getClass("annotationClass");
    if (!Annotation.class.equals(annotationClass)) {
      builder.addPropertyValue("annotationClass", annotationClass);
    }

    Class<?> markerInterface = annoAttrs.getClass("markerInterface");
    if (!Class.class.equals(markerInterface)) {
      builder.addPropertyValue("markerInterface", markerInterface);
    }

    Class<? extends BeanNameGenerator> generatorClass = annoAttrs.getClass("nameGenerator");
    if (!BeanNameGenerator.class.equals(generatorClass)) {
      builder.addPropertyValue("nameGenerator", BeanUtils.instantiateClass(generatorClass));
    }

    Class<? extends MapperFactoryBean> mapperFactoryBeanClass = annoAttrs.getClass("factoryBean");
    if (!MapperFactoryBean.class.equals(mapperFactoryBeanClass)) {
      builder.addPropertyValue("mapperFactoryBeanClass", mapperFactoryBeanClass);
    }

    String sqlSessionTemplateRef = annoAttrs.getString("sqlSessionTemplateRef");
    if (StringUtils.hasText(sqlSessionTemplateRef)) {
      builder.addPropertyValue("sqlSessionTemplateBeanName", annoAttrs.getString("sqlSessionTemplateRef"));
    }

    String sqlSessionFactoryRef = annoAttrs.getString("sqlSessionFactoryRef");
    if (StringUtils.hasText(sqlSessionFactoryRef)) {
      builder.addPropertyValue("sqlSessionFactoryBeanName", annoAttrs.getString("sqlSessionFactoryRef"));
    }

    List<String> basePackages = new ArrayList<>();
    basePackages.addAll(
        Arrays.stream(annoAttrs.getStringArray("value")).filter(StringUtils::hasText).collect(Collectors.toList()));

    basePackages.addAll(Arrays.stream(annoAttrs.getStringArray("basePackages")).filter(StringUtils::hasText)
        .collect(Collectors.toList()));

    basePackages.addAll(Arrays.stream(annoAttrs.getClassArray("basePackageClasses")).map(ClassUtils::getPackageName)
        .collect(Collectors.toList()));

    if (basePackages.isEmpty()) {
      basePackages.add(getDefaultBasePackage(annoMeta));
    }

    String lazyInitialization = annoAttrs.getString("lazyInitialization");
    if (StringUtils.hasText(lazyInitialization)) {
      builder.addPropertyValue("lazyInitialization", lazyInitialization);
    }

    String defaultScope = annoAttrs.getString("defaultScope");
    if (!AbstractBeanDefinition.SCOPE_DEFAULT.equals(defaultScope)) {
      builder.addPropertyValue("defaultScope", defaultScope);
    }

    builder.addPropertyValue("basePackage", StringUtils.collectionToCommaDelimitedString(basePackages));

    // for spring-native
    builder.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
      
      // 会将MapperScannerConfigurer注册到spring容器中，重点
    registry.registerBeanDefinition(beanName, builder.getBeanDefinition());

  }

  // ...代码省略

}

MapperScannerConfigurer底层原理剖析

org.springframework.beans.factory.support.BeanDefinitionRegistryPostProcessor#postProcessBeanDefinitionRegistry

org.mybatis.spring.mapper.MapperScannerConfigurer#postProcessBeanDefinitionRegistry实现的是上面接口的方法

@Override
  public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {
    if (this.processPropertyPlaceHolders) {
      processPropertyPlaceHolders();
    }

     // 一层一层点进去，会看到使用的是spring的ClassPathBeanDefinitionScanner扫描器
    ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry);
    scanner.setAddToConfig(this.addToConfig);
    scanner.setAnnotationClass(this.annotationClass);
    scanner.setMarkerInterface(this.markerInterface);
    scanner.setSqlSessionFactory(this.sqlSessionFactory);
    scanner.setSqlSessionTemplate(this.sqlSessionTemplate);
    scanner.setSqlSessionFactoryBeanName(this.sqlSessionFactoryBeanName);
    scanner.setSqlSessionTemplateBeanName(this.sqlSessionTemplateBeanName);
    scanner.setResourceLoader(this.applicationContext);
    scanner.setBeanNameGenerator(this.nameGenerator);
    scanner.setMapperFactoryBeanClass(this.mapperFactoryBeanClass);
    if (StringUtils.hasText(lazyInitialization)) {
      scanner.setLazyInitialization(Boolean.valueOf(lazyInitialization));
    }
    if (StringUtils.hasText(defaultScope)) {
      scanner.setDefaultScope(defaultScope);
    }
    scanner.registerFilters();
    // 扫描@MapperScan("com.coding.spring.mybatis")包下的类，并转换成bean的定义
      // 点进去
    scanner.scan(
        StringUtils.tokenizeToStringArray(this.basePackage, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS));
  }

org.springframework.beans.factory.InitializingBean#afterPropertiesSet

org.mybatis.spring.mapper.MapperScannerConfigurer#afterPropertiesSet实现的是上面接口的方法

// 验证basePackage不能为空
@Override
public void afterPropertiesSet() throws Exception {
  notNull(this.basePackage, "Property 'basePackage' is required");
}

org.springframework.beans.factory.config.BeanFactoryPostProcessor#postProcessBeanFactory

org.mybatis.spring.mapper.MapperScannerConfigurer#postProcessBeanFactory实现的是上面接口的方法

@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
  // left intentionally blank
  // 故意留白，什么也没有干
}

org.springframework.context.annotation.ClassPathBeanDefinitionScanner#scan

public int scan(String... basePackages) {
    int beanCountAtScanStart = this.registry.getBeanDefinitionCount();

    doScan(basePackages); // 注意这里相当于是一个模版方法，ClassPathMapperScanner类有重写

    // Register annotation config processors, if necessary.
    if (this.includeAnnotationConfig) {
       AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);
    }

    return (this.registry.getBeanDefinitionCount() - beanCountAtScanStart);
}

org.mybatis.spring.mapper.ClassPathMapperScanner#doScan

@Override
  public Set<BeanDefinitionHolder> doScan(String... basePackages) {
      // 通过扫描，获取到bean的定义
    Set<BeanDefinitionHolder> beanDefinitions = super.doScan(basePackages);

    if (beanDefinitions.isEmpty()) {
      LOGGER.warn(() -> "No MyBatis mapper was found in '" + Arrays.toString(basePackages)
          + "' package. Please check your configuration.");
    } else {
        // 处理bean的定义
      processBeanDefinitions(beanDefinitions);
    }

    return beanDefinitions;
  }

private void processBeanDefinitions(Set<BeanDefinitionHolder> beanDefinitions) {
  AbstractBeanDefinition definition;
  BeanDefinitionRegistry registry = getRegistry();
    // 遍历beanDefinition
  for (BeanDefinitionHolder holder : beanDefinitions) {
    definition = (AbstractBeanDefinition) holder.getBeanDefinition();
      // 下面的主要逻辑就是给beanDefinition设置一些属性
    boolean scopedProxy = false;
    if (ScopedProxyFactoryBean.class.getName().equals(definition.getBeanClassName())) {
      definition = (AbstractBeanDefinition) Optional
          .ofNullable(((RootBeanDefinition) definition).getDecoratedDefinition())
          .map(BeanDefinitionHolder::getBeanDefinition).orElseThrow(() -> new IllegalStateException(
              "The target bean definition of scoped proxy bean not found. Root bean definition[" + holder + "]"));
      scopedProxy = true;
    }
    String beanClassName = definition.getBeanClassName();
    LOGGER.debug(() -> "Creating MapperFactoryBean with name '" + holder.getBeanName() + "' and '" + beanClassName
        + "' mapperInterface");

    // the mapper interface is the original class of the bean
    // but, the actual class of the bean is MapperFactoryBean
    definition.getConstructorArgumentValues().addGenericArgumentValue(beanClassName); // issue #59
    try {
      // for spring-native
      definition.getPropertyValues().add("mapperInterface", Resources.classForName(beanClassName));
    } catch (ClassNotFoundException ignore) {
      // ignore
    }

      // 将mapperFactoryBean类型赋值给beanDefinition
      // MapperFactoryBean实现了FactoryBean接口，最后使用getObject方法通过jdk动态代理的方式创建mapper对象
    definition.setBeanClass(this.mapperFactoryBeanClass);

    definition.getPropertyValues().add("addToConfig", this.addToConfig);

    // Attribute for MockitoPostProcessor
    // https://github.com/mybatis/spring-boot-starter/issues/475
    definition.setAttribute(FACTORY_BEAN_OBJECT_TYPE, beanClassName);

    boolean explicitFactoryUsed = false;
    if (StringUtils.hasText(this.sqlSessionFactoryBeanName)) {
      definition.getPropertyValues().add("sqlSessionFactory",
          new RuntimeBeanReference(this.sqlSessionFactoryBeanName));
      explicitFactoryUsed = true;
    } else if (this.sqlSessionFactory != null) {
      definition.getPropertyValues().add("sqlSessionFactory", this.sqlSessionFactory);
      explicitFactoryUsed = true;
    }

    if (StringUtils.hasText(this.sqlSessionTemplateBeanName)) {
      if (explicitFactoryUsed) {
        LOGGER.warn(
            () -> "Cannot use both: sqlSessionTemplate and sqlSessionFactory together. sqlSessionFactory is ignored.");
      }
      definition.getPropertyValues().add("sqlSessionTemplate",
          new RuntimeBeanReference(this.sqlSessionTemplateBeanName));
      explicitFactoryUsed = true;
    } else if (this.sqlSessionTemplate != null) {
      if (explicitFactoryUsed) {
        LOGGER.warn(
            () -> "Cannot use both: sqlSessionTemplate and sqlSessionFactory together. sqlSessionFactory is ignored.");
      }
      definition.getPropertyValues().add("sqlSessionTemplate", this.sqlSessionTemplate);
      explicitFactoryUsed = true;
    }

    if (!explicitFactoryUsed) {
      LOGGER.debug(() -> "Enabling autowire by type for MapperFactoryBean with name '" + holder.getBeanName() + "'.");
      definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE);
    }

    definition.setLazyInit(lazyInitialization);

    if (scopedProxy) {
      continue;
    }

    if (ConfigurableBeanFactory.SCOPE_SINGLETON.equals(definition.getScope()) && defaultScope != null) {
      definition.setScope(defaultScope);
    }

    if (!definition.isSingleton()) {
      BeanDefinitionHolder proxyHolder = ScopedProxyUtils.createScopedProxy(holder, registry, true);
      if (registry.containsBeanDefinition(proxyHolder.getBeanName())) {
        registry.removeBeanDefinition(proxyHolder.getBeanName());
      }
      registry.registerBeanDefinition(proxyHolder.getBeanName(), proxyHolder.getBeanDefinition());
    }

  }
}

SqlSessionFactoryBean 底层原理剖析

@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");

   // 由此可见，重点关注buildSqlSessionFactory()方法
  this.sqlSessionFactory = buildSqlSessionFactory();
}

// 由此可见，重点关注buildSqlSessionFactory()方法

// 该方法的目的是为了创建SqlSessionFactory
protected SqlSessionFactory buildSqlSessionFactory() throws Exception {

  final Configuration targetConfiguration;

   // 下面主要是给targetConfiguration设置属性信息
  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);

  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));

  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());
          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.");
  }

    // 使用建造者模式创建SqlSessionFactory，点进去
  return this.sqlSessionFactoryBuilder.build(targetConfiguration);
}

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

创建出来SqlSessionFactory之后，将器纳入到spring容器中进行管理。紧接着我们可以通过SqlSessionFactory拿到SqlSession对象进而操作数据库了。