Mybatis源码解析之配置解析

[上一篇]：Mybatis源码解析之Spring获取Mapper过程

菜菜的上一篇《Mybatis源码解析之Spring获取Mapper过程》主要介绍的是MapperScan,并从中知道了Spring与MyBatis如何连接起来的，这篇菜菜继续看配置文件中配置的SqlSessionFactoryBean,并介绍解析MaBatis中配置的xml信息。

问题

MyBatis中的配置文件是在哪步进行解析的？

揭秘答案-源码

这里再次贴出上篇中配置文件中部分代码

@Bean
  public SqlSessionFactoryBean sqlSessionFactoryBean(DataSource dataSource, ApplicationContext applicationContext) throws Exception {
    SqlSessionFactoryBean sessionFactory = new SqlSessionFactoryBean();
    sessionFactory.setDataSource(dataSource);
    sessionFactory.setConfigLocation(applicationContext.getResource("classpath:mybatis-config.xml"));
    sessionFactory.afterPropertiesSet();
    sessionFactory.setPlugins(new Interceptor[] { new PagerInterceptor()});
    return sessionFactory;
  }

配置文件中配置了SqlSessionFactoryBean的bean,Spring在启动的时候就会执行sqlSessionFactoryBean(DataSource dataSource, ApplicationContext applicationContext)来创建Bean的实例，该方法中前面都是对属性进行设置，主要看sessionFactory.afterPropertiesSet();
afterPropertiesSet()是Spring中InitializingBean中的方法,Spring会在初始化Bean时所有的属性被初始化后调用该方法。SqlSessionFactoryBean中afterPropertiesSet()方法中最重要的是调用buildSqlSessionFactory()方法，下面具体看下buildSqlSessionFactory方法

@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();
  }

/**
   * Build a {@code SqlSessionFactory} instance.
   *
   * The default implementation uses the standard MyBatis {@code XMLConfigBuilder} API to build a
   * {@code SqlSessionFactory} instance based on an Reader.
   * Since 1.3.0, it can be specified a {@link Configuration} instance directly(without config file).
   *
   * @return SqlSessionFactory
   * @throws IOException if loading the config file failed
   */
 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 + "'");
        }
      }
    }
//如果添加了plugins，最终会将plugins加入interceptorChain
    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);
    }
//如果配置了config文件的位置就会去解析改文件一般是mybatis-config.xml文件
    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));
//如果配置了Mapper文件路径就会去解析Mapper
    if (!isEmpty(this.mapperLocations)) {
      for (Resource mapperLocation : this.mapperLocations) {
        if (mapperLocation == null) {
          continue;
        }

        try {
          XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(mapperLocation.getInputStream(),
              configuration, mapperLocation.toString(), configuration.getSqlFragments());
          xmlMapperBuilder.parse();
        } catch (Exception e) {
          throw new NestedIOException("Failed to parse mapping resource: '" + mapperLocation + "'", e);
        } finally {
          ErrorContext.instance().reset();
        }

        if (LOGGER.isDebugEnabled()) {
          LOGGER.debug("Parsed mapper file: '" + mapperLocation + "'");
        }
      }
    } else {
      if (LOGGER.isDebugEnabled()) {
        LOGGER.debug("Property 'mapperLocations' was not specified or no matching resources found");
      }
    }

    return this.sqlSessionFactoryBuilder.build(configuration);
  }


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

在buildSqlSessionFactory中有两个解析xml文件的地方一个是xmlConfigBuilder解析config文件，另外一个是xmlMapperBuilder用来解析mapper文件。

Spring与MyBatis整合后在上一篇中没有设置mapperLocation，所以真正解析Mapper文件的地方并不在这，而是在MapperFactoryBean的checkDaoConfig()里（后面会详细说明）

buildSqlSessionFactory最后一步是返回SqlSessionFactory，我们看到返回的是DefaultSqlSessionFactory，Mybatis源码解析之SqlSession来自何方中知道SqlSessionFactoryBean是个factoryBean，在Spring实例化bean时会调用getObject()方法，而它的getObject()返回的就是buildSqlSessionFactory创建的DefaultSqlSessionFactory，这样在Spring中就有了拥有了SqlSessionFactory。

那么，Mapper文件的解析为什么会是在MapperFactoryBean的checkDaoConfig()里呢

我们首先看下MapperFactoryBean的继承层次关系

image.png

再来看下DaoSupport这个类

public abstract class DaoSupport implements InitializingBean {
    protected final Log logger = LogFactory.getLog(this.getClass());

    public DaoSupport() {
    }

    public final void afterPropertiesSet() throws IllegalArgumentException, BeanInitializationException {
        this.checkDaoConfig();

        try {
            this.initDao();
        } catch (Exception var2) {
            throw new BeanInitializationException("Initialization of DAO failed", var2);
        }
    }

    protected abstract void checkDaoConfig() throws IllegalArgumentException;

    protected void initDao() throws Exception {
    }
}

DaoSupport实现了InitializingBean，并使用模板方法设计模式定义了两个模板方法checkDaoConfig()与initDao()

由于DaoSupport实现了InitializingBean所以MapperFactoryBean初始化(为什么进行会创建这个bean在下一篇中有讲到)属性完成后就会调用DaoSupport里的afterPropertiesSet()方法afterPropertiesSet方法首先调用了this.checkDaoConfig();而MapperFactoryBean实现了该方法,如下：

/**
   * {@inheritDoc}
   */
  @Override
  protected void checkDaoConfig() {
    super.checkDaoConfig();

    notNull(this.mapperInterface, "Property 'mapperInterface' is required");

    Configuration configuration = getSqlSession().getConfiguration();
    if (this.addToConfig && !configuration.hasMapper(this.mapperInterface)) {
      try {
        configuration.addMapper(this.mapperInterface);
      } catch (Exception e) {
        logger.error("Error while adding the mapper '" + this.mapperInterface + "' to configuration.", e);
        throw new IllegalArgumentException(e);
      } finally {
        ErrorContext.instance().reset();
      }
    }
  }

checkDaoConfig()中最重要的方法是configuration.addMapper(this.mapperInterface);为了减少篇幅下面一次性将所有调用到的源码知道解析mapper贴出

//Configuration
public <T> void addMapper(Class<T> type) {
    mapperRegistry.addMapper(type);
  }

//MapperRegistry
public <T> void addMapper(Class<T> type) {
    if (type.isInterface()) {
      if (hasMapper(type)) {
        throw new BindingException("Type " + type + " is already known to the MapperRegistry.");
      }
      boolean loadCompleted = false;
      try {
        knownMappers.put(type, new MapperProxyFactory<T>(type));
        // It's important that the type is added before the parser is run
        // otherwise the binding may automatically be attempted by the
        // mapper parser. If the type is already known, it won't try.
        MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type);
//这里进行解析
        parser.parse();
        loadCompleted = true;
      } finally {
        if (!loadCompleted) {
          knownMappers.remove(type);
        }
      }
    }
  }

//MapperAnnotationBuilder
 public void parse() {
    String resource = type.toString();
    if (!configuration.isResourceLoaded(resource)) {
//先解析xml中的sql
      loadXmlResource();
      configuration.addLoadedResource(resource);
      assistant.setCurrentNamespace(type.getName());
      parseCache();
      parseCacheRef();
      Method[] methods = type.getMethods();
      for (Method method : methods) {
        try {
          // issue #237
          if (!method.isBridge()) {
         //解析注解中的sql
            parseStatement(method);
          }
        } catch (IncompleteElementException e) {
          configuration.addIncompleteMethod(new MethodResolver(this, method));
        }
      }
    }
    parsePendingMethods();
  }
private void loadXmlResource() {
    // Spring may not know the real resource name so we check a flag
    // to prevent loading again a resource twice
    // this flag is set at XMLMapperBuilder#bindMapperForNamespace
    if (!configuration.isResourceLoaded("namespace:" + type.getName())) {
      String xmlResource = type.getName().replace('.', '/') + ".xml";
      InputStream inputStream = null;
      try {
        inputStream = Resources.getResourceAsStream(type.getClassLoader(), xmlResource);
      } catch (IOException e) {
        // ignore, resource is not required
      }
      if (inputStream != null) {
        XMLMapperBuilder xmlParser = new XMLMapperBuilder(inputStream, assistant.getConfiguration(), xmlResource, configuration.getSqlFragments(), type.getName());
        xmlParser.parse();
      }
    }
  }

//XMLMapperBuilder
public void parse() {
    //这里就是具体解析element了有兴趣自己可以看下
    if (!configuration.isResourceLoaded(resource)) {
      configurationElement(parser.evalNode("/mapper"));
      configuration.addLoadedResource(resource);
      bindMapperForNamespace();
    }

    parsePendingResultMaps();
    parsePendingChacheRefs();
    parsePendingStatements();
  }

菜菜相信只要找到了是在configuration.addMapper(this.mapperInterface)里去解析Mapper文件以及Spring怎么进入configuration.addMapper(this.mapperInterface)的，后面的具体怎么解析相信大家都能看的明白，只需要记住一点，Mybatis的所有配置信息都存放在Configuration里。

如有错误，欢迎各位大佬斧正！
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