myBatis源码之XMLConfigBuilder

XMLConfigBuilder是对mybatis的配置文件进行解析的类，会对myabtis解析后的信息存放在Configuration对象中，Configuration对象会贯穿整个mybatis的执行流程，为mybatis的执行过程提供各种需要的配置信息。

/**
 * @author Clinton Begin
 */
public class XMLConfigBuilder extends BaseBuilder {

  private boolean parsed;
  private XPathParser parser;
  private String environment;

  public XMLConfigBuilder(Reader reader) {
    this(reader, null, null);
  }

  public XMLConfigBuilder(Reader reader, String environment) {
    this(reader, environment, null);
  }

  public XMLConfigBuilder(Reader reader, String environment, Properties props) {
    this(new XPathParser(reader, true, props, new XMLMapperEntityResolver()), environment, props);
  }

  public XMLConfigBuilder(InputStream inputStream) {
    this(inputStream, null, null);
  }

  public XMLConfigBuilder(InputStream inputStream, String environment) {
    this(inputStream, environment, null);
  }

  public XMLConfigBuilder(InputStream inputStream, String environment, Properties props) {
    this(new XPathParser(inputStream, true, props, new XMLMapperEntityResolver()), environment, props);
  }

  private XMLConfigBuilder(XPathParser parser, String environment, Properties props) {
    super(new Configuration());
    ErrorContext.instance().resource("SQL Mapper Configuration");
    this.configuration.setVariables(props);
    this.parsed = false;
    this.environment = environment;
    this.parser = parser;
  }

  public Configuration parse() {
    if (parsed) {
      throw new BuilderException("Each XMLConfigBuilder can only be used once.");
    }
    parsed = true;
	//mybatis的配置文件的根节点是configuration，从根节点开始解析配置文件
    parseConfiguration(parser.evalNode("/configuration"));
    return configuration;
  }

  private void parseConfiguration(XNode root) {
    try {
	  //解析子节点properties
      propertiesElement(root.evalNode("properties")); //issue #117 read properties first
	  //解析子节点typeAliases 别名
      typeAliasesElement(root.evalNode("typeAliases"));
	  //解析子节点plugins 插件
      pluginElement(root.evalNode("plugins"));
	  //解析子节点objectFactory mybatis为结果创建对象时都会用到objectFactory
      objectFactoryElement(root.evalNode("objectFactory"));
	  //解析子节点objectWrapperFactory
      objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
	  //解析settings定义一些全局性的配置
      settingsElement(root.evalNode("settings"));
	  //解析environments 可以配置多个运行环境，但是每个SqlSessionFactory 实例只能选择一个运行环境
      environmentsElement(root.evalNode("environments")); // read it after objectFactory and objectWrapperFactory issue #631
	  //解析databaseIdProvider MyBatis能够执行不同的语句取决于你提供的数据库供应商。许多数据库供应商的支持是基于databaseId映射
      databaseIdProviderElement(root.evalNode("databaseIdProvider"));
	  //解析typeHandlers 当MyBatis设置参数到PreparedStatement 或者从ResultSet 结果集中取得值时，就会使用TypeHandler  来处理数据库类型与java 类型之间转换
      typeHandlerElement(root.evalNode("typeHandlers"));
	  //解析mappers 主要的crud操作都是在mappers中定义的
      mapperElement(root.evalNode("mappers"));
    } catch (Exception e) {
      throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
    }
  }
  //类别名解析
  private void typeAliasesElement(XNode parent) {
    if (parent != null) {
      for (XNode child : parent.getChildren()) {
		//如果子节点是package,那么就获取package节点的name属性
        if ("package".equals(child.getName())) {
          String typeAliasPackage = child.getStringAttribute("name");
          configuration.getTypeAliasRegistry().registerAliases(typeAliasPackage);
        } else {
		//如果子节点是typeAlias节点，那么就获取alias属性和type的属性
          String alias = child.getStringAttribute("alias");
          String type = child.getStringAttribute("type");
          try {
			//通过type的值来加载获得类
            Class<?> clazz = Resources.classForName(type);
            if (alias == null) {
			//typeAliasRegistry会进行别名注册
              typeAliasRegistry.registerAlias(clazz);
            } else {
              typeAliasRegistry.registerAlias(alias, clazz);
            }
          } catch (ClassNotFoundException e) {
            throw new BuilderException("Error registering typeAlias for '" + alias + "'. Cause: " + e, e);
          }
        }
      }
    }
  }
  //插件元素解析
  private void pluginElement(XNode parent) throws Exception {
    if (parent != null) {
      for (XNode child : parent.getChildren()) {
        String interceptor = child.getStringAttribute("interceptor");
        Properties properties = child.getChildrenAsProperties();
        Interceptor interceptorInstance = (Interceptor) resolveClass(interceptor).newInstance();
        interceptorInstance.setProperties(properties);
        configuration.addInterceptor(interceptorInstance);
      }
    }
  }
  //对象工厂元素解析
  private void objectFactoryElement(XNode context) throws Exception {
    if (context != null) {
      String type = context.getStringAttribute("type");
      Properties properties = context.getChildrenAsProperties();
      ObjectFactory factory = (ObjectFactory) resolveClass(type).newInstance();
      factory.setProperties(properties);
      configuration.setObjectFactory(factory);
    }
  }
  //对象打包工厂元素解析
  private void objectWrapperFactoryElement(XNode context) throws Exception {
    if (context != null) {
      String type = context.getStringAttribute("type");
      ObjectWrapperFactory factory = (ObjectWrapperFactory) resolveClass(type).newInstance();
      configuration.setObjectWrapperFactory(factory);
    }
  }
  //
  private void propertiesElement(XNode context) throws Exception {
    if (context != null) {
      Properties defaults = context.getChildrenAsProperties();
      String resource = context.getStringAttribute("resource");
      String url = context.getStringAttribute("url");
      if (resource != null && url != null) {
        throw new BuilderException("The properties element cannot specify both a URL and a resource based property file reference.  Please specify one or the other.");
      }
      if (resource != null) {
        defaults.putAll(Resources.getResourceAsProperties(resource));
      } else if (url != null) {
        defaults.putAll(Resources.getUrlAsProperties(url));
      }
      Properties vars = configuration.getVariables();
      if (vars != null) {
        defaults.putAll(vars);
      }
      parser.setVariables(defaults);
      configuration.setVariables(defaults);
    }
  }
  //配置元素解析
  private void settingsElement(XNode context) throws Exception {
    if (context != null) {
      Properties props = context.getChildrenAsProperties();
      // Check that all settings are known to the configuration class
      MetaClass metaConfig = MetaClass.forClass(Configuration.class);
      for (Object key : props.keySet()) {
        if (!metaConfig.hasSetter(String.valueOf(key))) {
          throw new BuilderException("The setting " + key + " is not known.  Make sure you spelled it correctly (case sensitive).");
        }
      }
      configuration.setAutoMappingBehavior(AutoMappingBehavior.valueOf(props.getProperty("autoMappingBehavior", "PARTIAL")));
      configuration.setCacheEnabled(booleanValueOf(props.getProperty("cacheEnabled"), true));
      configuration.setProxyFactory((ProxyFactory) createInstance(props.getProperty("proxyFactory")));
      configuration.setLazyLoadingEnabled(booleanValueOf(props.getProperty("lazyLoadingEnabled"), false));
      configuration.setAggressiveLazyLoading(booleanValueOf(props.getProperty("aggressiveLazyLoading"), true));
      configuration.setMultipleResultSetsEnabled(booleanValueOf(props.getProperty("multipleResultSetsEnabled"), true));
      configuration.setUseColumnLabel(booleanValueOf(props.getProperty("useColumnLabel"), true));
      configuration.setUseGeneratedKeys(booleanValueOf(props.getProperty("useGeneratedKeys"), false));
      configuration.setDefaultExecutorType(ExecutorType.valueOf(props.getProperty("defaultExecutorType", "SIMPLE")));
      configuration.setDefaultStatementTimeout(integerValueOf(props.getProperty("defaultStatementTimeout"), null));
      configuration.setMapUnderscoreToCamelCase(booleanValueOf(props.getProperty("mapUnderscoreToCamelCase"), false));
      configuration.setSafeRowBoundsEnabled(booleanValueOf(props.getProperty("safeRowBoundsEnabled"), false));
      configuration.setLocalCacheScope(LocalCacheScope.valueOf(props.getProperty("localCacheScope", "SESSION")));
      configuration.setJdbcTypeForNull(JdbcType.valueOf(props.getProperty("jdbcTypeForNull", "OTHER")));
      configuration.setLazyLoadTriggerMethods(stringSetValueOf(props.getProperty("lazyLoadTriggerMethods"), "equals,clone,hashCode,toString"));
      configuration.setSafeResultHandlerEnabled(booleanValueOf(props.getProperty("safeResultHandlerEnabled"), true));
      configuration.setDefaultScriptingLanguage(resolveClass(props.getProperty("defaultScriptingLanguage")));
      configuration.setCallSettersOnNulls(booleanValueOf(props.getProperty("callSettersOnNulls"), false));
      configuration.setLogPrefix(props.getProperty("logPrefix"));
      configuration.setLogImpl(resolveClass(props.getProperty("logImpl")));
      configuration.setConfigurationFactory(resolveClass(props.getProperty("configurationFactory")));
    }
  }
  //环境元素解析
  private void environmentsElement(XNode context) throws Exception {
    if (context != null) {
      if (environment == null) {
        environment = context.getStringAttribute("default");
      }
      for (XNode child : context.getChildren()) {
        String id = child.getStringAttribute("id");
        if (isSpecifiedEnvironment(id)) {
          TransactionFactory txFactory = transactionManagerElement(child.evalNode("transactionManager"));
          DataSourceFactory dsFactory = dataSourceElement(child.evalNode("dataSource"));
          DataSource dataSource = dsFactory.getDataSource();
          Environment.Builder environmentBuilder = new Environment.Builder(id)
              .transactionFactory(txFactory)
              .dataSource(dataSource);
          configuration.setEnvironment(environmentBuilder.build());
        }
      }
    }
  }
  //解析databaseIdProvider MyBatis能够执行不同的语句取决于你提供的数据库供应商。许多数据库供应商的支持是基于databaseId映射
  private void databaseIdProviderElement(XNode context) throws Exception {
    DatabaseIdProvider databaseIdProvider = null;
    if (context != null) {
      String type = context.getStringAttribute("type");
      if ("VENDOR".equals(type)) type = "DB_VENDOR"; // awful patch to keep backward compatibility
      Properties properties = context.getChildrenAsProperties();
      databaseIdProvider = (DatabaseIdProvider) resolveClass(type).newInstance();
      databaseIdProvider.setProperties(properties);
    }
    Environment environment = configuration.getEnvironment();
    if (environment != null && databaseIdProvider != null) {
      String databaseId = databaseIdProvider.getDatabaseId(environment.getDataSource());
      configuration.setDatabaseId(databaseId);
    }
  }
  //事务配置解析，获得事务工厂(JDBC和MANAGED两种)
  private TransactionFactory transactionManagerElement(XNode context) throws Exception {
    if (context != null) {
      String type = context.getStringAttribute("type");
      Properties props = context.getChildrenAsProperties();
      TransactionFactory factory = (TransactionFactory) resolveClass(type).newInstance();
      factory.setProperties(props);
      return factory;
    }
    throw new BuilderException("Environment declaration requires a TransactionFactory.");
  }
  //数据源解析获得数据源工厂
  private DataSourceFactory dataSourceElement(XNode context) throws Exception {
    if (context != null) {
      String type = context.getStringAttribute("type");
      Properties props = context.getChildrenAsProperties();
      DataSourceFactory factory = (DataSourceFactory) resolveClass(type).newInstance();
      factory.setProperties(props);
      return factory;
    }
    throw new BuilderException("Environment declaration requires a DataSourceFactory.");
  }
  //类型控制元素解析，数据库数据类型和Java数据类型的解析
  private void typeHandlerElement(XNode parent) throws Exception {
    if (parent != null) {
      for (XNode child : parent.getChildren()) {
        if ("package".equals(child.getName())) {
          String typeHandlerPackage = child.getStringAttribute("name");
          typeHandlerRegistry.register(typeHandlerPackage);
        } else {
          String javaTypeName = child.getStringAttribute("javaType");
          String jdbcTypeName = child.getStringAttribute("jdbcType");
          String handlerTypeName = child.getStringAttribute("handler");
          Class<?> javaTypeClass = resolveClass(javaTypeName);
          JdbcType jdbcType = resolveJdbcType(jdbcTypeName);
          Class<?> typeHandlerClass = resolveClass(handlerTypeName);
          if (javaTypeClass != null) {
            if (jdbcType == null) {
              typeHandlerRegistry.register(javaTypeClass, typeHandlerClass);
            } else {
              typeHandlerRegistry.register(javaTypeClass, jdbcType, typeHandlerClass);
            }
          } else {
            typeHandlerRegistry.register(typeHandlerClass);
          }
        }
      }
    }
  }
  //mapper元素解析，获得各种crud操作或者配置文件
  private void mapperElement(XNode parent) throws Exception {
    if (parent != null) {
      for (XNode child : parent.getChildren()) {
        if ("package".equals(child.getName())) {
          String mapperPackage = child.getStringAttribute("name");
          configuration.addMappers(mapperPackage);
        } else {
          String resource = child.getStringAttribute("resource");
          String url = child.getStringAttribute("url");
          String mapperClass = child.getStringAttribute("class");
          if (resource != null && url == null && mapperClass == null) {
            ErrorContext.instance().resource(resource);
            InputStream inputStream = Resources.getResourceAsStream(resource);
            XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments());
            mapperParser.parse();
          } else if (resource == null && url != null && mapperClass == null) {
            ErrorContext.instance().resource(url);
            InputStream inputStream = Resources.getUrlAsStream(url);
            XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, url, configuration.getSqlFragments());
            mapperParser.parse();
          } else if (resource == null && url == null && mapperClass != null) {
            Class<?> mapperInterface = Resources.classForName(mapperClass);
            configuration.addMapper(mapperInterface);
          } else {
            throw new BuilderException("A mapper element may only specify a url, resource or class, but not more than one.");
          }
        }
      }
    }
  }

  private boolean isSpecifiedEnvironment(String id) {
    if (environment == null) {
      throw new BuilderException("No environment specified.");
    } else if (id == null) {
      throw new BuilderException("Environment requires an id attribute.");
    } else if (environment.equals(id)) {
      return true;
    }
    return false;
  }

}