mybatis-初始化(一)mybatis-confg解析

概述

mybatis初始化主要包含mybatis全局配置加载、解析，mapper文件加载解析。本篇主要是对mybatis配置文件解析进行解读。

先看下mybatis-config.xml有些啥内容

configuration（配置）
- properties（属性）
- settings（设置）
- typeAliases（类型别名）
- typeHandlers（类型处理器）
- objectFactory（对象工厂）
- plugins（插件）
- environments（环境配置）
  - environment（环境变量）
    - transactionManager（事务管理器）
    - dataSource（数据源）
- databaseIdProvider（数据库厂商标识）
- mappers（映射器）

每节对应一个xml node。开干！

解析入口

public SqlSessionFactory build(Reader reader, String environment, Properties properties) {
  try {
    XMLConfigBuilder parser = new XMLConfigBuilder(reader, environment, properties);
    /*
     * 1. 执行xml解析
     * 2. 解析后的config，创建SqlSessionFactory
     */
    return build(parser.parse());
  } catch (Exception e) {
    throw ExceptionFactory.wrapException("Error building SqlSession.", e);
  } finally {
    ErrorContext.instance().reset();
    try {
      reader.close();
    } catch (IOException e) {
      // Intentionally ignore. Prefer previous error.
    }
  }
}

在SqlSessionFactoryBuilder.build()中，解析完Configuration直接创建SqlSessionFactory。

configuration解析

mybatis-config.xml的输入流已经在XPathParser里了。

public class XMLConfigBuilder extends BaseBuilder {

  /**
   * 是否已经解析
   */
  private boolean parsed;

  /**
   * Xpath解析器
   */
  private final XPathParser parser;

  /**
   * 当前应用的环境id
   */
  private String environment;
  
    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;
  }
}

xml配置构造器存储XPath解析器，主要用它来完成xml相关的解析。

解析方法如下：

public Configuration parse() {
  if (parsed) {
    throw new BuilderException("Each XMLConfigBuilder can only be used once.");
  }
  parsed = true;

  //解析 configuration节点，configuration是根节点
  parseConfiguration(parser.evalNode("/configuration"));
  return configuration;
}

/**
 * 解析config.xml
 * @param root
 */
private void parseConfiguration(XNode root) {
  try {
    // 解析<properties/>
    propertiesElement(root.evalNode("properties"));

    // 解析<settings />
    Properties settings = settingsAsProperties(root.evalNode("settings"));
    // vfs实现类处理
    loadCustomVfs(settings);
    // 日志实现类处理
    loadCustomLogImpl(settings);

    // 解析<typeAliases />
    typeAliasesElement(root.evalNode("typeAliases"));

    // 解析<plugins />
    pluginElement(root.evalNode("plugins"));

    // 解析<objectFactory />
    objectFactoryElement(root.evalNode("objectFactory"));

    // 解析<objectWrapperFactory />
    objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));

    // 解析<reflectorFactory />
    reflectorFactoryElement(root.evalNode("reflectorFactory"));

    // Configuration属性设置
    settingsElement(settings);

    // 解析<environments />
    environmentsElement(root.evalNode("environments"));

    // 解析<databaseIdProvider />
    databaseIdProviderElement(root.evalNode("databaseIdProvider"));

    // 解析<typeHandlers />
    typeHandlerElement(root.evalNode("typeHandlers"));

    // 解析<mappers />
    mapperElement(root.evalNode("mappers"));
  } catch (Exception e) {
    throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
  }
}

从上到下按照针对每个子xml node挨个解析，很清晰。

让我们挨个看，重要的重点看，不重要的扫一眼。

properties解析

properties主要是为了解决占位符替换（${}），可以自定义变量，也可以外部引入。涉及到xml相关的知识不展开，主要是把解析好的properties存储到parser和Configuration中，后续使用。

private void propertiesElement(XNode context) throws Exception {
  if (context != null) {
    //直接使用XNode提供的方法，将node解析成Properties
    Properties defaults = context.getChildrenAsProperties();

    // 引用外部properties解析支持
    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);
    }

    // 将解析好的 properties放到解析器中，进行后续动态值替换
    parser.setVariables(defaults);
    configuration.setVariables(defaults);
  }
}

settings解析

settings也当做properties处理。只看下解析逻辑，具体每个配置有什么作用，可以去官网参考下。

<settings>
  <setting name="cacheEnabled" value="true"/>
  <setting name="lazyLoadingEnabled" value="true"/>
  <setting name="multipleResultSetsEnabled" value="true"/>
  <setting name="useColumnLabel" value="true"/>
  <setting name="useGeneratedKeys" value="false"/>
  <setting name="autoMappingBehavior" value="PARTIAL"/>
  <setting name="autoMappingUnknownColumnBehavior" value="WARNING"/>
  <setting name="defaultExecutorType" value="SIMPLE"/>
  <setting name="defaultStatementTimeout" value="25"/>
  <setting name="defaultFetchSize" value="100"/>
  <setting name="safeRowBoundsEnabled" value="false"/>
  <setting name="mapUnderscoreToCamelCase" value="false"/>
  <setting name="localCacheScope" value="SESSION"/>
  <setting name="jdbcTypeForNull" value="OTHER"/>
  <setting name="lazyLoadTriggerMethods" value="equals,clone,hashCode,toString"/>
</settings>

private Properties settingsAsProperties(XNode context) {
  if (context == null) {
    return new Properties();
  }

  // 将settings转换成properties
  Properties props = context.getChildrenAsProperties();
  // Check that all settings are known to the configuration class
  MetaClass metaConfig = MetaClass.forClass(Configuration.class, localReflectorFactory);

  // 遍历通过setter方法判断是否存在非法属性
  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).");
    }
  }
  return props;
}

TypeAlias解析

逻辑较简单，具体别名处理在type中的alias已经讲过了

private void typeAliasesElement(XNode parent) {
  if (parent != null) {
    for (XNode child : parent.getChildren()) {
      // 大多数情况使用指定package的方式
      if ("package".equals(child.getName())) {
        String typeAliasPackage = child.getStringAttribute("name");
        // 通过typeAliasRegistry提供的批量注册功能，注册该包下的所有类
        configuration.getTypeAliasRegistry().registerAliases(typeAliasPackage);
      } else {
        //单个的处理
        String alias = child.getStringAttribute("alias");
        String type = child.getStringAttribute("type");
        try {
          Class<?> clazz = Resources.classForName(type);
          if (alias == null) {
            typeAliasRegistry.registerAlias(clazz);
          } else {
            typeAliasRegistry.registerAlias(alias, clazz);
          }
        } catch (ClassNotFoundException e) {
          throw new BuilderException("Error registering typeAlias for '" + alias + "'. Cause: " + e, e);
        }
      }
    }
  }

plugins解析

这里先了解下插件是如何解析和注册的。插件的具体内容将在mybatis整体介绍完之后再讲解。

private void pluginElement(XNode parent) throws Exception {
  if (parent != null) {
    for (XNode child : parent.getChildren()) {
      String interceptor = child.getStringAttribute("interceptor");
      Properties properties = child.getChildrenAsProperties();
      // 通过 别名 解析出类型，使用默认构造函数创建实例
      Interceptor interceptorInstance = (Interceptor) resolveClass(interceptor).getDeclaredConstructor().newInstance();
      // 设置属性值
      interceptorInstance.setProperties(properties);
      // 添加拦截器
      configuration.addInterceptor(interceptorInstance);
    }
  }
}

对象工厂

支持指定对象工厂，可以自定义对象创建过程，就是入参、出参。

private void objectFactoryElement(XNode context) throws Exception {
  if (context != null) {
    String type = context.getStringAttribute("type");
    Properties properties = context.getChildrenAsProperties();
    // 别名 解析类型，创建实例
    ObjectFactory factory = (ObjectFactory) resolveClass(type).getDeclaredConstructor().newInstance();
    // 设置属性
    factory.setProperties(properties);
    // 添加Object工厂
    configuration.setObjectFactory(factory);
  }
}

对象包装器工厂

用的少，略过

private void objectWrapperFactoryElement(XNode context) throws Exception {
  if (context != null) {
    String type = context.getStringAttribute("type");
    ObjectWrapperFactory factory = (ObjectWrapperFactory) resolveClass(type).getDeclaredConstructor().newInstance();
    configuration.setObjectWrapperFactory(factory);
  }
}

反射器工厂

用的少，略过

private void reflectorFactoryElement(XNode context) throws Exception {
  if (context != null) {
    String type = context.getStringAttribute("type");
    ReflectorFactory factory = (ReflectorFactory) resolveClass(type).getDeclaredConstructor().newInstance();
    configuration.setReflectorFactory(factory);
  }
}

默认配置

默认配置设置

private void settingsElement(Properties props) {
  configuration.setAutoMappingBehavior(AutoMappingBehavior.valueOf(props.getProperty("autoMappingBehavior", "PARTIAL")));
  configuration.setAutoMappingUnknownColumnBehavior(AutoMappingUnknownColumnBehavior.valueOf(props.getProperty("autoMappingUnknownColumnBehavior", "NONE")));
  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"), false));
  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.setDefaultFetchSize(integerValueOf(props.getProperty("defaultFetchSize"), null));
  configuration.setDefaultResultSetType(resolveResultSetType(props.getProperty("defaultResultSetType")));
  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.setDefaultEnumTypeHandler(resolveClass(props.getProperty("defaultEnumTypeHandler")));
  configuration.setCallSettersOnNulls(booleanValueOf(props.getProperty("callSettersOnNulls"), false));
  configuration.setUseActualParamName(booleanValueOf(props.getProperty("useActualParamName"), true));
  configuration.setReturnInstanceForEmptyRow(booleanValueOf(props.getProperty("returnInstanceForEmptyRow"), false));
  configuration.setLogPrefix(props.getProperty("logPrefix"));
  configuration.setConfigurationFactory(resolveClass(props.getProperty("configurationFactory")));
}

环境信息解析

<environments default="development">
  <environment id="development">
    <transactionManager type="JDBC">
      <property name="..." value="..."/>
    </transactionManager>
    <dataSource type="POOLED">
      <property name="driver" value="${driver}"/>
      <property name="url" value="${url}"/>
      <property name="username" value="${username}"/>
      <property name="password" value="${password}"/>
    </dataSource>
  </environment>
</environments>

多环境一般不使用mybatis的多environment配置，所以用的少。

private void environmentsElement(XNode context) throws Exception {
  if (context != null) {
    // 如果未指定，则解析标签上的默认
    if (environment == null) {
      environment = context.getStringAttribute("default");
    }
    for (XNode child : context.getChildren()) {
      String id = child.getStringAttribute("id");

      // 如果是当前应用的环境才会进行设置和添加
      if (isSpecifiedEnvironment(id)) {

        // 解析<transactionManager />标签
        TransactionFactory txFactory = transactionManagerElement(child.evalNode("transactionManager"));
        // 解析<dataSource />标签
        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());
      }
    }
  }
}

数据库厂商id解析

用的少，略过

private void databaseIdProviderElement(XNode context) throws Exception {
  DatabaseIdProvider databaseIdProvider = null;
  if (context != null) {
    String type = context.getStringAttribute("type");
    // awful patch to keep backward compatibility
    if ("VENDOR".equals(type)) {
      type = "DB_VENDOR";
    }
    Properties properties = context.getChildrenAsProperties();
    databaseIdProvider = (DatabaseIdProvider) resolveClass(type).getDeclaredConstructor().newInstance();
    databaseIdProvider.setProperties(properties);
  }
  Environment environment = configuration.getEnvironment();
  if (environment != null && databaseIdProvider != null) {
    String databaseId = databaseIdProvider.getDatabaseId(environment.getDataSource());
    configuration.setDatabaseId(databaseId);
  }
}

类型处理器解析

即可指定包名批量注册，又可以单个注册。

private void typeHandlerElement(XNode parent) {
  if (parent != null) {
    for (XNode child : parent.getChildren()) {
      if ("package".equals(child.getName())) {
        String typeHandlerPackage = child.getStringAttribute("name");
        // 通过包名批量注册typeHandler
        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映射文件解析

重点，mapper映射文件就是我们写sql的文件。解析映射文件，然后和Mapper接口建立映射。

看下mapper的配置内容实例：

<!-- 使用相对于类路径的资源引用 -->
<mappers>
  <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
  <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
  <mapper resource="org/mybatis/builder/PostMapper.xml"/>
</mappers>
<!-- 使用完全限定资源定位符（URL） -->
<mappers>
  <mapper url="file:///var/mappers/AuthorMapper.xml"/>
  <mapper url="file:///var/mappers/BlogMapper.xml"/>
  <mapper url="file:///var/mappers/PostMapper.xml"/>
</mappers>
<!-- 使用映射器接口实现类的完全限定类名 -->
<mappers>
  <mapper class="org.mybatis.builder.AuthorMapper"/>
  <mapper class="org.mybatis.builder.BlogMapper"/>
  <mapper class="org.mybatis.builder.PostMapper"/>
</mappers>
<!-- 将包内的映射器接口实现全部注册为映射器 -->
<mappers>
  <package name="org.mybatis.builder"/>
</mappers>

共有4中方式配置mapper.xml，看下代码如何解析

private void mapperElement(XNode parent) throws Exception {
  if (parent != null) {
    for (XNode child : parent.getChildren()) {
      if ("package".equals(child.getName())) {
        // 通过包名批量注册
        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) {
          // 通过resource外部引入的需要单独解析
          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) {
          // 通过url外部引入的需要单独解析
          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) {
          // 通过Mapper接口的相同路径尝试加载
          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.");
        }
      }
    }
  }
}

这里分两种情况，

一：配置的是Mapper Class，包名和class，是先去加载mapper接口，然后再当前路径将.java替换成.xml尝试加载。

二：直接配置的Mapper.xml，那么委托给XMLMapperBuilder进行具体内容解析。

Mapper.xml的内容具体比较复杂，单独放在一篇文章进行解析。

总结

mybatis-config的解析比较简单，只要可以对着官网的文档，先看配置的内容和格式，再看代码如何解析，按部就班看几眼就能懂。

mybatis-初始化(一)mybatis-confg解析

概述

解析入口

configuration解析

properties解析

settings解析

TypeAlias解析

plugins解析

对象工厂

对象包装器工厂

反射器工厂

默认配置

环境信息解析

数据库厂商id解析

类型处理器解析

mapper映射文件解析

总结

mybatis-reflection反射包解析

mybatis-binding 綁定包解析

mybatis-初始化(三)statement解析

mybatis-cache緩存包解析

mybatis-初始化(二)映射文件解析

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