【12.MyBatis源码剖析与架构实战】1.核⼼流程源码剖析

MyBatis 核心流程源码剖析MyBatis 作为一款优秀的持久层框架，通过封装 JDBC 的繁杂操作，让开发者只需专注于 SQL 本身。其核心流程分为两大阶段：初始化阶段（构建SqlSessionFactory）和执行阶段（通过SqlSession执行 SQL）。以下将结合源码对这两个阶段进行深度剖析。一、初始化阶段：构建 SqlSessionFactoryMyBatis 的初始入口是SqlSessionFactoryBuilder，它负责解析配置文件并构建SqlSessionFactory。1.1 SqlSessionFactoryBuilder.build() 入口// SqlSessionFactoryBuilder.javapublicSqlSessionFactorybuild(InputStreaminputStream,Stringenvironment,Propertiesproperties){try{// 创建 XMLConfigBuilder，用于解析 mybatis-config.xmlXMLConfigBuilderparser=newXMLConfigBuilder(inputStream,environment,properties);// 解析配置文件，生成 Configuration 对象Configurationconfiguration=parser.parse();// 构建 DefaultSqlSessionFactoryreturnbuild(configuration);}catch(Exceptione){throwExceptionFactory.wrapException("Error building SqlSession.",e);}finally{// 关闭输入流try{inputStream.close();}catch(IOExceptione){// ignore}}}1.2 XMLConfigBuilder 解析配置文件XMLConfigBuilder使用 XPath 解析 MyBatis 的核心配置文件，解析顺序如下：properties→settings→typeAliases→typeHandlers→objectFactory→objectWrapperFactory→reflectorFactory→plugins→environments→databaseIdProvider→mappers。// XMLConfigBuilder.parse()publicConfigurationparse(){if(parsed){thrownewBuilderException("Each XMLConfigBuilder can only be used once.");}parsed=true;// 解析 configuration 节点parseConfiguration(parser.evalNode("/configuration"));returnconfiguration;}privatevoidparseConfiguration(XNoderoot){try{propertiesElement(root.evalNode("properties"));Propertiessettings=settingsAsProperties(root.evalNode("settings"));loadCustomVfs(settings);typeAliasesElement(root.evalNode("typeAliases"));pluginElement(root.evalNode("plugins"));objectFactoryElement(root.evalNode("objectFactory"));objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));reflectorFactoryElement(root.evalNode("reflectorFactory"));settingsElement(settings);environmentsElement(root.evalNode("environments"));databaseIdProviderElement(root.evalNode("databaseIdProvider"));typeHandlerElement(root.evalNode("typeHandlers"));mapperElement(root.evalNode("mappers"));}catch(Exceptione){thrownewBuilderException("Error parsing SQL Mapper Configuration. Cause: "+e,e);}}核心对象：ConfigurationConfiguration是 MyBatis 中最重要的“容器类”，贯穿整个生命周期，存储了所有配置信息、Mapper 映射、类型处理器、插件等信息。1.3 解析 Mapper 文件mapperElement方法负责解析 Mapper 文件或注解接口：// XMLConfigBuilder.mapperElement()privatevoidmapperElement(XNodeparent)throwsException{if(parent!=null){for(XNodechild:parent.getChildren()){if("package".equals(child.getName())){// 扫描包方式StringmapperPackage=child.getStringAttribute("name");configuration.addMappers(mapperPackage);}else{Stringresource=child.getStringAttribute("resource");Stringurl=child.getStringAttribute("url");StringmapperClass=child.getStringAttribute("class");if(resource!=nullurl==nullmapperClass==null){// 资源方式：解析 XML 文件XMLMapperBuildermapperParser=newXMLMapperBuilder(Resources.getResourceAsStream(resource),configuration,resource,configuration.getSqlFragments());mapperParser.parse();}elseif(resource==nullurl!=nullmapperClass==null){// URL 方式XMLMapperBuildermapperParser=newXMLMapperBuilder(Resources.getUrlAsStream(url),configuration,url,configuration.getSqlFragments());mapperParser.parse();}elseif(resource==nullurl==nullmapperClass!=null){// 接口方式Class?mapperInterface=Resources.classForName(mapperClass);configuration.addMapper(mapperInterface);}}}}}XMLMapperBuilder在解析 Mapper 文件时，会进一步解析 SQL 语句并构建MappedStatement：// XMLMapperBuilder.configurationElement()privatevoidconfigurationElement(XNodecontext){try{Stringnamespace=context.getStringAttribute("namespace");builderAssistant.setCurrentNamespace(namespace);cacheRefElement(context.evalNode("cache-ref"));cacheElement(context.evalNode("cache"));parameterMapElement(context.evalNodes("/mapper/parameterMap"));resultMapElement(context.evalNodes("/mapper/resultMap"));sqlElement(context.evalNodes("/mapper/sql"));// 解析 select | insert | update | delete 语句buildStatementFromContext(context.evalNodes("select|insert|update|delete"));}catch(Exceptione){thrownewBuilderException("Error parsing Mapper XML. Cause: "+e,e);}}二、SQL 执行流程SQL 执行的入口是SqlSession的 API 调用，核心组件分工明确：SqlSession→Executor→StatementHandler→ParameterHandler→ResultSetHandler。2.1 整体执行流程图数据库交互层核心执行层业务层是未命中否命中未命中