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【12.MyBatis源码剖析与架构实战】1.核⼼流程源码剖析

news 2026/4/21 0:14:30

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 SqlSessionFactory

MyBatis 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：Configuration
Configuration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!=null&&url==null&&mapperClass==null){// 资源方式：解析 XML 文件XMLMapperBuildermapperParser=newXMLMapperBuilder(Resources.getResourceAsStream(resource),configuration,resource,configuration.getSqlFragments());mapperParser.parse();}elseif(resource==null&&url!=null&&mapperClass==null){// URL 方式XMLMapperBuildermapperParser=newXMLMapperBuilder(Resources.getUrlAsStream(url),configuration,url,configuration.getSqlFragments());mapperParser.parse();}elseif(resource==null&&url==null&&mapperClass!=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);}}