下面说说Mybatis的动态Sql的SqlSource构造SqlSource对象。当Mapper.xml的每一个标签被解析后，SqlNode就会被SqlSourceBuilder进一步处理。publicSqlSourceparse(StringoriginalSql,ClassparameterType,MapadditionalParameters){ParameterMappingTokenHandlerhandler=newParameterMappingTokenHandler(configuration,parameterType,additionalParameters);GenericTokenParser解析器=newGenericTokenParser("#{","}",handler);字符串sql;如果（配置。（originalSql））；}else{sql=parser.parse(originalSql);}returnnewStaticSqlSource(configuration,sql,handler.getParameterMappings());}1.ParameterMappingTokenHandler是一个静态内部类，用来保存各个占位符2.创建一个识别#{}占位符的GenericTokenParser，解析sql，最后形成一个StaticSqlSource对象。SqlSource接口。SqlSource接口用于创建由数据库执行的sql。它只有一个getBoundSql()方法publicinterfaceSqlSource{BoundSqlgetBoundSql(ObjectparameterObject);}有DynamicSqlSource、StaticSqlSource、RawSqlSource、ProviderSqlSource、VelocitySqlSource，这里重点说一下前三个实例动态Sql类DynamicSqlSource是解析动态sql的类publicclassprivatefinalfinalDynamicSqlSourceimplementsConfiguration;私有最终SqlNoderootSqlNode；publicDynamicSqlSource(Configurationconfiguration,SqlNoderootSqlNode){this.configuration=configuration;this.rootSqlNode=rootSqlNode;}@OverridepublicBoundSqlgetBoundSql(ObjectparameterObject){DynamicContextcontext=newDynamicContext(configuration,parameterObject);rootSqlNode.apply（上下文）；SqlSourceBuildersqlSourceParser=newSqlSourceBuilder(配置);类parameterType=parameterObject==null?Object.class:parameterObject.getClass();SqlSourcesqlSource=sqlSourceParser.parse(context.getSql(),parameterType,context.getBindings());BoundSqlboundSql=sqlSource.getBoundSql(parameterObject);context.getBindings().forEach(boundSql::setAdditionalParameter);返回绑定SQL；}}在其getBoundSql()方法中：创建一个DynamicContext对象，调用SqlNode的apply()方法完成sql片段的解析创建一个SqlSourceBuilder对象，调用parse()方法解析#{}，替换为?Placeholder，返回StaticSqlSource对象，调用StaticSqlSource的getBoundSql()方法，返回BoundSql对象，其中存放了sql语句的相关信息，返回BoundSql对象解析静态SQL类RawSqlSource用于解析静态sql文件，解析当程序启动时publicclassRawSqlSourceimplementsSqlSource{privatefinalSqlSourcesqlSource;publicRawSqlSource(Configurationconfiguration,SqlNoderootSqlNode,ClassparameterType){this(configuration,getSql(configuration,rootSqlNode),parameterSqlTypeconfig);}publicsql,ClassparameterType){SqlSourceBuildersqlSourceParser=newSqlSourceBuilder(configuration);类clazz=parameterType==null?对象类：参数类型；sqlSource=sqlSourceParser.parse(sql,clazz,newHashMap<>());}privatestaticStringgetSql(Configurationconfiguration,SqlNoderootSqlNode){DynamicContextcontext=newDynamicContext(configuration,null);rootSqlNode.apply（上下文）；返回context.getSql();}@OverridepublicBoundSqlgetBoundSql(ObjectparameterObject){returnsqlSource.getBoundSql(parameterObject);}}它的构造方法调用getSql()方法。该方法中调用SqlSource的apply()方法拼装出完整的sql，然后调用parse()方法通过SqlSourceBuilder处理#{}占位符，返回StaticSqlSource对象。StaticSqlSourceStaticSqlSource类：publicclassStaticSqlSourceimplementsSqlSource{@OverridepublicBoundSqlgetBoundSql(ObjectparameterObject){returnnewBoundSql(configuration,sql,parameterMappings,parameterObject);}}它的getBoundSql()方法是创建一个BoundSql对象总结本文讲了SqlSource的接口和它的几个实现类，其中DynamicSqlSource类和RawSqlSource类最后生成了StaticSqlSource类，getBoundSql()方法由StaticSqlSource类调用以创建BoundSql类。DynamicSqlSource是解析动态SQL的类，RawSqlSource是解析静态SQL的类。程序启动时会生成sql。欢迎关注我的公众号：打码老贾回复“领取”送《Java面试》信息，阿里、腾讯、字节、美团、饿了么等大厂
