MyBatis 添加元数据自定义元素标签的实现代码

开发背景

 现有系统中维护了一套业务表相关列、键的元数据，电脑维修网希望通过读取元数据实现自动封装 SQL 语句、自定义主键策略。实现方案为入侵式修改 MyBatis，增加元素标签meta，支持业务开发中可以在XML映射文件中使用。

meta元素设计如下

期望示例如下

 



 



 select 
  
 from USER 
 here  = #{__PK_VALUE}

开发准备

 新建项目并引入 mybatis 、 mybatis-spring 两个核心依赖。

 .mybatis
 mybatis



 .mybatis
 mybatis-spring

增加自定义元素

创建 metaHandler 和 metaSqlNode

public class metaHandler implements NodeHandler {

 private final CustomConfiguration configuration;

 protected metaHandler(CustomConfiguration configuration) {
 this.configuration = configuration;
 }

 @Override
 public void handleNode(XNode nodeToHandle, List targetContents) {
 final String test = nodeToHandle.getStringAttribute("test");
 final String type = nodeToHandle.getStringAttribute("type");
 final String ignore = nodeToHandle.getStringAttribute("ignore");
 final String table = nodeToHandle.getStringAttribute("table");
 final String func = nodeToHandle.getStringAttribute("func");
 String alias = nodeToHandle.getStringAttribute("alias");
 if (!StringUtils.isEmpty(alias)) {
  alias = alias.trim();
  //是否无效 防止注入
  boolean invalid = alias.contains(" ") || alias.contains(".");
  if (invalid) {
  thro ne RuntimeException("alias is invalid : " + alias);
  }
 }
 metaSqlNode metaSqlNode = ne metaSqlNode(configuration, test, type, ignore, table, func, alias);
 targetContents.add(metaSqlNode);
 }
}

public class metaSqlNode implements SqlNode {

 
 private final CustomConfiguration configuration;
 
 private final expressionevaluator evaluator;
 
 private final String test;
 
 private final TypeEnum type;
 
 private final String ignore;
 
 private final String table;
 
 private final String func;
 
 private final String alias;

 public metaSqlNode(CustomConfiguration configuration, String test, String type, String ignore, String table, String func, String alias) {
 this.evaluator = ne expressionevaluator();
 this.configuration = configuration;
 this.test = test;
 this.type = TypeEnum.parse(type);
 this.ignore = ignore;
 this.table = table;
 this.func = func;
 this.alias = alias;
 }

 @Override
 public boolean apply(DynamicContext context) {
 // TODO 解析type与table，向context中添加语句
 context.appendSql(" insert ······ ");
 }
}

创建 CustomXMLscriptBuilder

 内容复制自.apache.ibatis.scripting.xmltags.XMLscriptBuilder，在 initNodeHandlerMap 方法中添加 metaHandler。

private void initNodeHandlerMap() {
 nodeHandlerMap.put("trim", ne TrimHandler());
 nodeHandlerMap.put("here", ne WhereHandler());
 nodeHandlerMap.put("set", ne SetHandler());
 nodeHandlerMap.put("foreach", ne ForEachHandler());
 nodeHandlerMap.put("if", ne IfHandler());
 nodeHandlerMap.put("choose", ne ChooseHandler());
 nodeHandlerMap.put("hen", ne IfHandler());
 nodeHandlerMap.put("otherise", ne OtheriseHandler());
 nodeHandlerMap.put("bind", ne BindHandler());
 //增加元数据标签解析器
 if (configuration instanceof CustomConfiguration) {
 nodeHandlerMap.put("meta", ne metaHandler((CustomConfiguration) configuration));
 }
}

创建 CustomXMLLanguageDriver

 内容复制自.apache.ibatis.scripting.xmltags.XMLLanguageDriver，在 createSqlSource 方法中使用 CustomXMLscriptBuilder 来解析Xml生成 SqlSource。

@Override
public SqlSource createSqlSource(Configuration configuration, XNode script, Class parameterType) {
 CustomXMLscriptBuilder builder = ne CustomXMLscriptBuilder(configuration, script, parameterType);
 return builder.parsescriptNode();
}

创建 CustomConfiguration

 继承.apache.ibatis.session.Configuration，内容复制自 Configuration。将构造方法中的 XMLLanguageDriver 修改为 CustomConfiguration。

public CustomConfiguration() {
 
 ······
 
 //默认使用自定义 LanguageDriver
 typeAliasRegistry.registerAlias("XML", CustomXMLLanguageDriver.class);
 
 ······
 
 //默认使用自定义 LanguageDriver
 languageRegistry.setDefaultDriverClass(CustomXMLLanguageDriver.class);
 
 ······
 
}

创建 CustomXMLConfigBuilder

 内容复制自.apache.ibatis.builder.xml.XMLConfigBuilder，支持通过 XML 配置来创建 CustomConfiguration。

public class CustomXMLConfigBuilder extends baseBuilder {
 
 ······
 
 private CustomXMLConfigBuilder(XPathParser parser, String environment, Properties props) {
 // 使用 CustomConfiguration
 super(ne CustomConfiguration());
 ErrorContext.instance().resource("SQL Mapper Configuration");
 this.configuration.setVariables(props);
 this.parsed = false;
 this.environment = environment;
 this.parser = parser;
 }
 
 ······
 
}

创建 SqlSessionFactory

 复制自.mybatis.spring.SqlSessionFactoryBean，将 buildSqlSessionFactory 方法中的 Configuration 替换为 CustomConfiguration。

protected SqlSessionFactory buildSqlSessionFactory() thros Exception {

 final Configuration targetConfiguration;

 CustomXMLConfigBuilder xmlConfigBuilder = null;
 if (this.configuration != null) {
 targetConfiguration = this.configuration;
 if (targetConfiguration.getVariables() == null) {
  targetConfiguration.setVariables(this.configurationProperties);
 } else if (this.configurationProperties != null) {
  targetConfiguration.getVariables().putAll(this.configurationProperties);
 }
 } else if (this.configLocation != null) {
 // 使用 CustomXMLConfigBuilder 创建 CustomConfiguration
 xmlConfigBuilder = ne CustomXMLConfigBuilder(this.configLocation.getInputStream(), null, this.configurationProperties);
 targetConfiguration = xmlConfigBuilder.getConfiguration();
 } else {
 LOGGER.debug(
  () -> "Property 'configuration' or 'configLocation' not specified, using default MyBatis Configuration");
 // 使用 CustomConfiguration
 targetConfiguration = ne CustomConfiguration();
 Optional.ofNullable(this.configurationProperties).ifPresent(targetConfiguration::setVariables);
 }
 
 ······
 
 return this.sqlSessionFactoryBuilder.build(targetConfiguration);
}

修改DTD约束

 MyBatis 的约束文件并不支持自定义的 meta 元素，需要使用 CDATA 来处理。示例如下

 
 ]]>

 如果不想要 CDATA，则需要通过修改DTD约束来完成。

• 在 classes 下指定位置添加DTD约束文件/apache/ibatis/builder/xml/mybatis-3-config.dtd达到覆盖 MyBatis DTD的效果。
• 重写代码来使用指定 DTD 。

创建 CustomXMLMapperEntityResolver

 复制自.apache.ibatis.builder.xml.XMLMapperEntityResolver，将MYBATIS_MAPPER_DTD修改为指向本地 mybatis-3-mapper.dtd 文件，并在DTD文件中添加 meta 元素的约束。

public class CustomXMLMapperEntityResolver implements EntityResolver {
 
 ······
 
 private static final String MYBATIS_MAPPER_DTD = "/my/ibatis/builder/xml/mybatis-3-mapper.dtd";
 
 ······
 
}

CustomXMLLanguageDriver

  Mapper动态语句注解处理使用 CustomXMLMapperEntityResolver。

@Override
public SqlSource createSqlSource(Configuration configuration, String script, Class parameterType) {
 // issue #3
 if (script.startsWith("