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，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：

<!-- meta标签 可根据参数获取到对应的表名 动态生成语句 -->
<!ELEMENT meta EMPTY>
<!ATTLIST meta
test CDATA #IMPLIED
type (update|insert|select|columns|pk-col|load|load-columns) #IMPLIED
ignore CDATA #IMPLIED
table CDATA #IMPLIED
func CDATA #IMPLIED
alias CDATA #IMPLIED
>

期望示例如下：

<insert id="insertMap" useGeneratedKeys="true" generator="meta">
 <meta table="USER" type="insert"/>
</insert>

<update id="updateMap">
 <meta table="USER" type="update"/>
</update>

<select id="selectOneByPk" resultType="java.util.HashMap">
 select
 <meta table="USER" type="columns"/>
 from USER
 where <meta table="USER" type="pk-col"/> = #{__PK_VALUE}
</select>

开发准备

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

<!-- mybatis -->
<dependency>
 <groupId>org.mybatis</groupId>
 <artifactId>mybatis</artifactId>
</dependency>
<!-- mybatis-spring -->
<dependency>
 <groupId>org.mybatis</groupId>
 <artifactId>mybatis-spring</artifactId>
</dependency>

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<SqlNode> 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) {
    throw new RuntimeException("alias is invalid : " + alias);
   }
  }
  MetaSqlNode metaSqlNode = new MetaSqlNode(configuration, test, type, ignore, table, func, alias);
  targetContents.add(metaSqlNode);
 }
}

public class MetaSqlNode implements SqlNode {

 /**
  * mybatis核心数据
  */
 private final CustomConfiguration configuration;
 /**
  * 判断语句校验器
  */
 private final ExpressionEvaluator evaluator;
 /**
  * 判断语句,同if标签
  */
 private final String test;
 /**
  * 生成语句类型 update|insert|select|columns|pk-col|load|load-columns
  */
 private final TypeEnum type;
 /**
  * 忽略的列
  */
 private final String ignore;
 /**
  * 表名，未指定则从调用参数中获取
  */
 private final String table;
 /**
  * 功能，未指定则从调用参数中获取
  */
 private final String func;
 /**
  * 动态列别名
  */
 private final String alias;

 public MetaSqlNode(CustomConfiguration configuration, String test, String type, String ignore, String table, String func, String alias) {
  this.evaluator = new 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org.apache.ibatis.scripting.xmltags.XMLScriptBuilder，在 initNodeHandlerMap 方法中添加 MetaHandler。

private void initNodeHandlerMap() {
 nodeHandlerMap.put("trim", new TrimHandler());
 nodeHandlerMap.put("where", new WhereHandler());
 nodeHandlerMap.put("set", new SetHandler());
 nodeHandlerMap.put("foreach", new ForEachHandler());
 nodeHandlerMap.put("if", new IfHandler());
 nodeHandlerMap.put("choose", new ChooseHandler());
 nodeHandlerMap.put("when", new IfHandler());
 nodeHandlerMap.put("otherwise", new OtherwiseHandler());
 nodeHandlerMap.put("bind", new BindHandler());
 //增加元数据标签解析器
 if (configuration instanceof CustomConfiguration) {
  nodeHandlerMap.put("meta", new MetaHandler((CustomConfiguration) configuration));
 }
}

创建 CustomXMLLanguageDriver

 内容复制自org.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 = new CustomXMLScriptBuilder(configuration, script, parameterType);
 return builder.parseScriptNode();
}

创建 CustomConfiguration

 继承org.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org.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(new 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org.mybatis.spring.SqlSessionFactoryBean，将 buildSqlSessionFactory 方法中的 Configuration 替换为 CustomConfiguration。

protected SqlSessionFactory buildSqlSessionFactory() throws 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 = new 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 = new 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：

<insert id="insertMap" useGeneratedKeys="true" generator="meta">
 <![CDATA[[
 <meta table="USER" type="insert"/>
 ]]>
</insert>

 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org/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org.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 = "com/my/ibatis/builder/xml/mybatis-3-mapper.dtd";

 ······

}

<!-- meta标签 可根据参数获取到对应的表名 动态生成语句 -->
<!ELEMENT meta EMPTY>
<!ATTLIST meta
test CDATA #IMPLIED
type (update|insert|select|columns|pk-col|load|load-columns) #IMPLIED
ignore CDATA #IMPLIED
table CDATA #IMPLIED
func CDATA #IMPLIED
alias CDATA #IMPLIED
>

CustomXMLLanguageDriver

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

/**
 * Mapper动态语句注解调用
 * <p>
 * "<script>select * from user <if test=\"id !=null \">where id = #{id} </if></script>"
 *
 * @param configuration mybatis配置
 * @param script  动态语句字符串
 * @param parameterType 参数类型
 * @return org.apache.ibatis.mapping.SqlSource
 */
@Override
public SqlSource createSqlSource(Configuration configuration, String script, Class<?> parameterType) {
 // issue #3
 if (script.startsWith("<script>")) {
  //将动态语句字符串转换为XNode对象
  XPathParser parser = new XPathParser(script, false, configuration.getVariables(), new CustomXMLMapperEntityResolver());
  return createSqlSource(configuration, parser.evalNode("/script"), parameterType);
 } else {
  // issue #127
  script = PropertyParser.parse(script, configuration.getVariables());
  TextSqlNode textSqlNode = new TextSqlNode(script);
  if (textSqlNode.isDynamic()) {
   return new CustomDynamicSqlSource(configuration, textSqlNode);
  } else {
   return new RawSqlSource(configuration, script, parameterType);
  }
 }
}

创建 CustomXMLMapperBuilder

  复制自org.apache.ibatis.builder.xml.XMLMapperBuilder，修改构造函数使用 CustomXMLMapperEntityResolver 解析xml。

public CustomXMLMapperBuilder(InputStream inputStream, Configuration configuration, String resource, Map<String, XNode> sqlFragments) {
 this(new XPathParser(inputStream, true, configuration.getVariables(), new CustomXMLMapperEntityResolver()),
   configuration, resource, sqlFragments);
}

SqlSessionFactory

 修改 buildSqlSessionFactory 方法，使用 CustomXMLMapperBuilder 来解析xml。

protected SqlSessionFactory buildSqlSessionFactory() throws Exception {

 ······
  try {
   //使用自定义 XMLMapperBuilder
   CustomXMLMapperBuilder xmlMapperBuilder = new CustomXMLMapperBuilder(mapperLocation.getInputStream(),
     targetConfiguration, mapperLocation.toString(), targetConfiguration.getSqlFragments());
   xmlMapperBuilder.parse();
  } catch (Exception e) {
   throw new NestedIOException("Failed to parse mapping resource: '" + mapperLocation + "'", e);
  } finally {
   ErrorContext.instance().reset();
  }

 ······

}

创建 CustomMapperAnnotationBuilder

 复制自org.apache.ibatis.builder.annotation.MapperAnnotationBuilder，修改 loadXmlResource 方法使用 CustomXMLMapperBuilder。

private void loadXmlResource() {
  if (!configuration.isResourceLoaded("namespace:" + type.getName())) {

  ······

    if (inputStream != null) {
      //使用自定义解析器支持自定义标签
      CustomXMLMapperBuilder xmlParser = new CustomXMLMapperBuilder(inputStream, assistant.getConfiguration(), xmlResource, configuration.getSqlFragments(), type.getName());
      xmlParser.parse();
    }
  }
}

创建 CustomMapperRegistry

  复制自org.apache.ibatis.binding.MapperRegistry，修改 addMapper 方法使用 CustomMapperAnnotationBuilder。

@Override
public <T> void addMapper(Class<T> type) {
  if (type.isInterface()) {

  ······

    try {
      knownMappers.put(type, new MapperProxyFactory<>(type));
      // It's important that the type is added before the parser is run
      // otherwise the binding may automatically be attempted by the
      // mapper parser. If the type is already known, it won't try.
      CustomMapperAnnotationBuilder parser = new CustomMapperAnnotationBuilder(config, type);
      parser.parse();
      loadCompleted = true;
    } finally {
      if (!loadCompleted) {
        knownMappers.remove(type);
      }
    }
  }
}

CustomConfiguration

 修改 mapperRegistry 属性使用 CustomMapperRegistry。

public class CustomConfiguration extends Configuration {

  ······

  protected final MapperRegistry mapperRegistry = new CustomMapperRegistry(this);

  ······

}

在Spring中使用

<!-- Mybatis SessionFactory-->
<bean id="sqlSessionFactory" class="com.my.ibatis.SqlSessionFactoryBean">
  <property name="dataSource" ref="dataSource" />
  <property name="configurationProperties" >
    <bean class="org.springframework.beans.factory.config.PropertiesFactoryBean">
      <property name="locations" value="classpath*:mybatis.properties"/>
    </bean>
  </property>
</bean>

@Configuration
public class MybatisConfig {
  @Bean
  public PropertiesFactoryBean createPropertiesFactoryBean() throws IOException {
    PropertiesFactoryBean bean = new PropertiesFactoryBean();
    bean.setLocation(new ClassPathResource("mybatis.properties"));
    return bean;
  }

  @Bean("sqlSessionFactory")
  public SqlSessionFactoryBean createSqlSessionFactory(DataSource dataSource, PropertiesFactoryBean bean) throws IOException {
    SqlSessionFactoryBean factoryBean = new SqlSessionFactoryBean();
    factoryBean.setDataSource(dataSource);
    factoryBean.setConfigurationProperties(bean.getObject());
    return factoryBean;
  }
}

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