MyBatis 添加元数据自定义元素标签的实现代码
作者：小王886
这篇文章主要介绍了MyBatis 添加元数据自定义元素标签的实现代码，本文通过实例代码给大家介绍的非常详细，对大家的学习或工作具有一定的参考借鉴价值,需要的朋友可以参考下
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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