Mybatis sql与xml文件读取方法详细分析
xl649138628 人气:0在执行一个自定义sql语句时，dao对应的代理对象时如何找到sql，也就是dao的代理对象和sql之间的关联关系是如何建立的。
在mybatis中的MybatisPlusAutoConfiguration类被@Configuration注解，在该类中通过被@Bean注解的sqlSessionFactory方法向spring上下文注入bean并生成SqlSessionFactory类型的bean实例。关注该方法的最后一行代码。
@Bean
@ConditionalOnMissingBean
public SqlSessionFactory sqlSessionFactory(DataSource dataSource) throws Exception {
// TODO 使用 MybatisSqlSessionFactoryBean 而不是 SqlSessionFactoryBean
MybatisSqlSessionFactoryBean factory = new MybatisSqlSessionFactoryBean();
factory.setDataSource(dataSource);
factory.setVfs(SpringBootVFS.class);
if (StringUtils.hasText(this.properties.getConfigLocation())) {
factory.setConfigLocation(this.resourceLoader.getResource(this.properties.getConfigLocation()));
}
applyConfiguration(factory);
if (this.properties.getConfigurationProperties() != null) {
factory.setConfigurationProperties(this.properties.getConfigurationProperties());
}
if (!ObjectUtils.isEmpty(this.interceptors)) {
factory.setPlugins(this.interceptors);
}
if (this.databaseIdProvider != null) {
factory.setDatabaseIdProvider(this.databaseIdProvider);
}
if (StringUtils.hasLength(this.properties.getTypeAliasesPackage())) {
factory.setTypeAliasesPackage(this.properties.getTypeAliasesPackage());
}
if (this.properties.getTypeAliasesSuperType() != null) {
factory.setTypeAliasesSuperType(this.properties.getTypeAliasesSuperType());
}
if (StringUtils.hasLength(this.properties.getTypeHandlersPackage())) {
factory.setTypeHandlersPackage(this.properties.getTypeHandlersPackage());
}
if (!ObjectUtils.isEmpty(this.typeHandlers)) {
factory.setTypeHandlers(this.typeHandlers);
}
Resource[] mapperLocations = this.properties.resolveMapperLocations();
if (!ObjectUtils.isEmpty(mapperLocations)) {
factory.setMapperLocations(mapperLocations);
}
// TODO 修改源码支持定义 TransactionFactory
this.getBeanThen(TransactionFactory.class, factory::setTransactionFactory);
// TODO 对源码做了一定的修改(因为源码适配了老旧的mybatis版本,但我们不需要适配)
Class<? extends LanguageDriver> defaultLanguageDriver = this.properties.getDefaultScriptingLanguageDriver();
if (!ObjectUtils.isEmpty(this.languageDrivers)) {
factory.setScriptingLanguageDrivers(this.languageDrivers);
}
Optional.ofNullable(defaultLanguageDriver).ifPresent(factory::setDefaultScriptingLanguageDriver);
// TODO 自定义枚举包
if (StringUtils.hasLength(this.properties.getTypeEnumsPackage())) {
factory.setTypeEnumsPackage(this.properties.getTypeEnumsPackage());
}
// TODO 此处必为非 NULL
GlobalConfig globalConfig = this.properties.getGlobalConfig();
// TODO 注入填充器
this.getBeanThen(MetaObjectHandler.class, globalConfig::setMetaObjectHandler);
// TODO 注入主键生成器
this.getBeanThen(IKeyGenerator.class, i -> globalConfig.getDbConfig().setKeyGenerator(i));
// TODO 注入sql注入器
this.getBeanThen(ISqlInjector.class, globalConfig::setSqlInjector);
// TODO 注入ID生成器
this.getBeanThen(IdentifierGenerator.class, globalConfig::setIdentifierGenerator);
// TODO 设置 GlobalConfig 到 MybatisSqlSessionFactoryBean
factory.setGlobalConfig(globalConfig);
//关注该行代码
return factory.getObject();
}进入最后一行代码找到MybatisSqlSessionFactoryBean类里的getObject方法，然后进入到该类的afterPropertiesSet方法，找到了buildSqlSessionFactory方法。
public SqlSessionFactory getObject() throws Exception {
if (this.sqlSessionFactory == null) {
//关注该行方法
afterPropertiesSet();
}
return this.sqlSessionFactory;
}public void afterPropertiesSet() throws Exception {
notNull(dataSource, "Property 'dataSource' is required");
state((configuration == null && configLocation == null) || !(configuration != null && configLocation != null),
"Property 'configuration' and 'configLocation' can not specified with together");
//关注该行方法
this.sqlSessionFactory = buildSqlSessionFactory();
}在buildSqlSessionFactory中有两处代码比较关键，第一处如下图hasLength(this.typeAliasesPackage)判断了在yml中配置的的mybatis-plus.typeAliasesPackage,并通过buildSqlSessionFactory方法里的scanClasses方法将读取到的类路径全部小写后存放到TypeAliasRegistry类的typeAliases属性的hashMap缓存中。
mybatis-plus:
mapper-locations: classpath*:mapper/*.xml
typeAliasesPackage: >
com.changshin.entity.po
global-config:
id-type: 0 # 0:数据库ID自增 1:用户输入id 2:全局唯一id(IdWorker) 3:全局唯一ID(uuid)
db-column-underline: false
refresh-mapper: true
configuration:
map-underscore-to-camel-case: true
cache-enabled: true #配置的缓存的全局开关
lazyLoadingEnabled: true #延时加载的开关
multipleResultSetsEnabled: true #开启的话，延时加载一个属性时会加载该对象全部属性，否则按需加载属性 protected SqlSessionFactory buildSqlSessionFactory() throws Exception {
final Configuration targetConfiguration;
// TODO 使用 MybatisXmlConfigBuilder 而不是 XMLConfigBuilder
MybatisXMLConfigBuilder 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) {
// TODO 使用 MybatisXMLConfigBuilder
xmlConfigBuilder = new MybatisXMLConfigBuilder(this.configLocation.getInputStream(), null, this.configurationProperties);
targetConfiguration = xmlConfigBuilder.getConfiguration();
} else {
LOGGER.debug(() -> "Property 'configuration' or 'configLocation' not specified, using default MyBatis Configuration");
// TODO 使用 MybatisConfiguration
targetConfiguration = new MybatisConfiguration();
Optional.ofNullable(this.configurationProperties).ifPresent(targetConfiguration::setVariables);
}
//省略。。。。。。。
if (hasLength(this.typeAliasesPackage)) {
scanClasses(this.typeAliasesPackage, this.typeAliasesSuperType).stream()
.filter(clazz -> !clazz.isAnonymousClass()).filter(clazz -> !clazz.isInterface())
.filter(clazz -> !clazz.isMemberClass()).forEach(targetConfiguration.getTypeAliasRegistry()::registerAlias);
}
//省略。。。。。。。。。。。。。。。。。。。。。。。。
if (this.mapperLocations != null) {
if (this.mapperLocations.length == 0) {
LOGGER.warn(() -> "Property 'mapperLocations' was specified but matching resources are not found.");
} else {
// 关注for循环结构体里的代码
for (Resource mapperLocation : this.mapperLocations) {
if (mapperLocation == null) {
continue;
}
try {
XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(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();
}
LOGGER.debug(() -> "Parsed mapper file: '" + mapperLocation + "'");
}
}
} else {
LOGGER.debug(() -> "Property 'mapperLocations' was not specified.");
}
final SqlSessionFactory sqlSessionFactory = new MybatisSqlSessionFactoryBuilder().build(targetConfiguration);
// TODO SqlRunner
SqlHelper.FACTORY = sqlSessionFactory;
// TODO 打印骚东西 Banner
if (globalConfig.isBanner()) {
System.out.println(" _ _ |_ _ _|_. ___ _ | _ ");
System.out.println("| | |\\/|_)(_| | |_\\ |_)||_|_\\ ");
System.out.println(" / | ");
System.out.println(" " + MybatisPlusVersion.getVersion() + " ");
}
return sqlSessionFactory;
}第二处xmlMapperBuilder.parse()方法解析了xml文件，mapperLocations属性是一个数组类型的属性，数组里存储了xml文件的全路径。通
过for循环对每一个xml进行解析。进入parse方法。在进入parse方法前初始化了XMLMapperBuilder并将其configuration属性设置为MybatisSqlSessionFactoryBean的configuration属性属性。
XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(mapperLocation.getInputStream(),
targetConfiguration, mapperLocation.toString(), targetConfiguration.getSqlFragments());对parse方法进行解析
public void parse() {
//判断是否加载过配置文件
if (!configuration.isResourceLoaded(resource)) {
//解析mapper标签
configurationElement(parser.evalNode("/mapper"));
//标注该配置已经被加载过了
configuration.addLoadedResource(resource);
//将dao对应的类与xml mapper标签的namespaces属性做绑定
bindMapperForNamespace();
}
parsePendingResultMaps();
parsePendingCacheRefs();
parsePendingStatements();
}先分析 parse方法里的configurationElement方法。该方法逐步解析mapper标签下的子标签,具体解析过程比较复杂在此就不分析了。
private void configurationElement(XNode context) {
try {
String namespace = context.getStringAttribute("namespace");
if (namespace == null || namespace.isEmpty()) {
throw new BuilderException("Mapper's namespace cannot be empty");
}
builderAssistant.setCurrentNamespace(namespace);
cacheRefElement(context.evalNode("cache-ref"));
cacheElement(context.evalNode("cache"));
parameterMapElement(context.evalNodes("/mapper/parameterMap"));
resultMapElements(context.evalNodes("/mapper/resultMap"));
sqlElement(context.evalNodes("/mapper/sql"));
buildStatementFromContext(context.evalNodes("select|insert|update|delete"));
} catch (Exception e) {
throw new BuilderException("Error parsing Mapper XML. The XML location is '" + resource + "'. Cause: " + e, e);
}
}bindMapperForNamespace方法将namespace将生成的的类类型通过
configuration.addMapper(boundType)方法放到Configuration类的MapperRegistry类型属性mapperRegistry的knownMappers属性的缓存中（该属性是一个以类类型key，MapperProxyFactory为value的HashMap）。
private void bindMapperForNamespace() {
String namespace = builderAssistant.getCurrentNamespace();
if (namespace != null) {
Class<?> boundType = null;
try {
boundType = Resources.classForName(namespace);
} catch (ClassNotFoundException e) {
// ignore, bound type is not required
}
if (boundType != null && !configuration.hasMapper(boundType)) {
// Spring may not know the real resource name so we set a flag
// to prevent loading again this resource from the mapper interface
// look at MapperAnnotationBuilder#loadXmlResource
configuration.addLoadedResource("namespace:" + namespace);
configuration.addMapper(boundType);
}
}
}加载全部内容