MyBatis中SqlSessionFactory
SqlSessionFactory的作用
根据mapper配置文件解析出dao与具体jdbc操作、resultMap与实体类等的映射关系
1.SpringBoot整合MyBatis如何加载SqlSessionFactory
1.1 SpringBoot自动装配Spring.factories文件
Spring.factories文件中EnableAutoConfiguration对应的值MybatisAutoConfiguration
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.mybatis.spring.boot.autoconfigure.MybatisLanguageDriverAutoConfiguration,\
org.mybatis.spring.boot.autoconfigure.MybatisAutoConfiguration
1.2 读取yml配置文件中的mybatis配置
mybatis:
mapper-locations: classpath:com/sunpy/demo/mapper/*Mapper.xml
type-aliases-package: com.sunpy.demo.entity
MybatisAutoConfiguration中注入MybatisProperties配置类，实现：
@EnableConfigurationProperties这个注解的作用会将使用 @ConfigurationProperties的类进行了一次注入。
MybatisProperties类使用@ConfigurationProperties映射属性：
mybatis.mapper-locations 映射为 mapperLocations字段
mybatis.type-aliases-package 映射为 typeAliasesPackage字段
1.3 MybatisAutoConfiguration中SqlSessionFactory
实现的功能：
① 使用SqlSessionFactoryBean类，这个类实现了FactoryBean
② 设置datasource数据源。
③ 扫描映射的po类。
④ 扫描加载mapper中的xml文件。
@Bean
@ConditionalOnMissingBean
public SqlSessionFactory sqlSessionFactory(DataSource dataSource) throws Exception {
// 设置数据源DataSource
SqlSessionFactoryBean factory = new SqlSessionFactoryBean();
factory.setDataSource(dataSource);
factory.setVfs(SpringBootVFS.class);
// 设置总配置文件，mybatis-config.xml
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);
}
// 读取MybatisProperties中属性值，设置mybatis自动扫描到自定义的POJO
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);
}
// 读取MybatisProperties中属性值，设置mapper-locations，扫描mapper的xml文件
if (!ObjectUtils.isEmpty(this.properties.resolveMapperLocations())) {
factory.setMapperLocations(this.properties.resolveMapperLocations());
}
Set<String> factoryPropertyNames = Stream
.of(new BeanWrapperImpl(SqlSessionFactoryBean.class).getPropertyDescriptors()).map(PropertyDescriptor::getName)
.collect(Collectors.toSet());
Class<? extends LanguageDriver> defaultLanguageDriver = this.properties.getDefaultScriptingLanguageDriver();
if (factoryPropertyNames.contains("scriptingLanguageDrivers") && !ObjectUtils.isEmpty(this.languageDrivers)) {
// Need to mybatis-spring 2.0.2+
factory.setScriptingLanguageDrivers(this.languageDrivers);
if (defaultLanguageDriver == null && this.languageDrivers.length == 1) {
defaultLanguageDriver = this.languageDrivers[0].getClass();
}
}
if (factoryPropertyNames.contains("defaultScriptingLanguageDriver")) {
// Need to mybatis-spring 2.0.2+
factory.setDefaultScriptingLanguageDriver(defaultLanguageDriver);
}
// 创建SqlSessionFactory对象
return factory.getObject();
}
1.4 注册SqlSessionFactory类到spring的逻辑
自动装配的逻辑中使用ConfigurationClassPostProcessor这个处理@Configuration注解的后置处理器，使用registerBeanDefinition方法，将当前的SqlSessionFactory类放入beanDefinitionMap中。
2. 细看SqlSessionFactoryBean实例化SqlSessionFactory
2.1 调用getObject方法实例化SqlSessionFactory
@Override
public SqlSessionFactory getObject() throws Exception {
if (this.sqlSessionFactory == null) {
afterPropertiesSet();
}
return this.sqlSessionFactory;
}
@Override
public void afterPropertiesSet() throws Exception {
notNull(dataSource, "Property 'dataSource' is required");
notNull(sqlSessionFactoryBuilder, "Property 'sqlSessionFactoryBuilder' is required");
state((configuration == null && configLocation == null) || !(configuration != null && configLocation != null),
"Property 'configuration' and 'configLocation' can not specified with together");
this.sqlSessionFactory = buildSqlSessionFactory();
}
2.2 核心实现，委派给buildSqlSessionFactory()方法，构建SqlSessionFactory对象
- 解析this.typeAliasesPackage，扫描到自定义的POJO，存放到this.typeAliases
- 遍历mapper-locations，扫描mapper的所有xml文件，解析xml文件
protected SqlSessionFactory buildSqlSessionFactory() throws Exception {
final Configuration targetConfiguration;
XMLConfigBuilder 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) {
xmlConfigBuilder = new XMLConfigBuilder(this.configLocation.getInputStream(), null, this.configurationProperties);
targetConfiguration = xmlConfigBuilder.getConfiguration();
} else {
LOGGER.debug(
() -> "Property 'configuration' or 'configLocation' not specified, using default MyBatis Configuration");
targetConfiguration = new Configuration();
Optional.ofNullable(this.configurationProperties).ifPresent(targetConfiguration::setVariables);
}
Optional.ofNullable(this.objectFactory).ifPresent(targetConfiguration::setObjectFactory);
Optional.ofNullable(this.objectWrapperFactory).ifPresent(targetConfiguration::setObjectWrapperFactory);
Optional.ofNullable(this.vfs).ifPresent(targetConfiguration::setVfsImpl);
// 扫描到自定义的POJO，存放到this.typeAliases
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);
}
if (!isEmpty(this.typeAliases)) {
Stream.of(this.typeAliases).forEach(typeAlias -> {
targetConfiguration.getTypeAliasRegistry().registerAlias(typeAlias);
LOGGER.debug(() -> "Registered type alias: '" + typeAlias + "'");
});
}
if (!isEmpty(this.plugins)) {
Stream.of(this.plugins).forEach(plugin -> {
targetConfiguration.addInterceptor(plugin);
LOGGER.debug(() -> "Registered plugin: '" + plugin + "'");
});
}
if (hasLength(this.typeHandlersPackage)) {
scanClasses(this.typeHandlersPackage, TypeHandler.class).stream().filter(clazz -> !clazz.isAnonymousClass())
.filter(clazz -> !clazz.isInterface()).filter(clazz -> !Modifier.isAbstract(clazz.getModifiers()))
.forEach(targetConfiguration.getTypeHandlerRegistry()::register);
}
if (!isEmpty(this.typeHandlers)) {
Stream.of(this.typeHandlers).forEach(typeHandler -> {
targetConfiguration.getTypeHandlerRegistry().register(typeHandler);
LOGGER.debug(() -> "Registered type handler: '" + typeHandler + "'");
});
}
targetConfiguration.setDefaultEnumTypeHandler(defaultEnumTypeHandler);
if (!isEmpty(this.scriptingLanguageDrivers)) {
Stream.of(this.scriptingLanguageDrivers).forEach(languageDriver -> {
targetConfiguration.getLanguageRegistry().register(languageDriver);
LOGGER.debug(() -> "Registered scripting language driver: '" + languageDriver + "'");
});
}
Optional.ofNullable(this.defaultScriptingLanguageDriver)
.ifPresent(targetConfiguration::setDefaultScriptingLanguage);
if (this.databaseIdProvider != null) {// fix #64 set databaseId before parse mapper xmls
try {
targetConfiguration.setDatabaseId(this.databaseIdProvider.getDatabaseId(this.dataSource));
} catch (SQLException e) {
throw new NestedIOException("Failed getting a databaseId", e);
}
}
Optional.ofNullable(this.cache).ifPresent(targetConfiguration::addCache);
if (xmlConfigBuilder != null) {
try {
xmlConfigBuilder.parse();
LOGGER.debug(() -> "Parsed configuration file: '" + this.configLocation + "'");
} catch (Exception ex) {
throw new NestedIOException("Failed to parse config resource: " + this.configLocation, ex);
} finally {
ErrorContext.instance().reset();
}
}
targetConfiguration.setEnvironment(new Environment(this.environment,
this.transactionFactory == null ? new SpringManagedTransactionFactory() : this.transactionFactory,
this.dataSource));
// 遍历mapper-locations，扫描mapper的所有xml文件
if (this.mapperLocations != null) {
if (this.mapperLocations.length == 0) {
LOGGER.warn(() -> "Property 'mapperLocations' was specified but matching resources are not found.");
} else {
for (Resource mapperLocation : this.mapperLocations) {
if (mapperLocation == null) {
continue;
}
try {
XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(mapperLocation.getInputStream(),
targetConfiguration, mapperLocation.toString(), targetConfiguration.getSqlFragments());
// 解析mapper的xml文件
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.");
}
return this.sqlSessionFactoryBuilder.build(targetConfiguration);
}
3. 细看this.typeAliasesPackage指定的扫描po类加载存放到this.typeAliases
scanClasses(this.typeAliasesPackage, this.typeAliasesSuperType).stream()
.filter(clazz -> !clazz.isAnonymousClass()).filter(clazz -> !clazz.isInterface())
.filter(clazz -> !clazz.isMemberClass()).forEach(targetConfiguration.getTypeAliasRegistry()::registerAlias);
scanClasses实现
// 扫描指定packagePatterns路径下的类
private Set<Class<?>> scanClasses(String packagePatterns, Class<?> assignableType) throws IOException {
Set<Class<?>> classes = new HashSet<>();
// 根据指定的标记将字符串转换为字符串数组
String[] packagePatternArray = tokenizeToStringArray(packagePatterns,
ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
for (String packagePattern : packagePatternArray) {
// 加载拼接的指定路径下的所有类
Resource[] resources = RESOURCE_PATTERN_RESOLVER.getResources(ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX
+ ClassUtils.convertClassNameToResourcePath(packagePattern) + "/**/*.class");
for (Resource resource : resources) {
try {
ClassMetadata classMetadata = METADATA_READER_FACTORY.getMetadataReader(resource).getClassMetadata();
Class<?> clazz = Resources.classForName(classMetadata.getClassName());
// 搜集加载的类
if (assignableType == null || assignableType.isAssignableFrom(clazz)) {
classes.add(clazz);
}
} catch (Throwable e) {
LOGGER.warn(() -> "Cannot load the '" + resource + "'. Cause by " + e.toString());
}
}
}
return classes;
}
4. 细看遍历mapper-locations，扫描mapper的所有xml文件，解析xml文件
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 + "'");
}
技术收获
1. 根据指定的标记将字符串转换为字符串数组
String[] packagePatternArray = tokenizeToStringArray(packagePatterns,
ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
2. 加载指定路径下的所有类
Resource[] resources = RESOURCE_PATTERN_RESOLVER.getResources(ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX
+ ClassUtils.convertClassNameToResourcePath(packagePattern) + "//*.class");**
3. 解析加载xml文件
xmlMapperBuilder.parse();
