Mybatis源码解析之Spring集成mybatis-spring分析
Mybatis源码解析之核心类分析
Mybatis源码解析之初始化分析
Mybatis源码解析之执行流程解析
Mybatis源码解析之数据库连接和连接池
Mybatis源码解析之事务管理
Mybatis源码解析之缓存机制（一）：一级缓存
Mybatis源码解析之缓存机制（二）：二级缓存
Mybatis源码解析之插件机制
Mybatis源码解析之mapper接口的代理模式
Mybatis源码解析之DefaultResultSetHandler的handleResultSets方法解析
前面的几篇相关博客都针对原生的mybatis进行解析，从本文开始将针对mybatis和spring的集成进行解析。若无特殊说明，所有的源码都基于org.mybatis:mybatis-spring:1.3.1的jar包
一、jar包介绍
mybatis-spring是spring与mybatis的集成jar包，因此对spring和mybatis的相关jar包都存在依赖。
二、配置文件
在spring中集成mybatis框架，主要需要对以下两者进行bean注入。
1. SqlSessionFactory
SqlSessionFactory通过SqlSessionFactoryBeanFactory注入，其中的configLocation指定mybatis的配置文件，datasource指定数据源，我们还可以通过property注入其他的一些属性，不在意义列举，通过后续的源码解析会有一定了解。
2. mapper
除了SqlSessionFactory外，我们还有必要将mapper接口进行注入，可以通过注解、配置文件等多种方式注入，此处分别以MapperFactoryBean和MapperScannerConfigurer两种方式为例。
//MapperFactoryBean单个注入
//MapperScannerConfigurer路径扫描批量注入
三、SqlSessionFactoryBean
SqlSessionFactoryBean实现类FactoryBean和InitializingBean接口，基于spring的了解我们明白其注入的是getObject()方法的返回值，跟踪方法的调用，我们可以发现核心逻辑在SqlSessionFactoryBean#buildSqlSessionFactory()方法中。
1. SqlSessionFactoryBean#buildSqlSessionFactory()
protected SqlSessionFactory buildSqlSessionFactory() throws IOException {
Configuration configuration;
//configuration的几种配置方式
XMLConfigBuilder xmlConfigBuilder = null;
if (this.configuration != null) {
configuration = this.configuration;
if (configuration.getVariables() == null) {
configuration.setVariables(this.configurationProperties);
} else if (this.configurationProperties != null) {
configuration.getVariables().putAll(this.configurationProperties);
}
} else if (this.configLocation != null) {
xmlConfigBuilder = new XMLConfigBuilder(this.configLocation.getInputStream(), null, this.configurationProperties);
configuration = xmlConfigBuilder.getConfiguration();
} else {
if (LOGGER.isDebugEnabled()) {
LOGGER.debug("Property 'configuration' or 'configLocation' not specified, using default MyBatis Configuration");
}
configuration = new Configuration();
if (this.configurationProperties != null) {
configuration.setVariables(this.configurationProperties);
}
}
//objectFactory配置
if (this.objectFactory != null) {
configuration.setObjectFactory(this.objectFactory);
}
//objectWrapperFactory 配置
if (this.objectWrapperFactory != null) {
configuration.setObjectWrapperFactory(this.objectWrapperFactory);
}
//vfs配置
if (this.vfs != null) {
configuration.setVfsImpl(this.vfs);
}
//typeAliasesPackage配置，注册aliase
if (hasLength(this.typeAliasesPackage)) {
String[] typeAliasPackageArray = tokenizeToStringArray(this.typeAliasesPackage,
ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
for (String packageToScan : typeAliasPackageArray) {
configuration.getTypeAliasRegistry().registerAliases(packageToScan,
typeAliasesSuperType == null ? Object.class : typeAliasesSuperType);
if (LOGGER.isDebugEnabled()) {
LOGGER.debug("Scanned package: '" + packageToScan + "' for aliases");
}
}
}
//typeAliases配置，注册aliase
if (!isEmpty(this.typeAliases)) {
for (Class typeAlias : this.typeAliases) {
configuration.getTypeAliasRegistry().registerAlias(typeAlias);
if (LOGGER.isDebugEnabled()) {
LOGGER.debug("Registered type alias: '" + typeAlias + "'");
}
}
}
//插件plugin配置
if (!isEmpty(this.plugins)) {
for (Interceptor plugin : this.plugins) {
configuration.addInterceptor(plugin);
if (LOGGER.isDebugEnabled()) {
LOGGER.debug("Registered plugin: '" + plugin + "'");
}
}
}
//typeHandlersPackage配置，注册typeHandlers
if (hasLength(this.typeHandlersPackage)) {
String[] typeHandlersPackageArray = tokenizeToStringArray(this.typeHandlersPackage,
ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
for (String packageToScan : typeHandlersPackageArray) {
configuration.getTypeHandlerRegistry().register(packageToScan);
if (LOGGER.isDebugEnabled()) {
LOGGER.debug("Scanned package: '" + packageToScan + "' for type handlers");
}
}
}
//typeHandlersP配置，注册typeHandlers
if (!isEmpty(this.typeHandlers)) {
for (TypeHandler typeHandler : this.typeHandlers) {
configuration.getTypeHandlerRegistry().register(typeHandler);
if (LOGGER.isDebugEnabled()) {
LOGGER.debug("Registered type handler: '" + typeHandler + "'");
}
}
}
//databaseIdProvider
if (this.databaseIdProvider != null) {//fix #64 set databaseId before parse mapper xmls
try {
configuration.setDatabaseId(this.databaseIdProvider.getDatabaseId(this.dataSource));
} catch (SQLException e) {
throw new NestedIOException("Failed getting a databaseId", e);
}
}
if (this.cache != null) {
configuration.addCache(this.cache);
}
if (xmlConfigBuilder != null) {
try {
xmlConfigBuilder.parse();
if (LOGGER.isDebugEnabled()) {
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();
}
}
//transactionFactory
if (this.transactionFactory == null) {
//事务默认采用SpringManagedTransaction
this.transactionFactory = new SpringManagedTransactionFactory();
}
//environment
configuration.setEnvironment(new Environment(this.environment, this.transactionFactory, this.dataSource));
//mapperLocations
if (!isEmpty(this.mapperLocations)) {
for (Resource mapperLocation : this.mapperLocations) {
if (mapperLocation == null) {
continue;
}
try {
XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(mapperLocation.getInputStream(),
configuration, mapperLocation.toString(), configuration.getSqlFragments());
xmlMapperBuilder.parse();
} catch (Exception e) {
throw new NestedIOException("Failed to parse mapping resource: '" + mapperLocation + "'", e);
} finally {
ErrorContext.instance().reset();
}
if (LOGGER.isDebugEnabled()) {
LOGGER.debug("Parsed mapper file: '" + mapperLocation + "'");
}
}
} else {
if (LOGGER.isDebugEnabled()) {
LOGGER.debug("Property 'mapperLocations' was not specified or no matching resources found");
}
}
return this.sqlSessionFactoryBuilder.build(configuration);
}
可以看到，其作用就是根据配置文件中的property属性生成mybatis的configuration对象，并组装到sqlSessionFactory中，这一点相当于前面介绍的原生的mybatis的初始化过程。
其中，datasource属性和configLocation(configuration、configurationProperties)和mapperLocations是其中比较基础也比较重要的属性配置，另外，当配置中未指定事务时，mybatis-spring默认采用SpringManagedTransaction。
四、SpringManagedTransaction
1. 类图
可以看到，相比于原生mybatis，mybatis-spring提供了SpringManagedTransaction并作为默认的事务机制。
顾名思义，SpringManagedTransaction将mybatis的事务管理委托给spring事务进行处理。
2. SpringManagedTransaction#openConnection()
private void openConnection() throws SQLException {
this.connection = DataSourceUtils.getConnection(this.dataSource);
this.autoCommit = this.connection.getAutoCommit();
this.isConnectionTransactional = DataSourceUtils.isConnectionTransactional(this.connection, this.dataSource);
if (LOGGER.isDebugEnabled()) {
LOGGER.debug(
"JDBC Connection ["
+ this.connection
+ "] will"
+ (this.isConnectionTransactional ? " " : " not ")
+ "be managed by Spring");
}
获取connection的逻辑交给了spring-jdbc的工具类DataSourceUtils。
3. DataSourceUtils#doGetConnection(DataSource)
public static Connection doGetConnection(DataSource dataSource) throws SQLException {
Assert.notNull(dataSource, "No DataSource specified");
//从县城获取ConnectionHolder
ConnectionHolder conHolder = (ConnectionHolder) TransactionSynchronizationManager.getResource(dataSource);
if (conHolder != null && (conHolder.hasConnection() || conHolder.isSynchronizedWithTransaction())) {
//请求，计数加1
conHolder.requested();
if (!conHolder.hasConnection()) {
logger.debug("Fetching resumed JDBC Connection from DataSource");
//从数据库获取连接
conHolder.setConnection(dataSource.getConnection());
}
return conHolder.getConnection();
}
// Else we either got no holder or an empty thread-bound holder here.
logger.debug("Fetching JDBC Connection from DataSource");
Connection con = dataSource.getConnection();
//事务同步是否处于active状态
if (TransactionSynchronizationManager.isSynchronizationActive()) {
logger.debug("Registering transaction synchronization for JDBC Connection");
// Use same Connection for further JDBC actions within the transaction.
// Thread-bound object will get removed by synchronization at transaction completion.
ConnectionHolder holderToUse = conHolder;
if (holderToUse == null) {
holderToUse = new ConnectionHolder(con);
}
else {
holderToUse.setConnection(con);
}
holderToUse.requested();
当前线程注册新的同步事务
TransactionSynchronizationManager.registerSynchronization(
new ConnectionSynchronization(holderToUse, dataSource));
holderToUse.setSynchronizedWithTransaction(true);
if (holderToUse != conHolder) {
//绑定
TransactionSynchronizationManager.bindResource(dataSource, holderToUse);
}
}
return con;
}
DataSourceUtils#getConnection(DataSource)又将具体逻辑交给了doGetConnection(DataSource)方法。
spring会将事务和线程绑定，因此直接从线程中获取连接，不存在再从数据源申请连接，并绑定到线程中。
并且，ConnectionHolder维护着一个引用计数器，每次获取连接时，会增加一次计数，释放连接（doReleaseConnection）时再将计数减少。
五、MapperFactoryBean
MapperFacotryBean同样实现了FactoryBean和initializingBean接口，注入IOC容器的同样是getObject()方法的返回值。
1. DaoSupport#afterPropertiesSet()
@Override
public final void afterPropertiesSet() throws IllegalArgumentException, BeanInitializationException {
// Let abstract subclasses check their configuration.
checkDaoConfig();
// Let concrete implementations initialize themselves.
try {
initDao();
}
catch (Exception ex) {
throw new BeanInitializationException("Initialization of DAO failed", ex);
}
}
MapperFactoryBean并没有重写afterPropertiesSet方法，其使用的是父类DaoSupport的方法，先checkDaoConfig()方法检查再initDao()进行初始化。
2. MapperFactoryBean#checkDaoConfig()
protected void checkDaoConfig() {
super.checkDaoConfig();
notNull(this.mapperInterface, "Property 'mapperInterface' is required");
Configuration configuration = getSqlSession().getConfiguration();
if (this.addToConfig && !configuration.hasMapper(this.mapperInterface)) {
try {
configuration.addMapper(this.mapperInterface);
} catch (Exception e) {
logger.error("Error while adding the mapper '" + this.mapperInterface + "' to configuration.", e);
throw new IllegalArgumentException(e);
} finally {
ErrorContext.instance().reset();
}
}
}
addToConfig为true时（默认为true），如果mapper接口没有被配置加入configuration中，手动加入。
3. DaoSupport#initDao()
protected void initDao() throws Exception {
}
MapperFactory同样没有重写initDao()方法，而在DaoSupport中也只是个空方法。
4. MapperFactoryBean#getObject()
@Override
public T getObject() throws Exception {
return getSqlSession().getMapper(this.mapperInterface);
}
可以看到，返回的是mapper接口的代理类对象。
六、MapperScannerConfiguer
1. 类图
2.MapperScannerConfiguer#postProcessBeanDefinitionRegistry(BeanDefinitionRegistry)
@Override
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {
if (this.processPropertyPlaceHolders) {
processPropertyPlaceHolders();
}
ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry);
scanner.setAddToConfig(this.addToConfig);
scanner.setAnnotationClass(this.annotationClass);
scanner.setMarkerInterface(this.markerInterface);
scanner.setSqlSessionFactory(this.sqlSessionFactory);
scanner.setSqlSessionTemplate(this.sqlSessionTemplate);
scanner.setSqlSessionFactoryBeanName(this.sqlSessionFactoryBeanName);
scanner.setSqlSessionTemplateBeanName(this.sqlSessionTemplateBeanName);
scanner.setResourceLoader(this.applicationContext);
scanner.setBeanNameGenerator(this.nameGenerator);
scanner.registerFilters();
scanner.scan(StringUtils.tokenizeToStringArray(this.basePackage, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS));
}
可以看到在方法中构建了ClassPathMapperScanner对象进行扫描。
此处还会通过processPropertyPlaceHolders()方法手动引入properties属性。
BeanDefinitionRegistries会在应用启动的时候调用，并且会早于BeanFactoryPostProcessors的调用，这就意味着PropertyResourceConfigurers还没有被加载所以任何对于属性文件的引用将会失效，为了避免这种情况的发生，此方法手动找出定义的PropertyResourceConfigurers并进行提前调用以保证对于属性的引用可以正常工作”。
3. ClassPathMapperScanner#registerFilters()
public void registerFilters() {
boolean acceptAllInterfaces = true;
// if specified, use the given annotation and / or marker interface
if (this.annotationClass != null) {
addIncludeFilter(new AnnotationTypeFilter(this.annotationClass));
acceptAllInterfaces = false;
}
// override AssignableTypeFilter to ignore matches on the actual marker interface
if (this.markerInterface != null) {
addIncludeFilter(new AssignableTypeFilter(this.markerInterface) {
@Override
protected boolean matchClassName(String className) {
return false;
}
});
acceptAllInterfaces = false;
}
if (acceptAllInterfaces) {
// default include filter that accepts all classes
addIncludeFilter(new TypeFilter() {
@Override
public boolean match(MetadataReader metadataReader, MetadataReaderFactory metadataReaderFactory) throws IOException {
return true;
}
});
}
// exclude package-info.java
addExcludeFilter(new TypeFilter() {
@Override
public boolean match(MetadataReader metadataReader, MetadataReaderFactory metadataReaderFactory) throws IOException {
String className = metadataReader.getClassMetadata().getClassName();
return className.endsWith("package-info");
}
});
}
可以看到，ClassPathMapperScanner根据annotationClass和markerInterface判断是是否匹配，并需要排除package-info.java。
4. ClassPathMapperScanner#doScan(String …)
@Override
public Set doScan(String... basePackages) {
Set beanDefinitions = super.doScan(basePackages);
if (beanDefinitions.isEmpty()) {
logger.warn("No MyBatis mapper was found in '" + Arrays.toString(basePackages) + "' package. Please check your configuration.");
} else {
processBeanDefinitions(beanDefinitions);
}
return beanDefinitions;
}
ClassPathMapperScanner是ClassPathBeanDefinitionScanner的子类，扫描的核心逻辑委托给了doScan方法。
方法中，根据父类的doScan找出匹配的类，然后交给processBeanDefinitions注入IOC容器。
5. ClassPathBeanDefinitionScanner#doScan(String …)
protected Set doScan(String... basePackages) {
Assert.notEmpty(basePackages, "At least one base package must be specified");
Set beanDefinitions = new LinkedHashSet();
//遍历basePackages进行扫描
for (String basePackage : basePackages) {
//找出匹配的类
Set candidates = findCandidateComponents(basePackage);
for (BeanDefinition candidate : candidates) {
ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate);
candidate.setScope(scopeMetadata.getScopeName());
String beanName = this.beanNameGenerator.generateBeanName(candidate, this.registry);
if (candidate instanceof AbstractBeanDefinition) {
postProcessBeanDefinition((AbstractBeanDefinition) candidate, beanName);
}
if (candidate instanceof AnnotatedBeanDefinition) {
AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition) candidate);
}
if (checkCandidate(beanName, candidate)) {
//封装成BeanDefinitionHolder 对象
BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName);
definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
beanDefinitions.add(definitionHolder);
registerBeanDefinition(definitionHolder, this.registry);
}
}
}
return beanDefinitions;
}
该方法时spring通用的扫描bean的方法，不展开分析。
6. ClassPathMapperScanner#processBeanDefinition(Set)
private void processBeanDefinitions(Set beanDefinitions) {
GenericBeanDefinition definition;
for (BeanDefinitionHolder holder : beanDefinitions) {
definition = (GenericBeanDefinition) holder.getBeanDefinition();
if (logger.isDebugEnabled()) {
logger.debug("Creating MapperFactoryBean with name '" + holder.getBeanName()
+ "' and '" + definition.getBeanClassName() + "' mapperInterface");
}
// the mapper interface is the original class of the bean
// but, the actual class of the bean is MapperFactoryBean
definition.getConstructorArgumentValues().addGenericArgumentValue(definition.getBeanClassName()); // issue #59
definition.setBeanClass(this.mapperFactoryBean.getClass());
definition.getPropertyValues().add("addToConfig", this.addToConfig);
boolean explicitFactoryUsed = false;
if (StringUtils.hasText(this.sqlSessionFactoryBeanName)) {
definition.getPropertyValues().add("sqlSessionFactory", new RuntimeBeanReference(this.sqlSessionFactoryBeanName));
explicitFactoryUsed = true;
} else if (this.sqlSessionFactory != null) {
definition.getPropertyValues().add("sqlSessionFactory", this.sqlSessionFactory);
explicitFactoryUsed = true;
}
if (StringUtils.hasText(this.sqlSessionTemplateBeanName)) {
if (explicitFactoryUsed) {
logger.warn("Cannot use both: sqlSessionTemplate and sqlSessionFactory together. sqlSessionFactory is ignored.");
}
definition.getPropertyValues().add("sqlSessionTemplate", new RuntimeBeanReference(this.sqlSessionTemplateBeanName));
explicitFactoryUsed = true;
} else if (this.sqlSessionTemplate != null) {
if (explicitFactoryUsed) {
logger.warn("Cannot use both: sqlSessionTemplate and sqlSessionFactory together. sqlSessionFactory is ignored.");
}
definition.getPropertyValues().add("sqlSessionTemplate", this.sqlSessionTemplate);
explicitFactoryUsed = true;
}
if (!explicitFactoryUsed) {
if (logger.isDebugEnabled()) {
logger.debug("Enabling autowire by type for MapperFactoryBean with name '" + holder.getBeanName() + "'.");
}
definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE);
}
}
}
可以看到，方法中根据MapperScannerConfigurer的属性将扫描结果封装成GenericBeanDefinition。
重点下面两行代码
// the mapper interface is the original class of the bean
// but, the actual class of the bean is MapperFactoryBean
definition.getConstructorArgumentValues().addGenericArgumentValue(definition.getBeanClassName()); // issue #59
definition.setBeanClass(this.mapperFactoryBean.getClass());
可以看到注入的bean的类型是MapperFactoryBean，扫描出来的类只作为MapperFactoryBean的构造器参数，这一点和MapperFactoryBean的构造器方法相吻合。
public MapperFactoryBean(Class mapperInterface) {
this.mapperInterface = mapperInterface;
}
最终又回到了我们前面分析的MapperFactoryBean的注入。