要想使用spring的事务,要加入mybatis-spring依赖包
<!-- 引用插件依赖：MyBatis整合Spring --><dependency><groupId>org.mybatis</groupId><artifactId>mybatis-spring</artifactId><version>1.3.0</version></dependency>配置文件:
<?xml version="1.0" encoding="UTF-8"?><context:property-placeholderlocation="classpath:properties/*.properties" /><beanid="dataSource"class="com.alibaba.druid.pool.DruidDataSource"destroy-method="close"><propertyname="url"value="${jdbc.url}" /><propertyname="username"value="${jdbc.username}" /><propertyname="password"value="${jdbc.password}" /><propertyname="driverClassName"value="${jdbc.driver}" /><propertyname="maxActive"value="10" /><propertyname="minIdle"value="5" /></bean><!-- sqlsessionfactory --><!-- 让spring管理sqlsessionfactory 使用mybatis和spring整合包中的 --><beanid="sqlSessionFactory"class="org.mybatis.spring.SqlSessionFactoryBean"><!-- 数据库连接池 --><propertyname="dataSource"ref="dataSource" /><!-- 加载mybatis的全局配置文件 --><propertyname="configLocation"value="classpath:mybatis/SqlMapConfig.xml" /></bean><!-- mapper扫描器 --><beanclass="org.mybatis.spring.mapper.MapperScannerConfigurer"><propertyname="basePackage"value="com.taotao.mapper" /></bean>配置sqlSessionFactory给spring来管理
SqlSessionFactoryBean这是一个FactoryBean相信读过spring源码的都知道
org.mybatis.spring.SqlSessionFactoryBean#getObject
@Overridepublic SqlSessionFactorygetObject()throws Exception {if (this.sqlSessionFactory ==null) {//sqlSessionFactory没有构建好,那么就调用afterPropertiesSet
afterPropertiesSet();
}//返回构建好的sqlSessionFactoryreturnthis.sqlSessionFactory;
}org.mybatis.spring.SqlSessionFactoryBean#afterPropertiesSet
@OverridepublicvoidafterPropertiesSet()throws Exception {
notNull(dataSource,"Property 'dataSource' is required");
notNull(sqlSessionFactoryBuilder,"Property 'sqlSessionFactoryBuilder' is required");
.....//构建SqlSessionFactorythis.sqlSessionFactory = buildSqlSessionFactory();
}org.mybatis.spring.SqlSessionFactoryBean#buildSqlSessionFactory
protected SqlSessionFactorybuildSqlSessionFactory()throws IOException {
.....if (this.transactionFactory ==null) {this.transactionFactory =new SpringManagedTransactionFactory();
}
configuration.setEnvironment(new Environment(this.environment,this.transactionFactory,this.dataSource));
......returnthis.sqlSessionFactoryBuilder.build(configuration);
}这段代码可以看出transactionFactory 等于null的时候回去创建一个SpringMngTransFactory
并且把transFactory设置给Environment然后再把Environment设置给configuration,最后
sqlSessionFactoryBuilder.build(configuration);返回sqlSessionFactory
在DefaultSqlSessionFactory#openSessionFromConnection方法中创建了Transaction
private SqlSessionopenSessionFromConnection(ExecutorType execType, Connection connection) {try {boolean autoCommit;try {
autoCommit = connection.getAutoCommit();
}catch (SQLException e) {// Failover to true, as most poor drivers// or databases won't support transactions
autoCommit =true;
}//从configuration中取出environment对象final Environment environment = configuration.getEnvironment();//从environment中取出TransactionFactoryfinal TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);//创建Transactionfinal Transaction tx = transactionFactory.newTransaction(connection);//创建包含事务操作的执行器final Executor executor = configuration.newExecutor(tx, execType);//构建包含执行器的SqlSessionreturnnew DefaultSqlSession(configuration, executor, autoCommit);
}catch (Exception e) {throw ExceptionFactory.wrapException("Error opening session. Cause: " + e, e);
}finally {
ErrorContext.instance().reset();
}
}DefaultSqlSessionFactory#getTransactionFactoryFromEnvironment
private TransactionFactorygetTransactionFactoryFromEnvironment(Environment environment) {//如果没有配置事务工厂，则返回托管事务工厂if (environment ==null || environment.getTransactionFactory() ==null) {returnnew ManagedTransactionFactory();
}return environment.getTransactionFactory();
}这里返回SpringManagedTransactionFactory对象,然后调用
SpringManagedTransactionFactory#newTransaction(javax.sql.DataSource, org.apache.ibatis.session.TransactionIsolationLevel, boolean)
@Overridepublic TransactionnewTransaction(DataSource dataSource, TransactionIsolationLevel level,boolean autoCommit) {returnnew SpringManagedTransaction(dataSource);
}也就是说mybatis的执行事务的事务管理器就切换成了SpringManagedTransaction
我们再看org.mybatis.spring.transaction.SpringManagedTransaction#getConnection
@Overridepublic ConnectiongetConnection()throws SQLException {if (this.connection ==null) {//获取connection
openConnection();
}returnthis.connection;
}privatevoidopenConnection()throws SQLException {//调用DataSourceUtils 拿到数据库连接this.connection = DataSourceUtils.getConnection(this.dataSource);this.autoCommit =this.connection.getAutoCommit();this.isConnectionTransactional = DataSourceUtils.isConnectionTransactional(this.connection,this.dataSource);
.....org.springframework.jdbc.datasource.DataSourceUtils#getConnection
publicstatic ConnectiongetConnection(DataSource dataSource)throws CannotGetJdbcConnectionException {try {return doGetConnection(dataSource);
}catch (SQLException ex) {thrownew CannotGetJdbcConnectionException("Could not get JDBC Connection", ex);
}
}此处进入spring-jdbc的模块代码,猜想:
- spring的@trans事务操作的conn会保存在一个ThreadLocal中
- 当mybatis操作数据库时从这个ThreadLocal中去取conn,这样就可以做到spring来控制mybatis的数据库操作了
下面我们就来验证我们的猜想:
org.springframework.jdbc.datasource.DataSourceUtils#doGetConnection
publicstatic ConnectiondoGetConnection(DataSource dataSource)throws SQLException {
Assert.notNull(dataSource,"No DataSource specified");//获取ConnectionHolder
ConnectionHolder conHolder = (ConnectionHolder) TransactionSynchronizationManager.getResource(dataSource);/**
* conHolder不为空 有链接
*/if (conHolder !=null && (conHolder.hasConnection() || conHolder.isSynchronizedWithTransaction())) {
conHolder.requested();//如果conHolder没有连接if (!conHolder.hasConnection()) {
logger.debug("Fetching resumed JDBC Connection from DataSource");//取出一个连接设置给conHolder
conHolder.setConnection(fetchConnection(dataSource));
}//返回conHolder中的连接return conHolder.getConnection();
}
.....想看怎么获取connHolder
org.springframework.transaction.support.TransactionSynchronizationManager#getResource
@Nullablepublicstatic ObjectgetResource(Object key) {
Object actualKey = TransactionSynchronizationUtils.unwrapResourceIfNecessary(key);//获取ConnectionHolder
Objectvalue = doGetResource(actualKey);
....returnvalue;
}//保存数据库连接的ThreadLocalprivatestaticfinal ThreadLocal<Map<Object, Object>> resources =new NamedThreadLocal<>("Transactional resources");@Nullableprivatestatic ObjectdoGetResource(Object actualKey) {/**
* 从threadlocal <Map<Object, Object>>中取出来当前线程绑定的map
* map里面存的是<dataSource,ConnectionHolder>
*/
Map<Object, Object> map = resources.get();if (map ==null) {returnnull;
}//map中取出来对应dataSource的ConnectionHolder
Object value = map.get(actualKey);// Transparently remove ResourceHolder that was marked as void...if (valueinstanceof ResourceHolder && ((ResourceHolder) value).isVoid()) {
map.remove(actualKey);// Remove entire ThreadLocal if empty...if (map.isEmpty()) {
resources.remove();
}
value =null;
}return value;
}可以看到确实是从ThreadLocal中取出来的conn,而spring自己的事务也是操作的这个ThreadLocal中的conn来进行事务的开启和回滚
然后就取出来connHolder中的conn返回,当取出来的conn为空时候,调用
org.springframework.jdbc.datasource.DataSourceUtils#fetchConnection
privatestatic ConnectionfetchConnection(DataSource dataSource)throws SQLException {//从数据源取出来conn
Connection con = dataSource.getConnection();if (con ==null) {thrownew IllegalStateException("DataSource returned null from getConnection(): " + dataSource);
}return con;
}然后把从数据源取出来的连接返回
到此mybatis的事务是怎么被spring管理的就显而易见了