<!-- SqlSession实例 -->
<bean id="sessionTemplate" class="org.mybatis.spring.SqlSessionTemplate"destroy-method="close">
<!--当构造函数有多个参数时，可以使用constructor-arg标签的index属性，index属性的值从0开始，这里将sqlsessionFactory作为第一个参数传入-->
<constructor-arg index="0" ref="sqlSessionFactory" /> </bean>

<!-- 将数据源映射到sqlSessionFactory中 -->
<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean"><property name="configLocation" value="classpath:mybatis/mybatis-config.xml" /><property name="dataSource" ref="dataSource" />
</bean>

<!--======= 事务配置 Begin ================= -->
<!-- 事务管理器（由Spring管理MyBatis的事务） -->
<bean id="transactionManager"class="org.springframework.jdbc.datasource.DataSourceTransactionManager"><!-- 关联数据源 --><property name="dataSource" ref="dataSource"></property>
</bean>
<!-- 注解事务 -->
<tx:annotation-driven transaction-manager="transactionManager" />
<!--======= 事务配置 End =================== -->

public class SqlSessionTemplate implements SqlSession {private final SqlSessionFactory sqlSessionFactory;private final ExecutorType executorType;private final SqlSession sqlSessionProxy;private final PersistenceExceptionTranslator exceptionTranslator;public SqlSessionTemplate(SqlSessionFactory sqlSessionFactory) {this(sqlSessionFactory, sqlSessionFactory.getConfiguration().getDefaultExecutorType());}public SqlSessionTemplate(SqlSessionFactory sqlSessionFactory, ExecutorType executorType) {this(sqlSessionFactory, executorType, new MyBatisExceptionTranslator(sqlSessionFactory.getConfiguration().getEnvironment().getDataSource(), true));}public SqlSessionTemplate(SqlSessionFactory sqlSessionFactory, ExecutorType executorType, PersistenceExceptionTranslator exceptionTranslator) {Assert.notNull(sqlSessionFactory, "Property 'sqlSessionFactory' is required");Assert.notNull(executorType, "Property 'executorType' is required");this.sqlSessionFactory = sqlSessionFactory;this.executorType = executorType;this.exceptionTranslator = exceptionTranslator;this.sqlSessionProxy = (SqlSession)Proxy.newProxyInstance(SqlSessionFactory.class.getClassLoader(), new Class[]{SqlSession.class}, new SqlSessionTemplate.SqlSessionInterceptor());}

private class SqlSessionInterceptor implements InvocationHandler {public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {//获取SqlSession(这个SqlSession才是真正使用的，它不是线程安全的)//这个方法可以根据Spring的事物上下文来获取事物范围内的sqlSessionfinal SqlSession sqlSession = SqlSessionUtils.getSqlSession(SqlSessionTemplate.this.sqlSessionFactory,SqlSessionTemplate.this.executorType,SqlSessionTemplate.this.exceptionTranslator);try {//调用真实SqlSession的方法Object result = method.invoke(sqlSession, args);//然后判断一下当前的sqlSession是否有配置Spring事务 如果没有自动commitif (!SqlSessionUtils.isSqlSessionTransactional(sqlSession, SqlSessionTemplate.this.sqlSessionFactory)) {// force commit even on non-dirty sessions because some databases require// a commit/rollback before calling close()sqlSession.commit(true);}//返回执行结果return result;} catch (Throwable t) {//如果出现异常则根据情况转换后抛出Throwable unwrapped = unwrapThrowable(t);if (SqlSessionTemplate.this.exceptionTranslator != null && unwrapped instanceof PersistenceException) {Throwable translated = SqlSessionTemplate.this.exceptionTranslator.translateExceptionIfPossible((PersistenceException) unwrapped);if (translated != null) {unwrapped = translated;}}throw unwrapped;} finally {//关闭sqlSession//它会根据当前的sqlSession是否在Spring的事务上下文当中来执行具体的关闭动作//如果sqlSession被Spring事务管理 则调用holder.released(); 使计数器-1//否则才真正的关闭sqlSessionSqlSessionUtils.closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory);}}}

public static SqlSession getSqlSession(SqlSessionFactory sessionFactory, ExecutorType executorType, PersistenceExceptionTranslator exceptionTranslator) {     //根据sqlSessionFactory从当前线程对应的资源map中获取SqlSessionHolder，当sqlSessionFactory创建了sqlSession，就会在事务管理器中添加一对映射：key为sqlSessionFactory，value为SqlSessionHolder，该类保存sqlSession及执行方式 SqlSessionHolder holder = (SqlSessionHolder) getResource(sessionFactory); //如果holder不为空，且和当前事务同步 if (holder != null && holder.isSynchronizedWithTransaction()) { //hodler保存的执行类型和获取SqlSession的执行类型不一致，就会抛出异常，也就是说在同一个事务中，执行类型不能变化，原因就是同一个事务中同一个sqlSessionFactory创建的sqlSession会被重用 if (holder.getExecutorType() != executorType) { throw new TransientDataAccessResourceException("Cannot change the ExecutorType when there is an existing transaction"); } //增加该holder,也就是同一事务中同一个sqlSessionFactory创建的唯一sqlSession，其引用数增加，被使用的次数增加
      holder.requested(); //返回sqlSession return holder.getSqlSession(); } //如果找不到，则根据执行类型构造一个新的sqlSession SqlSession session = sessionFactory.openSession(executorType); //判断同步是否激活，只要SpringTX被激活，就是true if (isSynchronizationActive()) { //加载环境变量，判断注册的事务管理器是否是SpringManagedTransaction，也就是Spring管理事务 Environment environment = sessionFactory.getConfiguration().getEnvironment(); if (environment.getTransactionFactory() instanceof SpringManagedTransactionFactory) { //如果是，则将sqlSession加载进事务管理的本地线程缓存中 holder = new SqlSessionHolder(session, executorType, exceptionTranslator); //以sessionFactory为key，hodler为value，加入到TransactionSynchronizationManager管理的本地缓存ThreadLocal<Map<Object, Object>> resources中
        bindResource(sessionFactory, holder); //将holder, sessionFactory的同步加入本地线程缓存中ThreadLocal<Set<TransactionSynchronization>> synchronizations registerSynchronization(new SqlSessionSynchronization(holder, sessionFactory)); //设置当前holder和当前事务同步 holder.setSynchronizedWithTransaction(true); //增加引用数
        holder.requested(); } else { if (getResource(environment.getDataSource()) == null) { } else { throw new TransientDataAccessResourceException( "SqlSessionFactory must be using a SpringManagedTransactionFactory in order to use Spring transaction synchronization"); } } } else { } return session; }

public static void closeSqlSession(SqlSession session, SqlSessionFactory sessionFactory) { //其实下面就是判断session是否被Spring事务管理，如果管理就会得到holder  SqlSessionHolder holder = (SqlSessionHolder) getResource(sessionFactory); if ((holder != null) && (holder.getSqlSession() == session)) { //这里释放的作用，不是关闭，只是减少一下引用数，因为后面可能会被复用
      holder.released(); } else { //如果不是被spring管理，那么就不会被Spring去关闭回收，就需要自己close
      session.close(); } }

<!-- 这个配置使全局的映射器启用或禁用 缓存 -->
<setting name="cacheEnabled" value="true" />
<!-- 开启二级缓存开关 -->
<cache/>