mybatis中怎么创建sqlsession

发布网友 发布时间：2022-04-20 03:53

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热心网友 时间：2022-04-08 04:35

首先， 通过翻阅源码，我们来整理一下mybatis进行持久化操作时重要的几个类：
SqlSessionFactoryBuilder：build方法创建SqlSessionFactory实例。
SqlSessionFactory：创建SqlSession实例的工厂。
SqlSession：用于执行持久化操作的对象，类似于jdbc中的Connection。
SqlSessionTemplate：MyBatis提供的持久层访问模板化的工具，线程安全，可通过构造参数或依赖注入SqlSessionFactory实例。

Hibernate是与MyBatis类似的orm框架，这里与Hibernate进行一下对比，Hibernate中对于connection的管理，是通过以下几个重要的类：
SessionFactory：创建Session实例的工厂，类似于MyBatis中的SqlSessionFactory。
Session：用来执行持久化操作的对象，类似于jdbc中的Connection。
HibernateTemplate：Hibernate提供的持久层访问模板化的工具，线程安全，可通过构造参数或依赖注入SessionFactory实例。

在日常的开发中，我们经常需要这样对MyBatis和Spring进行集成，把sqlSessionFactory交给Spring管理，通常情况下，我们这样配置：

<code class="hljs nimrod"><bean id=<span class="hljs-string">"sqlSessionFactory" class=<span class="hljs-string">"org.mybatis.spring.SqlSessionFactoryBean">

<property name=<span class="hljs-string">"dataSource" <span class="hljs-keyword">ref=<span class="hljs-string">"dataSource" />
</bean></span></span></span></span></span></code>

通过上面的配置，Spring将自动创建一个SqlSessionFactory对象，其中使用到了org.mybatis.spring.SqlSessionFactoryBean，其 是MyBatis为Spring提供的用于创建SqlSessionFactory的类，将在Spring应用程序的上下文建议一下可共享的 MyBatis SqlSessionFactory实例，我们可以通过依赖注入将SqlSessionFactory传递给MyBatis的一些接口。

如果通过Spring进行事务的管理，我们需要增加Spring注解的事务管理机制，如下配置：

<code class="hljs nimrod"><bean id=<span class="hljs-string">"transactionManager" class=<span class="hljs-string">"org.springframework.jdbc.datasource.DataSourceTransactionManager">
<property name=<span class="hljs-string">"dataSource" <span class="hljs-keyword">ref=<span class="hljs-string">"dataSource" />
</bean>

<tx:annotation-driven/></span></span></span></span></span></code>

这样，我们就可以使用Spring @Transactional注解，进行事务的控制，表明所注释的方法应该在一个事务中运行。 Spring将在事务成功完成后提交事务，在事务发生错误时进行异常回滚，而且，Spring会将产生的MyBatis异常转换成适当的 DataAccessExceptions，从而提供具体的异常信息。

下面，我们通过分析SqlSessionUtils中getSession的源码，来详细的了解一下sqlSession的产生过程，源码如下：

<code class="hljs d"><span class="hljs-keyword">public <span class="hljs-keyword">static SqlSession getSqlSession(SqlSessionFactory sessionFactory, ExecutorType executorType, PersistenceExceptionTranslator exceptionTranslator) {

notNull(sessionFactory, <span class="hljs-string">"No SqlSessionFactory specified");
notNull(executorType, <span class="hljs-string">"No ExecutorType specified");

SqlSessionHolder holder = (SqlSessionHolder) getResource(sessionFactory);

<span class="hljs-keyword">if (holder != <span class="hljs-literal">null && holder.isSynchronizedWithTransaction()) {
<span class="hljs-keyword">if (holder.getExecutorType() != executorType) {
<span class="hljs-keyword">throw <span class="hljs-keyword">new TransientDataAccessResourceException(<span class="hljs-string">"Cannot change the ExecutorType when there is an existing transaction");
}

holder.requested();

<span class="hljs-keyword">if (logger.isDebugEnabled()) {
logger.<span class="hljs-keyword">debug(<span class="hljs-string">"Fetched SqlSession [" + holder.getSqlSession() + <span class="hljs-string">"] from current transaction");
}

<span class="hljs-keyword">return holder.getSqlSession();
}

<span class="hljs-keyword">if (logger.isDebugEnabled()) {
logger.<span class="hljs-keyword">debug(<span class="hljs-string">"Creating a new SqlSession");
}

SqlSession session = sessionFactory.openSession(executorType);

<span class="hljs-comment">// Register session holder if synchronization is active (i.e. a Spring TX is active)
<span class="hljs-comment">//
<span class="hljs-comment">// Note: The DataSource used by the Environment should be synchronized with the
<span class="hljs-comment">// transaction either through DataSourceTxMgr or another tx synchronization.
<span class="hljs-comment">// Further assume that if an exception is thrown, whatever started the transaction will
<span class="hljs-comment">// handle closing / rolling back the Connection associated with the SqlSession.
<span class="hljs-keyword">if (isSynchronizationActive()) {
Environment environment = sessionFactory.getConfiguration().getEnvironment();

<span class="hljs-keyword">if (environment.getTransactionFactory() instanceof SpringManagedTransactionFactory) {
<span class="hljs-keyword">if (logger.isDebugEnabled()) {
logger.<span class="hljs-keyword">debug(<span class="hljs-string">"Registering transaction synchronization for SqlSession [" + session + <span class="hljs-string">"]");
}

holder = <span class="hljs-keyword">new SqlSessionHolder(session, executorType, exceptionTranslator);
bindResource(sessionFactory, holder);
registerSynchronization(<span class="hljs-keyword">new SqlSessionSynchronization(holder, sessionFactory));
holder.setSynchronizedWithTransaction(<span class="hljs-literal">true);
holder.requested();
} <span class="hljs-keyword">else {
<span class="hljs-keyword">if (getResource(environment.getDataSource()) == <span class="hljs-literal">null) {
<span class="hljs-keyword">if (logger.isDebugEnabled()) {
logger.<span class="hljs-keyword">debug(<span class="hljs-string">"SqlSession [" + session + <span class="hljs-string">"] was not registered for synchronization because DataSource is not transactional");
}
} <span class="hljs-keyword">else {
<span class="hljs-keyword">throw <span class="hljs-keyword">new TransientDataAccessResourceException(
<span class="hljs-string">"SqlSessionFactory must be using a SpringManagedTransactionFactory in order to use Spring transaction synchronization");
}
}
} <span class="hljs-keyword">else {
<span class="hljs-keyword">if (logger.isDebugEnabled()) {
logger.<span class="hljs-keyword">debug(<span class="hljs-string">"SqlSession [" + session + <span class="hljs-string">"] was not registered for synchronization because synchronization is not active");
}
}

<span class="hljs-keyword">return session;
}</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></code>