MyBatis源码分析之——SqlSession会话创建过程

mybatis操作的时候跟数据库的每一次连接,都需要创建一个会话,我们用openSession()方法来创建。这个会话里面需要包含一个Executor用来执行 SQL。Executor又要指定事务类型和执行器的类型。

1.创建Transaction(两种方式)

属性	产生工厂类	产生事务
JDBC	JdbcTransactionFactory	JdbcTransaction
MANAGED	ManagedTransactionFactory	ManagedTransaction

• 如果配置的是 JDBC,则会使用Connection 对象的 commit()、rollback()、close()管理事务。
• 如果配置成MANAGED,会把事务交给容器来管理,比如 JBOSS,Weblogic。

SqlSession sqlSession = sqlSessionFactory.openSession();

public SqlSession openSession() {
//configuration中有默认赋值
protected ExecutorType defaultExecutorType = ExecutorType.SIMPLE
	return openSessionFromDataSource(configuration.getDefaultExecutorType(), null, false);
}

<environments default="development">
	<environment id="development">
		<transactionManager type="JDBC"/>
		<dataSource type="POOLED">
			<property name="driver" value="${driver}"/>
			<property name="url" value="${url}"/>
			<property name="username" value="${username}"/>
			<property name="password" value="${password}"/>
		</dataSource>
	</environment>
</environments>

2.创建Executor

//ExecutorType是SIMPLE,一共有三种SIMPLE(SimpleExecutor)、REUSE(ReuseExecutor)、BATCH(BatchExecutor)
private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
	Transaction tx = null;
	try {
		//xml中的development节点
		final Environment environment = configuration.getEnvironment();
		//type配置的是Jbdc所以生成的是JbdcTransactionFactory工厂类
		final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
		//Jdbc生成JbdcTransactionFactory生成JbdcTransaction
		tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
		//创建CachingExecutor执行器
		final Executor executor = configuration.newExecutor(tx, execType);
		//创建DefaultSqlSession属性包括 Configuration、Executor对象
		return new DefaultSqlSession(configuration, executor, autoCommit);
	} catch (Exception e) {
		closeTransaction(tx); // may have fetched a connection so lets call
		close();
		throw ExceptionFactory.wrapException("Error opening session. Cause: " + e, e);
	} finally {
		ErrorContext.instance().reset();
	}
}