Mybatis源码细节探究：sqlSessionFactory.openSession()这个方法到底发生了什么？

news/2024/11/19 12:32:17/

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前言

        InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);SqlSession sqlSession = sqlSessionFactory.openSession();

作为一个开发界的菜鸟，当我研究Mybatis的源码的时候，总是好奇，上边这三行代码单当中走过的时候，发生了什么样的事情呢？我们这篇文章只研究openSession这个方法。

sqlSessionFactory.openSession()

public interface SqlSessionFactory {SqlSession openSession();SqlSession openSession(boolean autoCommit);SqlSession openSession(Connection connection);SqlSession openSession(TransactionIsolationLevel level);SqlSession openSession(ExecutorType execType);SqlSession openSession(ExecutorType execType, boolean autoCommit);SqlSession openSession(ExecutorType execType, TransactionIsolationLevel level);SqlSession openSession(ExecutorType execType, Connection connection);Configuration getConfiguration();}

SqlSessionFactory是SqlSession的工厂，各种各样的重载的openSession方法。
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实现类有两个，默认走的都是第一个DefaultSqlSessionFactory

  @Overridepublic SqlSession openSession() {return openSessionFromDataSource(//默认的是SimpleExcutor,configuration.getDefaultExecutorType(), null, false);}

  private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {Transaction tx = null;try {//final可以修饰局部变量//获取Mybatis-config.xml中的Environment标签对应的对象final Environment environment = configuration.getEnvironment();//通过environment获取事务工厂final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);//通过事务工厂和数据源获取事务对象tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);//configuration.newExecutor(事务对象，Executor类型对象)final Executor executor = configuration.newExecutor(tx, execType);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();}}

通过Environment 获取TransactionFactory 对象
通过TransactionFactory和Environment中的DateSource获取Transaction
通过Transaction 和 ExcutorType获取 Executor 对象
通过Executor configuration autoCommit获取SqlSession对象、

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我们可以得出以下结论
1：openSession()默认创建的是DefaultSqlSession对象，而且三个入参是：ExcutorType、TransatinIsolationLevel、AutoCommit
2：默认的Exuecutor是SimpleExecutor
3：Excutor对象是由Configuration创建的，默认void：SimpleExcutor，param：Transaction、ExecutorType