mybatis session 浅析

mybatis session

从源码的角度,去探索mybatis session的内容

    SqlSession sqlSession = sqlSessionFactory.openSession();
    try {
      sqlSession.doXXX
    } finally {
        sqlSession.close();
    }

本节搞清楚两个问题
1. openSession 创建的对象有什么
2. close 关闭了什么

打开会话

直接去 DefaultSqlSessionFactory 去跟进 openSession 的内容:

  public SqlSession openSession() {
    return openSessionFromDataSource(configuration.getDefaultExecutorType(), null, false);
  }

转发给 openSessionFromDataSource

 private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
    Transaction tx = null;
    try {
      final Environment environment = configuration.getEnvironment();
      final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
      tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
      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();
    }
  }

内容如下图

实际上,这里就是一个事务和缓存的管理器,执行时做事务处理和缓存处理

关闭会话

 @Override
  public void close() {
  // 省略无关代码
      executor.close(isCommitOrRollbackRequired(false));
  }

跟进执行器的关闭

// 省略无关代码
    public void close(boolean forceRollback) {
        rollback(forceRollback);
        transaction.close();
    }

     public void rollback(boolean required) throws SQLException {
            clearLocalCache();
            if (required) {
              transaction.rollback();
            }
     }

      public void clearLocalCache() {
           localCache.clear();
           localOutputParameterCache.clear();
      }

不难看出,关闭会话实际上关闭了什么
1. 关闭事务
2. 清空一级缓存

总结

最终得出结论:

mybatis 的session 就是一个事务和缓存的管理器.