mybatis0090-SqlSessionFactory创建SqlSession

深碍√TFBOYSˉ_ 2022-01-27 10:59 337阅读 0赞

### 文章目录 ###

*   *   *  1. 创建SqlSession
         *  2. DefaultSqlSessionFactory的openSessionFromDataSource
         *  3. 执行流程

### 1. 创建SqlSession ###

SqlSession sqlSession = sqlSessionFactory.openSession();

### 2. DefaultSqlSessionFactory的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();
        }
      }

创建SqlSession的过程，其实是对jdbc的Connection的一次再封装，Connection–>Statement–>Executor–>SqlSeesion  
Executor有三种类型：SIMPLE 就是普通的执行器；REUSE 执行器会重用预处理语句（prepared statements）； BATCH 执行器将重用语句并执行批量更新。configuration.newExecutor(tx, execType)会根据execType创建出其中一种执行器(默认是ExecutorType.SIMPLE)，如下：

public Executor newExecutor(Transaction transaction, ExecutorType executorType) { 
        executorType = executorType == null ? defaultExecutorType : executorType;
        executorType = executorType == null ? ExecutorType.SIMPLE : executorType;
        Executor executor;
        if (ExecutorType.BATCH == executorType) { 
          executor = new BatchExecutor(this, transaction);
        } else if (ExecutorType.REUSE == executorType) { 
          executor = new ReuseExecutor(this, transaction);
        } else { 
          executor = new SimpleExecutor(this, transaction);
        }
        if (cacheEnabled) { 
          executor = new CachingExecutor(executor);
        }
        executor = (Executor) interceptorChain.pluginAll(executor);
        return executor;
      }

最后，将执行器和配置对象封装到SqlSession中返回，所以对于使用mybatis把SqlSession当作Connection来使用即可。

### 3. 执行流程 ###

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