项目开发-iBatis事务源码之开启新事务

      iBatis事务源码流程整理如下。主要包括事务的使用以及各个方法的调用过程。

   iBatis的事务使用

     iBatis只有对单个的增、删、改操作添加了默认事务处理过程，如果客户端没有开启事务，那么就为这些操作自动添加事务，以保证这些修改操作会被提交。因此，客户端多条语句的原子操作，需要自己调用iBatis的事务方法，将这些操作封装在事务中来实现。典型的事务使用代码如下：

 * try { *   <b>sqlMap.startTransaction()</b> *   Employee emp2 = new Employee(); *   // ...set emp2 data *   Integer generatedKey = (Integer) <b>sqlMap.insert ("insertEmployee", emp2)</b>; *   emp2.setFavouriteColour ("green"); *   <b>sqlMap.update("updateEmployee", emp2)</b>; *   <b>sqlMap.commitTransaction()</b>; * } finally { *   <b>sqlMap.endTransaction()</b>; * }

   这是SqlMapClient类的注释部分，该类的注释本质上就是iBatis的SqlMapClient的API文档。例如：开户流程中需要保证账户和人员信息的原子性。示例如下

SqlMapClient client = SimpleExample.getInstance();try {client.startTransaction();SimpleExample.insertPerson(p);SimpleExample.insertAccount(account);client.commitTransaction();} catch (SQLException execption) {}finally{try {client.endTransaction();} catch (SQLException e) {e.printStackTrace();}}

  startTransaction

   1）SqlMapClientImpl提供的startTransaction()方法

  public void startTransaction() throws SQLException {    getLocalSqlMapSession().startTransaction();  }

  protected SqlMapSessionImpl getLocalSqlMapSession() {    SqlMapSessionImpl sqlMapSession = (SqlMapSessionImpl) localSqlMapSession.get();    if (sqlMapSession == null || sqlMapSession.isClosed()) {      sqlMapSession = new SqlMapSessionImpl(this);      localSqlMapSession.set(sqlMapSession);    }    return sqlMapSession;  }

   2）SqlMapSessionImpl类的startTransaction()

  public SqlMapSessionImpl(SqlMapClientImpl client) {    this.delegate = client.getDelegate();    this.sessionScope = this.delegate.beginSessionScope();    this.sessionScope.setSqlMapClient(client);    this.sessionScope.setSqlMapExecutor(client);    this.sessionScope.setSqlMapTxMgr(client);    this.closed = false;  }

  public void startTransaction() throws SQLException {    delegate.startTransaction(sessionScope);  }

   3）SqlMapExecutorDelegate的startTransaction()

  public void startTransaction(SessionScope sessionScope) throws SQLException {    try {      txManager.begin(sessionScope);    } catch (TransactionException e) {      throw new NestedSQLException("Could not start transaction.  Cause: " + e, e);    }  }

   4）TransactionManager的begin()方法

  public void begin(SessionScope sessionScope, int transactionIsolation) throws SQLException, TransactionException {    Transaction trans = sessionScope.getTransaction();    TransactionState state = sessionScope.getTransactionState();    if (state == TransactionState.STATE_STARTED) {      throw new TransactionException("TransactionManager could not start a new transaction.  " +          "A transaction is already started.");    } else if (state == TransactionState.STATE_USER_PROVIDED) {      throw new TransactionException("TransactionManager could not start a new transaction.  " +          "A user provided connection is currently being used by this session.  " +          "The calling .setUserConnection (null) will clear the user provided transaction.");    }    trans = config.newTransaction(transactionIsolation);    sessionScope.setCommitRequired(false);    sessionScope.setTransaction(trans);    sessionScope.setTransactionState(TransactionState.STATE_STARTED);  }

   5）TransactionConfig的newTransaction()代码

  public Transaction newTransaction(int transactionIsolation) throws SQLException, TransactionException {    return new JdbcTransaction(dataSource, transactionIsolation);  }

     该操作执行完成后，SqlMapSessionImpl的属性SessionScope中存储了当前会话的事务的信息：当前新建的事务对象，以及事务的状态（新建状态）和提交标识（false）。