spring事务深入剖析 - JDBC DataSourceTransactionManager 分析

http://blue2048.iteye.com/blog/2176676

首先介绍下DataSourceTransactionObject这个类，它是DataSourceTransactionManager的事务句柄，用于和AbstractPlatformTransactionManager接口方法之间的交互数据传递

 下面介绍DataSourceTransactionManager各个方法，解析见注释

1.  doGetTransaction

//产生一个DataSourceTransactionObject对象，其中持有ConnectionHolder(从ThreadLocale中拿，可能已经存在这个对象)
protected Object doGetTransaction() {
        DataSourceTransactionObject txObject = new DataSourceTransactionObject();
        txObject.setSavepointAllowed(isNestedTransactionAllowed());
        ConnectionHolder conHolder =
            (ConnectionHolder) TransactionSynchronizationManager.getResource(this.dataSource);
        txObject.setConnectionHolder(conHolder, false);
        return txObject;
    }

 

 

2. isExistingTransaction

 

//从DataSourceTransactionObject取出ConnectionHolder对象，判断connection上是否已经开启过事务protected boolean isExistingTransaction(Object transaction) {
        DataSourceTransactionObject txObject = (DataSourceTransactionObject) transaction;
        return (txObject.getConnectionHolder() != null && txObject.getConnectionHolder().isTransactionActive());
    }

 

3. doBegin

    a. 从DataSourceTransactionObject拿出ConnectionHolder

    b. 从ConnectionHolder拿Connection，设置事务的隔离级别，并开启事务

    c. 将ConnectionHolder绑定到当前Connection上，以被嵌套的事务获取(因为JDBC连接池是根据线程绑定Connection的，所有一次嵌套事务中，使用的是同一个Connection)

protected void doBegin(Object transaction, TransactionDefinition definition) {
        DataSourceTransactionObject txObject = (DataSourceTransactionObject) transaction;
        Connection con = null;

        try {
            if (txObject.getConnectionHolder() == null ||
                    txObject.getConnectionHolder().isSynchronizedWithTransaction()) {
                Connection newCon = this.dataSource.getConnection();
                if (logger.isDebugEnabled()) {
                    logger.debug("Acquired Connection [" + newCon + "] for JDBC transaction");
                }
                txObject.setConnectionHolder(new ConnectionHolder(newCon), true);
            }

            txObject.getConnectionHolder().setSynchronizedWithTransaction(true);
            con = txObject.getConnectionHolder().getConnection();

            Integer previousIsolationLevel = DataSourceUtils.prepareConnectionForTransaction(con, definition);
            txObject.setPreviousIsolationLevel(previousIsolationLevel);

            // Switch to manual commit if necessary. This is very expensive in some JDBC drivers,
            // so we don't want to do it unnecessarily (for example if we've explicitly
            // configured the connection pool to set it already).
            if (con.getAutoCommit()) {
                txObject.setMustRestoreAutoCommit(true);
                if (logger.isDebugEnabled()) {
                    logger.debug("Switching JDBC Connection [" + con + "] to manual commit");
                }
                con.setAutoCommit(false);
            }
            txObject.getConnectionHolder().setTransactionActive(true);

            int timeout = determineTimeout(definition);
            if (timeout != TransactionDefinition.TIMEOUT_DEFAULT) {
                txObject.getConnectionHolder().setTimeoutInSeconds(timeout);
            }

            // Bind the session holder to the thread.
            if (txObject.isNewConnectionHolder()) {
                TransactionSynchronizationManager.bindResource(getDataSource(), txObject.getConnectionHolder());
            }
        }

        catch (Exception ex) {
            DataSourceUtils.releaseConnection(con, this.dataSource);
            throw new CannotCreateTransactionException("Could not open JDBC Connection for transaction", ex);
        }
    }

 

 

4. doSuspend 

 

//清除DataSourceTransactionObject和ThreadLocal中存储的ConnectionHolder对象，外部保存ConnectionHolder对象，以备恢复使用
protected Object doSuspend(Object transaction) {
        DataSourceTransactionObject txObject = (DataSourceTransactionObject) transaction;
        txObject.setConnectionHolder(null);
        ConnectionHolder conHolder = (ConnectionHolder)
                TransactionSynchronizationManager.unbindResource(this.dataSource);
        return conHolder;
    }

 

5. doResume

//外部传入ConnectionHolder对象，恢复到ThreadLocal中去
protected void doResume(Object transaction, Object suspendedResources) {
        ConnectionHolder conHolder = (ConnectionHolder) suspendedResources;
        TransactionSynchronizationManager.bindResource(this.dataSource, conHolder);
    }

 

6. doCommit

protected void doCommit(DefaultTransactionStatus status) {
        DataSourceTransactionObject txObject = (DataSourceTransactionObject) status.getTransaction();
        Connection con = txObject.getConnectionHolder().getConnection();
        if (status.isDebug()) {
            logger.debug("Committing JDBC transaction on Connection [" + con + "]");
        }
        try {
            con.commit();
        }
        catch (SQLException ex) {
            throw new TransactionSystemException("Could not commit JDBC transaction", ex);
        }
    }

 

7. doRollback

protected void doRollback(DefaultTransactionStatus status) {
        DataSourceTransactionObject txObject = (DataSourceTransactionObject) status.getTransaction();
        Connection con = txObject.getConnectionHolder().getConnection();
        if (status.isDebug()) {
            logger.debug("Rolling back JDBC transaction on Connection [" + con + "]");
        }
        try {
            con.rollback();
        }
        catch (SQLException ex) {
            throw new TransactionSystemException("Could not roll back JDBC transaction", ex);
        }
    }

 

8. doSetRollbackOnly

protected void doSetRollbackOnly(DefaultTransactionStatus status) {
        DataSourceTransactionObject txObject = (DataSourceTransactionObject) status.getTransaction();
        if (status.isDebug()) {
            logger.debug("Setting JDBC transaction [" + txObject.getConnectionHolder().getConnection() +
                    "] rollback-only");
        }
        txObject.setRollbackOnly();
    }

 

9. doCleanupAfterCompletion

    a. 从ThreadLocal中将ConnectionHolder清除

    b. 回复Connecton之前的AutoCommit和IsolationLevel属性

    c. 释放connection

    d. 清除ConnectHolder相应的对象属性

protected void doCleanupAfterCompletion(Object transaction) {
        DataSourceTransactionObject txObject = (DataSourceTransactionObject) transaction;

        // Remove the connection holder from the thread, if exposed.
        if (txObject.isNewConnectionHolder()) {
            TransactionSynchronizationManager.unbindResource(this.dataSource);
        }

        // Reset connection.
        Connection con = txObject.getConnectionHolder().getConnection();
        try {
            if (txObject.isMustRestoreAutoCommit()) {
                con.setAutoCommit(true);
            }
            DataSourceUtils.resetConnectionAfterTransaction(con, txObject.getPreviousIsolationLevel());
        }
        catch (Throwable ex) {
            logger.debug("Could not reset JDBC Connection after transaction", ex);
        }

        if (txObject.isNewConnectionHolder()) {
            if (logger.isDebugEnabled()) {
                logger.debug("Releasing JDBC Connection [" + con + "] after transaction");
            }
            DataSourceUtils.releaseConnection(con, this.dataSource);
        }

        txObject.getConnectionHolder().clear();
    }