spring事务深入剖析 - JDBC DataSourceTransactionManager 分析

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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();
	}