Spring 声明式事务源码分析

Spring 的声明式事务实现方式主要有2种，一种为通过使用Spring的< tx:advice >定义事务通知与AOP相关配置实现，另为一种通过@Transactional实现事务管理实现，个人认为本质上其实都一样，就是用定义的注解或者配置信息将目标对象包装起来，拦截对访问目标对象的请求，实现对目标对象访问的增强处理。Spring 使用 TransactionInterceptor 来拦截请求，实现事务处理。

本文使用的 Spring 版本为 5.0.0.RELEASE，看一下 TransactionInterceptor 的内部实现，

/* AOP Alliance MethodInterceptor for declarative transaction
* management using the common Spring transaction infrastructure
*/
public class TransactionInterceptor extends TransactionAspectSupport implements MethodInterceptor, Serializable {
    ……
    public Object invoke(final MethodInvocation invocation) throws Throwable {
        // Work out the target class: may be {@code null}.
        // The TransactionAttributeSource should be passed the target class
        // as well as the method, which may be from an interface.
        Class<?> targetClass = (invocation.getThis() != null ? AopUtils.getTargetClass(invocation.getThis()) : null);

        // Adapt to TransactionAspectSupport's invokeWithinTransaction...
        return invokeWithinTransaction(invocation.getMethod(), targetClass, invocation::proceed);
    }
    ……
}

上述的类注释信息表明此类是声明式事务管理的拦截器，同时该类实现了 MethodInterceptor 接口，因此进入 invoke 方法，内部调用了invokeWithinTransaction 方法，

protected Object invokeWithinTransaction(Method method, @Nullable Class<?> targetClass,
            final InvocationCallback invocation) throws Throwable {

        // If the transaction attribute is null, the method is non-transactional.
        TransactionAttributeSource tas = getTransactionAttributeSource();
        final TransactionAttribute txAttr = (tas != null ? tas.getTransactionAttribute(method, targetClass) : null);
        final PlatformTransactionManager tm = determineTransactionManager(txAttr);
        final String joinpointIdentification = methodIdentification(method, targetClass, txAttr);

        if (txAttr == null || !(tm instanceof CallbackPreferringPlatformTransactionManager)) {
            // 根据具体情况决定是否创建事务
            TransactionInfo txInfo = createTransactionIfNecessary(tm, txAttr, joinpointIdentification);
            Object retVal = null;
            try {
                //执行目标方法    
                retVal = invocation.proceedWithInvocation();
            }
            catch (Throwable ex) {
                // 异常处理
                completeTransactionAfterThrowing(txInfo, ex);
                throw ex;
            }
            finally {
                //清空事务信息
                cleanupTransactionInfo(txInfo);
            }
            //提交事务
            commitTransactionAfterReturning(txInfo);
            return retVal;
        }

        else {
            //编程式事务处理，此处省略
            ……
        }
    }

这个方法整体逻辑还是非常清晰的，首选获取事务属性，然后是针对声明式事务和编程式事务的不同处理，创建事务信息，执行目标方法，最后根据执行结果进行回滚或提交操作，我们先啦分析创建事务的过程。

protected TransactionInfo createTransactionIfNecessary(@Nullable PlatformTransactionManager tm,
            @Nullable TransactionAttribute txAttr, final String joinpointIdentification) {

        // If no name specified, apply method identification as transaction name.
        if (txAttr != null && txAttr.getName() == null) {
            txAttr = new DelegatingTransactionAttribute(txAttr) {
                @Override
                public String getName() {
                    return joinpointIdentification;
                }
            };
        }

        TransactionStatus status = null;
        if (txAttr != null) {
            if (tm != null) {
                //获取事务状态
                status = tm.getTransaction(txAttr);
            }
            else {
                if (logger.isDebugEnabled()) {
                    logger.debug("Skipping transactional joinpoint [" + joinpointIdentification +
                            "] because no transaction manager has been configured");
                }
            }
        }
        //准备一个 TransactionInfo
        return prepareTransactionInfo(tm, txAttr, joinpointIdentification, status);
    }

public final TransactionStatus getTransaction(@Nullable TransactionDefinition definition) throws TransactionException {
        Object transaction = doGetTransaction();

        boolean debugEnabled = logger.isDebugEnabled();

        if (definition == null) {
            definition = new DefaultTransactionDefinition();
        }

        //判断当前线程是否已经存在事务
        if (isExistingTransaction(transaction)) {
            return handleExistingTransaction(definition, transaction, debugEnabled);
        }

        if (definition.getTimeout() < TransactionDefinition.TIMEOUT_DEFAULT) {
            throw new InvalidTimeoutException("Invalid transaction timeout", definition.getTimeout());
        }

        //如果当前线程不存在事务并且事务的传播行为是PROPAGATION_MANDATORY，则抛出异常
        if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_MANDATORY) {
            throw new IllegalTransactionStateException(
                    "No existing transaction found for transaction marked with propagation 'mandatory'");
        }
        else if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_REQUIRED ||
                definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_REQUIRES_NEW ||
                definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_NESTED) {
            //在当前线程不存在事务的前提下，而这三种事务传播行为需要创建新事务，因此执行事务空挂起
            SuspendedResourcesHolder suspendedResources = suspend(null);
            if (debugEnabled) {
                logger.debug("Creating new transaction with name [" + definition.getName() + "]: " + definition);
            }
            try {
                boolean newSynchronization = (getTransactionSynchronization() != SYNCHRONIZATION_NEVER);
                DefaultTransactionStatus status = newTransactionStatus(
                        definition, transaction, true, newSynchronization, debugEnabled, suspendedResources);
                //开启事务      
                doBegin(transaction, definition);
                //同步事务状态
                prepareSynchronization(status, definition);
                return status;
            }
            catch (RuntimeException | Error ex) {
                resume(null, suspendedResources);
                throw ex;
            }
        }
        else {
            if (definition.getIsolationLevel() != TransactionDefinition.ISOLATION_DEFAULT && logger.isWarnEnabled()) {
                logger.warn("Custom isolation level specified but no actual transaction initiated; " +
                        "isolation level will effectively be ignored: " + definition);
            }
            boolean newSynchronization = (getTransactionSynchronization() == SYNCHRONIZATION_ALWAYS);
            return prepareTransactionStatus(definition, null, true, newSynchronization, debugEnabled, null);
        }
    }

    protected Object doGetTransaction() {
        DataSourceTransactionObject txObject = new DataSourceTransactionObject();
        txObject.setSavepointAllowed(isNestedTransactionAllowed());
        //如果当前线程已记录数据库连接，则直接拿来使用
        ConnectionHolder conHolder =
            (ConnectionHolder) TransactionSynchronizationManager.getResource(this.dataSource);
        //此处的false 表示此连接不是新创建的
        txObject.setConnectionHolder(conHolder, false);
        return txObject;
    }

    protected boolean isExistingTransaction(Object transaction) {
        //判断当前线程是否存在事务就是判断记录的数据库连接是否为空并且transactionActive状态为true。
        DataSourceTransactionObject txObject = (DataSourceTransactionObject) transaction;
        return (txObject.getConnectionHolder() != null && txObject.getConnectionHolder().isTransactionActive());
    }

    private TransactionStatus handleExistingTransaction(
            TransactionDefinition definition, Object transaction, boolean debugEnabled)
            throws TransactionException {
        //如果当前线程存在事务并且事务的传播行为是PROPAGATION_NEVER，则抛出异常
        if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_NEVER) {
            throw new IllegalTransactionStateException(
                    "Existing transaction found for transaction marked with propagation 'never'");
        }

        if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_NOT_SUPPORTED) {
            if (debugEnabled) {
                logger.debug("Suspending current transaction");
            }
            //如果当前线程存在事务并且事务的传播行为是PROPAGATION_NOT_SUPPORTED，则将当前事务挂起。
            Object suspendedResources = suspend(transaction);
            boolean newSynchronization = (getTransactionSynchronization() == SYNCHRONIZATION_ALWAYS);
            return prepareTransactionStatus(
                    definition, null, false, newSynchronization, debugEnabled, suspendedResources);
        }

        if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_REQUIRES_NEW) {
            if (debugEnabled) {
                logger.debug("Suspending current transaction, creating new transaction with name [" +
                        definition.getName() + "]");
            }
            //如果当前线程存在事务并且事务的传播行为是PROPAGATION_REQUIRES_NEW，则将当前事务挂起，同时建立新事务。
            SuspendedResourcesHolder suspendedResources = suspend(transaction);
            try {
                boolean newSynchronization = (getTransactionSynchronization() != SYNCHRONIZATION_NEVER);
                DefaultTransactionStatus status = newTransactionStatus(
                        definition, transaction, true, newSynchronization, debugEnabled, suspendedResources);
                doBegin(transaction, definition);
                prepareSynchronization(status, definition);
                return status;
            }
            catch (RuntimeException | Error beginEx) {
                resumeAfterBeginException(transaction, suspendedResources, beginEx);
                throw beginEx;
            }
        }

        if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_NESTED) {
            if (!isNestedTransactionAllowed()) {
                throw new NestedTransactionNotSupportedException(
                        "Transaction manager does not allow nested transactions by default - " +
                        "specify 'nestedTransactionAllowed' property with value 'true'");
            }
            if (debugEnabled) {
                logger.debug("Creating nested transaction with name [" + definition.getName() + "]");
            }
            if (useSavepointForNestedTransaction()) {
                // Create savepoint within existing Spring-managed transaction,
                // through the SavepointManager API implemented by TransactionStatus.
                // Usually uses JDBC 3.0 savepoints. Never activates Spring synchronization.
                DefaultTransactionStatus status =
                        prepareTransactionStatus(definition, transaction, false, false, debugEnabled, null);
                //如果当前线程存在事务并且事务的传播行为是PROPAGATION_NESTED，则创建还原点。
                status.createAndHoldSavepoint();
                return status;
            }
            else {
                // Nested transaction through nested begin and commit/rollback calls.
                // Usually only for JTA: Spring synchronization might get activated here
                // in case of a pre-existing JTA transaction.
                boolean newSynchronization = (getTransactionSynchronization() != SYNCHRONIZATION_NEVER);
                DefaultTransactionStatus status = newTransactionStatus(
                        definition, transaction, true, newSynchronization, debugEnabled, null);
                doBegin(transaction, definition);
                prepareSynchronization(status, definition);
                return status;
            }
        }

        // Assumably PROPAGATION_SUPPORTS or PROPAGATION_REQUIRED.
        if (debugEnabled) {
            logger.debug("Participating in existing transaction");
        }
        if (isValidateExistingTransaction()) {
            if (definition.getIsolationLevel() != TransactionDefinition.ISOLATION_DEFAULT) {
                Integer currentIsolationLevel = TransactionSynchronizationManager.getCurrentTransactionIsolationLevel();
                if (currentIsolationLevel == null || currentIsolationLevel != definition.getIsolationLevel()) {
                    Constants isoConstants = DefaultTransactionDefinition.constants;
                    throw new IllegalTransactionStateException("Participating transaction with definition [" +
                            definition + "] specifies isolation level which is incompatible with existing transaction: " +
                            (currentIsolationLevel != null ?
                                    isoConstants.toCode(currentIsolationLevel, DefaultTransactionDefinition.PREFIX_ISOLATION) :
                                    "(unknown)"));
                }
            }
            if (!definition.isReadOnly()) {
                if (TransactionSynchronizationManager.isCurrentTransactionReadOnly()) {
                    throw new IllegalTransactionStateException("Participating transaction with definition [" +
                            definition + "] is not marked as read-only but existing transaction is");
                }
            }
        }
        boolean newSynchronization = (getTransactionSynchronization() != SYNCHRONIZATION_NEVER);
        return prepareTransactionStatus(definition, transaction, false, newSynchronization, debugEnabled, null);
    }

这里重点看一下在已有事务的前提下，如何处理 PROPAGATION_REQUIRES_NEW 传播行为。此行为会开启一个新事务并挂起原事务，因此此处需要一个新的数据库连接，

    protected final SuspendedResourcesHolder suspend(@Nullable Object transaction) throws TransactionException {
        if (TransactionSynchronizationManager.isSynchronizationActive()) {
            List<TransactionSynchronization> suspendedSynchronizations = doSuspendSynchronization();
            try {
                Object suspendedResources = null;
                if (transaction != null) {
                    suspendedResources = doSuspend(transaction);
                }
                String name = TransactionSynchronizationManager.getCurrentTransactionName();
                TransactionSynchronizationManager.setCurrentTransactionName(null);
                boolean readOnly = TransactionSynchronizationManager.isCurrentTransactionReadOnly();
                TransactionSynchronizationManager.setCurrentTransactionReadOnly(false);
                Integer isolationLevel = TransactionSynchronizationManager.getCurrentTransactionIsolationLevel();
                TransactionSynchronizationManager.setCurrentTransactionIsolationLevel(null);
                boolean wasActive = TransactionSynchronizationManager.isActualTransactionActive();
                TransactionSynchronizationManager.setActualTransactionActive(false);
                return new SuspendedResourcesHolder(
                        suspendedResources, suspendedSynchronizations, name, readOnly, isolationLevel, wasActive);
            }
            catch (RuntimeException | Error ex) {
                // doSuspend failed - original transaction is still active...
                doResumeSynchronization(suspendedSynchronizations);
                throw ex;
            }
        }
        else if (transaction != null) {
            // Transaction active but no synchronization active.
            Object suspendedResources = doSuspend(transaction);
            return new SuspendedResourcesHolder(suspendedResources);
        }
        else {
            // Neither transaction nor synchronization active.
            return null;
        }
    }

    protected Object doSuspend(Object transaction) {
        DataSourceTransactionObject txObject = (DataSourceTransactionObject) transaction;
        txObject.setConnectionHolder(null);
        ConnectionHolder conHolder = (ConnectionHolder)
                TransactionSynchronizationManager.unbindResource(this.dataSource);
        return conHolder;
    }

suspend挂起操作主要目的是将当前connectionHolder置为null，保存原有事务信息，以便于后续恢复原有事务，并将当前正在进行的事务信息进行重置。

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

这里首先获取数据库连接，如果是新事务需要获取新一个新的数据库连接，并为其设置了隔离级别、是否只读等属性，剩下的就是将事务信息记录到当前线程中，

    protected void prepareSynchronization(DefaultTransactionStatus status, TransactionDefinition definition) {
        if (status.isNewSynchronization()) {
            TransactionSynchronizationManager.setActualTransactionActive(status.hasTransaction());
            TransactionSynchronizationManager.setCurrentTransactionIsolationLevel(
                    definition.getIsolationLevel() != TransactionDefinition.ISOLATION_DEFAULT ?
                            definition.getIsolationLevel() : null);
            TransactionSynchronizationManager.setCurrentTransactionReadOnly(definition.isReadOnly());
            TransactionSynchronizationManager.setCurrentTransactionName(definition.getName());
            TransactionSynchronizationManager.initSynchronization();
        }
    }

记录事务状态并返回事务信息，

    protected TransactionInfo prepareTransactionInfo(@Nullable PlatformTransactionManager tm,
            @Nullable TransactionAttribute txAttr, String joinpointIdentification,
            @Nullable TransactionStatus status) {

        TransactionInfo txInfo = new TransactionInfo(tm, txAttr, joinpointIdentification);
        if (txAttr != null) {
            // 记录事务状态
            txInfo.newTransactionStatus(status);
        }
        else {
            ……
        }

        //将事务绑定至当前线程
        txInfo.bindToThread();
        return txInfo;
    }

创建完事务后，就是执行目标业务方法了，根据执行结果的不同做提交或回滚操作，我们先看一下回滚操作，

    protected void completeTransactionAfterThrowing(@Nullable TransactionInfo txInfo, Throwable ex) {
        //如果不存在事务，自然不需要回滚处理
        if (txInfo != null && txInfo.getTransactionStatus() != null) {
            if (logger.isTraceEnabled()) {
                logger.trace("Completing transaction for [" + txInfo.getJoinpointIdentification() +
                        "] after exception: " + ex);
            }
            判断是否需要回滚，回滚条件默认为RuntimeException或Error，我们也可以自行配置。
            if (txInfo.transactionAttribute != null && txInfo.transactionAttribute.rollbackOn(ex)) {
                try {
                    txInfo.getTransactionManager().rollback(txInfo.getTransactionStatus());
                }
                catch (TransactionSystemException ex2) {
                    logger.error("Application exception overridden by rollback exception", ex);
                    ex2.initApplicationException(ex);
                    throw ex2;
                }
                catch (RuntimeException ex2) {
                    logger.error("Application exception overridden by rollback exception", ex);
                    throw ex2;
                }
                catch (Error err) {
                    logger.error("Application exception overridden by rollback error", ex);
                    throw err;
                }
            }
            else {
                // We don't roll back on this exception.
                // Will still roll back if TransactionStatus.isRollbackOnly() is true.
                try {
                    txInfo.getTransactionManager().commit(txInfo.getTransactionStatus());
                }
                catch (TransactionSystemException ex2) {
                    logger.error("Application exception overridden by commit exception", ex);
                    ex2.initApplicationException(ex);
                    throw ex2;
                }
                catch (RuntimeException ex2) {
                    logger.error("Application exception overridden by commit exception", ex);
                    throw ex2;
                }
                catch (Error err) {
                    logger.error("Application exception overridden by commit error", ex);
                    throw err;
                }
            }
        }
    }

    public final void rollback(TransactionStatus status) throws TransactionException {
        if (status.isCompleted()) {
            throw new IllegalTransactionStateException(
                    "Transaction is already completed - do not call commit or rollback more than once per transaction");
        }

        DefaultTransactionStatus defStatus = (DefaultTransactionStatus) status;
        processRollback(defStatus, false);
    }

    private void processRollback(DefaultTransactionStatus status, boolean unexpected) {
        try {
            boolean unexpectedRollback = unexpected;

            try {
                triggerBeforeCompletion(status);

                if (status.hasSavepoint()) {
                    ……
                    //如果存在保存点，则回退到保存点
                    status.rollbackToHeldSavepoint();
                }
                else if (status.isNewTransaction()) {
                    ……
                    //如果是新事物，则回滚
                    doRollback(status);
                }
                else {
                    // Participating in larger transaction
                    if (status.hasTransaction()) {
                        if (status.isLocalRollbackOnly() || isGlobalRollbackOnParticipationFailure()) {
                            ……
                            //当前事务不是独立事务，则需要等到事务链执行完毕才能回滚
                            doSetRollbackOnly(status);
                        }
                        else {
                            ……
                            }
                        }
                    }
                    else {
                        ……
                    }
                    // Unexpected rollback only matters here if we're asked to fail early
                    if (!isFailEarlyOnGlobalRollbackOnly()) {
                        unexpectedRollback = false;
                    }
                }
            }
            catch (RuntimeException | Error ex) {
                triggerAfterCompletion(status, TransactionSynchronization.STATUS_UNKNOWN);
                throw ex;
            }

            triggerAfterCompletion(status, TransactionSynchronization.STATUS_ROLLED_BACK);

            if (unexpectedRollback) {
                throw new UnexpectedRollbackException(
                        "Transaction rolled back because it has been marked as rollback-only");
            }
        }
        finally {
            cleanupAfterCompletion(status);
        }
    }

保存点一般用于嵌入式事务，内嵌事务的回滚不会引起外部事务的回滚。新事务则获取当前线程的数据库连接并调用其rollback方法进行回滚，使用的是底层数据库连接提供的API，结束后还有一个清理和恢复挂起事务的操作。最后再来一下事务的提交处理，

    protected void commitTransactionAfterReturning(@Nullable TransactionInfo txInfo) {
        if (txInfo != null && txInfo.getTransactionStatus() != null) {
            ……
            txInfo.getTransactionManager().commit(txInfo.getTransactionStatus());
        }
    }

    public final void commit(TransactionStatus status) throws TransactionException {
        if (status.isCompleted()) {
            throw new IllegalTransactionStateException(
                    "Transaction is already completed - do not call commit or rollback more than once per transaction");
        }

        DefaultTransactionStatus defStatus = (DefaultTransactionStatus) status;

        //上文分析回滚流程中我们提到了如果当前事务不是独立的事务，也没有保存点，在回滚的时候只是设置一个回滚标记，由外部事务提交时统一进行整体事务的回滚。
        if (defStatus.isLocalRollbackOnly()) {
            if (defStatus.isDebug()) {
                logger.debug("Transactional code has requested rollback");
            }
            processRollback(defStatus, false);
            return;
        }

        if (!shouldCommitOnGlobalRollbackOnly() && defStatus.isGlobalRollbackOnly()) {
            if (defStatus.isDebug()) {
                logger.debug("Global transaction is marked as rollback-only but transactional code requested commit");
            }
            processRollback(defStatus, true);
            return;
        }

        processCommit(defStatus);
    }

    private void processCommit(DefaultTransactionStatus status) throws TransactionException {
        try {
            boolean beforeCompletionInvoked = false;

            try {
                boolean unexpectedRollback = false;
                prepareForCommit(status);
                triggerBeforeCommit(status);
                triggerBeforeCompletion(status);
                beforeCompletionInvoked = true;

                if (status.hasSavepoint()) {
                    if (status.isDebug()) {
                        logger.debug("Releasing transaction savepoint");
                    }
                    unexpectedRollback = status.isGlobalRollbackOnly();
                    status.releaseHeldSavepoint();
                }
                else if (status.isNewTransaction()) {
                    if (status.isDebug()) {
                        logger.debug("Initiating transaction commit");
                    }
                    unexpectedRollback = status.isGlobalRollbackOnly();
                    doCommit(status);
                }
                else if (isFailEarlyOnGlobalRollbackOnly()) {
                    unexpectedRollback = status.isGlobalRollbackOnly();
                }

                if (unexpectedRollback) {
                    throw new UnexpectedRollbackException(
                            "Transaction silently rolled back because it has been marked as rollback-only");
                }
            }
            catch (UnexpectedRollbackException ex) {
                // can only be caused by doCommit
                triggerAfterCompletion(status, TransactionSynchronization.STATUS_ROLLED_BACK);
                throw ex;
            }
            catch (TransactionException ex) {
                // can only be caused by doCommit
                if (isRollbackOnCommitFailure()) {
                    doRollbackOnCommitException(status, ex);
                }
                else {
                    triggerAfterCompletion(status, TransactionSynchronization.STATUS_UNKNOWN);
                }
                throw ex;
            }
            catch (RuntimeException | Error ex) {
                if (!beforeCompletionInvoked) {
                    triggerBeforeCompletion(status);
                }
                doRollbackOnCommitException(status, ex);
                throw ex;
            }

            try {
                triggerAfterCommit(status);
            }
            finally {
                triggerAfterCompletion(status, TransactionSynchronization.STATUS_COMMITTED);
            }

        }
        finally {
            cleanupAfterCompletion(status);
        }
    }

提交操作其实很简单，就是调用数据库连接底层API的commit方法。