Spring中@Transactional注解到底做了什么（七）

回到上上一章的invokeWithinTransaction方法，我们来看看事物的提交方法commitTransactionAfterReturning

    protected void commitTransactionAfterReturning(@Nullable TransactionInfo txInfo) {
        if (txInfo != null && txInfo.getTransactionStatus() != null) {
            if (logger.isTraceEnabled()) {
                logger.trace("Completing transaction for [" + txInfo.getJoinpointIdentification() + "]");
            }
            txInfo.getTransactionManager().commit(txInfo.getTransactionStatus());
        }
    }

点进commit方法

    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");
        }
        //／如果在事务链中已经被标记回滚，那不会尝试提交事务，直接回滚
        DefaultTransactionStatus defStatus = (DefaultTransactionStatus) status;
        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;
        }
        // 如果没有被标记回滚之类的，这里才真正判断是否提交
        processCommit(defStatus);

可以看到事务不是立刻提交的，还是要做一些校验。

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

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

                // 判断是否有savePoint
                if (status.hasSavepoint()) {
                    if (status.isDebug()) {
                        logger.debug("Releasing transaction savepoint");
                    }
                    unexpectedRollback = status.isGlobalRollbackOnly();
                    // 不提交，仅仅是释放savePoint
                    status.releaseHeldSavepoint();
                }
                // 判断是否是新事务
                else if (status.isNewTransaction()) {
                    if (status.isDebug()) {
                        logger.debug("Initiating transaction commit");
                    }
                    unexpectedRollback = status.isGlobalRollbackOnly();
                    // 这里才真正去提交！
                    doCommit(status);
                }
                else if (isFailEarlyOnGlobalRollbackOnly()) {
                    unexpectedRollback = status.isGlobalRollbackOnly();
                }

                // Throw UnexpectedRollbackException if we have a global rollback-only
                // marker but still didn't get a corresponding exception from commit.
                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;
            }

            // Trigger afterCommit callbacks, with an exception thrown there
            // propagated to callers but the transaction still considered as committed.
            try {
                triggerAfterCommit(status);
            }
            finally {
                triggerAfterCompletion(status, TransactionSynchronization.STATUS_COMMITTED);
            }

        }
        // 清空记录的资源并将挂起的资源恢复
        finally {
            cleanupAfterCompletion(status);
        }
    }

status.hasSavepoint()如果status有savePoint，说明此时的事务是嵌套事务NESTED，这个事务外面还有事务，这里不提交，只是释放保存点。这里也可以看出来NESTED的传播行为了。
status.isNewTransaction()如果是新的事务，才会提交！！，这里如果是子事务，只有PROPAGATION_NESTED状态才会走到这里提交，也说明了此状态子事务提交和外层事务是隔离的

在最后的提交流程，Spring会将事务提交的操作引导至底层数据库连接的API，进行事务提交。
直接看processCommit方法中的doCommit方法

    @Override
    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 {
            //数据库的提交方法
            con.commit();
        }
        catch (SQLException ex) {
            throw new TransactionSystemException("Could not commit JDBC transaction", ex);
        }
    }

从提交的逻辑看，只有status是新事务，才会进行提交
所以事务的提交最后依靠的还是数据库的事务提交方法