스프링의 트랜잭션 관리자

@Override
	public final TransactionStatus getTransaction(@Nullable TransactionDefinition definition)
			throws TransactionException {

		// Use defaults if no transaction definition given.
		TransactionDefinition def = (definition != null ? definition : TransactionDefinition.withDefaults());

		Object transaction = doGetTransaction();
		boolean debugEnabled = logger.isDebugEnabled();

		if (isExistingTransaction(transaction)) {
			// Existing transaction found -> check propagation behavior to find out how to behave.
			return handleExistingTransaction(def, transaction, debugEnabled);
		}

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

		// No existing transaction found -> check propagation behavior to find out how to proceed.
		if (def.getPropagationBehavior() == TransactionDefinition.PROPAGATION_MANDATORY) {
			throw new IllegalTransactionStateException(
					"No existing transaction found for transaction marked with propagation 'mandatory'");
		}
		else if (def.getPropagationBehavior() == TransactionDefinition.PROPAGATION_REQUIRED ||
				def.getPropagationBehavior() == TransactionDefinition.PROPAGATION_REQUIRES_NEW ||
				def.getPropagationBehavior() == TransactionDefinition.PROPAGATION_NESTED) {
			SuspendedResourcesHolder suspendedResources = suspend(null);
			if (debugEnabled) {
				logger.debug("Creating new transaction with name [" + def.getName() + "]: " + def);
			}
			try {
				return startTransaction(def, transaction, debugEnabled, suspendedResources);
			}
			catch (RuntimeException | Error ex) {
				resume(null, suspendedResources);
				throw ex;
			}
		}
		else {
			// Create "empty" transaction: no actual transaction, but potentially synchronization.
			if (def.getIsolationLevel() != TransactionDefinition.ISOLATION_DEFAULT && logger.isWarnEnabled()) {
				logger.warn("Custom isolation level specified but no actual transaction initiated; " +
						"isolation level will effectively be ignored: " + def);
			}
			boolean newSynchronization = (getTransactionSynchronization() == SYNCHRONIZATION_ALWAYS);
			return prepareTransactionStatus(def, null, true, newSynchronization, debugEnabled, null);
		}
	}

@Override
protected Object doGetTransaction() {
  DataSourceTransactionObject txObject = new DataSourceTransactionObject();
  txObject.setSavepointAllowed(isNestedTransactionAllowed());
  ConnectionHolder conHolder =
      (ConnectionHolder) TransactionSynchronizationManager.getResource(obtainDataSource());
  txObject.setConnectionHolder(conHolder, false);
  return txObject;
}

public Savepoint createSavepoint() throws SQLException {
		this.savepointCounter++;
		return getConnection().setSavepoint(SAVEPOINT_NAME_PREFIX + this.savepointCounter);
	}

private TransactionStatus handleExistingTransaction(
			TransactionDefinition definition, Object transaction, boolean debugEnabled)
			throws TransactionException {

		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");
			}
			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() + "]");
			}
			SuspendedResourcesHolder suspendedResources = suspend(transaction);
			try {
				return startTransaction(definition, transaction, debugEnabled, suspendedResources);
			}
			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);
				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.
				return startTransaction(definition, transaction, debugEnabled, null);
			}
		}

		// 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);
	}

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

  try {
    if (!txObject.hasConnectionHolder() ||
        txObject.getConnectionHolder().isSynchronizedWithTransaction()) {
      Connection newCon = obtainDataSource().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);
    txObject.setReadOnly(definition.isReadOnly());

    // 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);
    }

    prepareTransactionalConnection(con, definition);
    txObject.getConnectionHolder().setTransactionActive(true);

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

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

  catch (Throwable ex) {
    if (txObject.isNewConnectionHolder()) {
      DataSourceUtils.releaseConnection(con, obtainDataSource());
      txObject.setConnectionHolder(null, false);
    }
    throw new CannotCreateTransactionException("Could not open JDBC Connection for transaction", ex);
  }
}

@Override
	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;
		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);
	}