事物、源码学习，spring-tx

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

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

    if (txAttr == null || !(tm instanceof CallbackPreferringPlatformTransactionManager)) {
        // Standard transaction demarcation with getTransaction and commit/rollback calls.
        TransactionInfo txInfo = createTransactionIfNecessary(tm, txAttr, joinpointIdentification);
        Object retVal = null;
        try {
            // This is an around advice: Invoke the next interceptor in the chain.
            // This will normally result in a target object being invoked.
            retVal = invocation.proceedWithInvocation();
        }
        catch (Throwable ex) {
            // target invocation exception
            completeTransactionAfterThrowing(txInfo, ex);
            throw ex;
        }
        finally {
            cleanupTransactionInfo(txInfo);
        }
        commitTransactionAfterReturning(txInfo);
        return retVal;
    }

    else {
        // It‘s a CallbackPreferringPlatformTransactionManager: pass a TransactionCallback in.
        try {
            Object result = ((CallbackPreferringPlatformTransactionManager) tm).execute(txAttr,
                    new TransactionCallback<Object>() {
                        @Override
                        public Object doInTransaction(TransactionStatus status) {
                            TransactionInfo txInfo = prepareTransactionInfo(tm, txAttr, joinpointIdentification, status);
                            try {
                                return invocation.proceedWithInvocation();
                            }
                            catch (Throwable ex) {
                                if (txAttr.rollbackOn(ex)) {
                                    // A RuntimeException: will lead to a rollback.
                                    if (ex instanceof RuntimeException) {
                                        throw (RuntimeException) ex;
                                    }
                                    else {
                                        throw new ThrowableHolderException(ex);
                                    }
                                }
                                else {
                                    // A normal return value: will lead to a commit.
                                    return new ThrowableHolder(ex);
                                }
                            }
                            finally {
                                cleanupTransactionInfo(txInfo);
                            }
                        }
                    });

            // Check result: It might indicate a Throwable to rethrow.
            if (result instanceof ThrowableHolder) {
                throw ((ThrowableHolder) result).getThrowable();
            }
            else {
                return result;
            }
        }
        catch (ThrowableHolderException ex) {
            throw ex.getCause();
        }
    }
}

/**
 * Holder to support the {@code currentTransactionStatus()} method,
 * and to support communication between different cooperating advices
 * (e.g. before and after advice) if the aspect involves more than a
 * single method (as will be the case for around advice).
 */
private static final ThreadLocal<TransactionInfo> transactionInfoHolder =
        new NamedThreadLocal<>("Current aspect-driven transaction");

private void bindToThread() {
    // Expose current TransactionStatus, preserving any existing TransactionStatus
    // for restoration after this transaction is complete.
    this.oldTransactionInfo = transactionInfoHolder.get();
    transactionInfoHolder.set(this);
}

private void restoreThreadLocalStatus() {
    // Use stack to restore old transaction TransactionInfo.
    // Will be null if none was set.
    transactionInfoHolder.set(this.oldTransactionInfo);
}

@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
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);
}

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

        try {
            triggerBeforeCompletion(status);

            if (status.hasSavepoint()) {
                if (status.isDebug()) {
                    logger.debug("Rolling back transaction to savepoint");
                }
                status.rollbackToHeldSavepoint();
            }
            else if (status.isNewTransaction()) {
                if (status.isDebug()) {
                    logger.debug("Initiating transaction rollback");
                }
                doRollback(status);
            }
            else {
                // Participating in larger transaction
                if (status.hasTransaction()) {
                    if (status.isLocalRollbackOnly() || isGlobalRollbackOnParticipationFailure()) {
                        if (status.isDebug()) {
                            logger.debug("Participating transaction failed - marking existing transaction as rollback-only");
                        }
                        doSetRollbackOnly(status);
                    }
                    else {
                        if (status.isDebug()) {
                            logger.debug("Participating transaction failed - letting transaction originator decide on rollback");
                        }
                    }
                }
                else {
                    logger.debug("Should roll back transaction but cannot - no transaction available");
                }
                // 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);

        // Raise UnexpectedRollbackException if we had a global rollback-only marker
        if (unexpectedRollback) {
            throw new UnexpectedRollbackException(
                    "Transaction rolled back because it has been marked as rollback-only");
        }
    }
    finally {
        cleanupAfterCompletion(status);
    }
}

@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
protected Object doSuspend(Object transaction) {
    DataSourceTransactionObject txObject = (DataSourceTransactionObject) transaction;
    txObject.setConnectionHolder(null);
    return TransactionSynchronizationManager.unbindResource(obtainDataSource());
}

@Override
protected void doResume(@Nullable Object transaction, Object suspendedResources) {
    TransactionSynchronizationManager.bindResource(obtainDataSource(), suspendedResources);
}

@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 {
        con.commit();
    }
    catch (SQLException ex) {
        throw new TransactionSystemException("Could not commit JDBC transaction", ex);
    }
}

@Override
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);
    }
}

@Override
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();
}

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

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

    // Reset connection.
    Connection con = txObject.getConnectionHolder().getConnection();
    try {
        if (txObject.isMustRestoreAutoCommit()) {
            con.setAutoCommit(true);
        }
        DataSourceUtils.resetConnectionAfterTransaction(
                con, txObject.getPreviousIsolationLevel(), txObject.isReadOnly());
    }
    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();
}

@Nullable
public static Integer prepareConnectionForTransaction(Connection con, @Nullable TransactionDefinition definition)
        throws SQLException {

    Assert.notNull(con, "No Connection specified");

    // Set read-only flag.
    if (definition != null && definition.isReadOnly()) {
        try {
            if (logger.isDebugEnabled()) {
                logger.debug("Setting JDBC Connection [" + con + "] read-only");
            }
            con.setReadOnly(true);
        }
        catch (SQLException | RuntimeException ex) {
            Throwable exToCheck = ex;
            while (exToCheck != null) {
                if (exToCheck.getClass().getSimpleName().contains("Timeout")) {
                    // Assume it‘s a connection timeout that would otherwise get lost: e.g. from JDBC 4.0
                    throw ex;
                }
                exToCheck = exToCheck.getCause();
            }
            // "read-only not supported" SQLException -> ignore, it‘s just a hint anyway
            logger.debug("Could not set JDBC Connection read-only", ex);
        }
    }

    // Apply specific isolation level, if any.
    Integer previousIsolationLevel = null;
    if (definition != null && definition.getIsolationLevel() != TransactionDefinition.ISOLATION_DEFAULT) {
        if (logger.isDebugEnabled()) {
            logger.debug("Changing isolation level of JDBC Connection [" + con + "] to " +
                    definition.getIsolationLevel());
        }
        int currentIsolation = con.getTransactionIsolation();
        if (currentIsolation != definition.getIsolationLevel()) {
            previousIsolationLevel = currentIsolation;
            con.setTransactionIsolation(definition.getIsolationLevel());
        }
    }

    return previousIsolationLevel;
}

......
private static final ThreadLocal<Map<Object, Object>> resources =
        new NamedThreadLocal<>("Transactional resources");
......
public static void bindResource(Object key, Object value) throws IllegalStateException {
    Object actualKey = TransactionSynchronizationUtils.unwrapResourceIfNecessary(key);
    Assert.notNull(value, "Value must not be null");
    Map<Object, Object> map = resources.get();
    // set ThreadLocal Map if none found
    if (map == null) {
        map = new HashMap<>();
        resources.set(map);
    }
    Object oldValue = map.put(actualKey, value);
    // Transparently suppress a ResourceHolder that was marked as void...
    if (oldValue instanceof ResourceHolder && ((ResourceHolder) oldValue).isVoid()) {
        oldValue = null;
    }
    if (oldValue != null) {
        throw new IllegalStateException("Already value [" + oldValue + "] for key [" +
                actualKey + "] bound to thread [" + Thread.currentThread().getName() + "]");
    }
    if (logger.isTraceEnabled()) {
        logger.trace("Bound value [" + value + "] for key [" + actualKey + "] to thread [" +
                Thread.currentThread().getName() + "]");
    }
}