七种传播行为的源码解析

Spring 事务七种传播行为

源码

这部分的源码其实比较简单, 只需要着重注意以下几点就可以

• 当前是否存在事务
• 不同的传播行为下需要的动作
  • 使用事务(新建、加入、报错)
  • 不使用事务(挂起、报错)

public abstract class AbstractPlatformTransactionManager 
        implements PlatformTransactionManager, Serializable {

    /**
     * This implementation handles propagation behavior. Delegates to
     * {@code doGetTransaction}, {@code isExistingTransaction}
     * and {@code doBegin}.
     * @see #doGetTransaction
     * @see #isExistingTransaction
     * @see #doBegin
     */
    @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.
            // 事务存在, 根据隔离级别进行处理
            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.
        // 事务不存在的情况下PROPAGATION_MANDATORY行为直接报错
        if (def.getPropagationBehavior() == TransactionDefinition.PROPAGATION_MANDATORY) {
            throw new IllegalTransactionStateException(
                    "No existing transaction found for transaction marked with propagation 'mandatory'");
        }
        // 以下三种传播行为需要开启新事务
        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 {
                boolean newSynchronization = (getTransactionSynchronization() != SYNCHRONIZATION_NEVER);
                DefaultTransactionStatus status = newTransactionStatus(
                        def, transaction, true, newSynchronization, debugEnabled, suspendedResources);
                doBegin(transaction, def);
                prepareSynchronization(status, def);
                return status;
            }
            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);
        }
    }

    /**
     * Create a TransactionStatus for an existing transaction.
     * 已经存在事务的情况下对不同隔离级别的处理
     */
    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);
        }

        // PROPAGATION_REQUIRES_NEW, 将旧的事务挂起, 创建新的status也就是新开一个事务
        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 {
                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;
            }
        }

        // PROPAGATION_NESTED, 开启新事务
        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.
                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);
    }
}