spring事务之事务挂起和事务恢复源码解读

if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_REQUIRES_NEW) {
	if (debugEnabled) {
		logger.debug("Suspending current transaction, creating new transaction with name [" +
				definition.getName() + "]");
	}
	/**
	 * 这里是挂起事务的操作，挂起事务的话，会把事务管理器中的属性设置为null
	 * ，然后将事务管理器中的属性暂时存储到suspendedResourceHolder中
	 */
	SuspendedResourcesHolder suspendedResources = suspend(transaction);
	try {
		boolean newSynchronization = (getTransactionSynchronization() != SYNCHRONIZATION_NEVER);
		DefaultTransactionStatus status = newTransactionStatus(
				definition, transaction, true, newSynchronization, debugEnabled, suspendedResources);
		// 开启事务
		doBegin(transaction, definition);
		// 将事务绑定到线程中
		prepareSynchronization(status, definition);
		return status;
	}
	catch (RuntimeException | Error beginEx) {
		/**
		 * 如果在开启新的事务的时候，异常了，就会在下面这个方法中，将事务恢复(和上面挂起是相对的)
		 * ，其实就是把suspendResourceHolder中的属性重新赋值到TransactionSynchronizationManager
		 */
		resumeAfterBeginException(transaction, suspendedResources, beginEx);
		throw beginEx;
	}
}

/**
* 这是挂起事务的源码
 * 所谓的事务挂起：就是将当前事务管理器中的相关属性，保存到suspendedResourceHolder中
 */
@Nullable
protected final SuspendedResourcesHolder suspend(@Nullable Object transaction) throws TransactionException {
	/**
	 * 1.如果当前事务是active状态，就将事务挂起，挂起的操作其实也简单
	 * 将当前事务的属性信息暂存到SuspendedResourcesHolder中，然后将当前事务的属性设置为null
	 */
	if (TransactionSynchronizationManager.isSynchronizationActive()) {
		List<TransactionSynchronization> suspendedSynchronizations = doSuspendSynchronization();
		try {
			Object suspendedResources = null;
			if (transaction != null) {
				suspendedResources = doSuspend(transaction);
			}
			/**
			 * 1.1 下面就是挂起事务的操作，将事务同步管理器中的属性置为null
			 * ， 然后将配置信息，存储到suspendedResources中，以便在恢复事务的时候，可以恢复
			 */
			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) {
			/**
			 * 2.如果挂起事务失败，就需要进行回滚，就是将suspendedResourcesHolder
			 * 中的属性重新赋值到TransactionSynchronizationManager中
			 */
			// 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;
	}
}

private void cleanupAfterCompletion(DefaultTransactionStatus status) {
		status.setCompleted();
		if (status.isNewSynchronization()) {
			TransactionSynchronizationManager.clear();
		}
		if (status.isNewTransaction()) {
			doCleanupAfterCompletion(status.getTransaction());
		}
		if (status.getSuspendedResources() != null) {
			if (status.isDebug()) {
				logger.debug("Resuming suspended transaction after completion of inner transaction");
			}
			Object transaction = (status.hasTransaction() ? status.getTransaction() : null);
			resume(transaction, (SuspendedResourcesHolder) status.getSuspendedResources());
		}
	}

protected final void resume(@Nullable Object transaction, @Nullable SuspendedResourcesHolder resourcesHolder)
			throws TransactionException {

		if (resourcesHolder != null) {
			Object suspendedResources = resourcesHolder.suspendedResources;
			if (suspendedResources != null) {
				doResume(transaction, suspendedResources);
			}
			List<TransactionSynchronization> suspendedSynchronizations = resourcesHolder.suspendedSynchronizations;
			if (suspendedSynchronizations != null) {
				TransactionSynchronizationManager.setActualTransactionActive(resourcesHolder.wasActive);
				TransactionSynchronizationManager.setCurrentTransactionIsolationLevel(resourcesHolder.isolationLevel);
				TransactionSynchronizationManager.setCurrentTransactionReadOnly(resourcesHolder.readOnly);
				TransactionSynchronizationManager.setCurrentTransactionName(resourcesHolder.name);
				doResumeSynchronization(suspendedSynchronizations);
			}
		}
	}