Spring 事务模板方法设计模式

接上一篇文章

上一篇讲到了doGetTransaction方法

一、模板方法设计模式

这里涉及到了一个经典的设计模式：模板方法

如下图：

AbstractPlatformTransactionManager实现了PlatformTranscationManager接口

DatasourceTransactionManager,HibernateTransactionManager等继承了AbstractPlatformTransactionManager类

AbstractPlatformTransactionManager类中定义了事务处理的若干方法。 其中获得事务，提交事务，回滚事务由具体的子类实现。

二、进入doGetTransaction的其中一个实现类Hibernate3中的HibernateTransactionManager 类

进入doGetTransaction方法

	@Override
	protected Object doGetTransaction() {
		HibernateTransactionObject txObject = new HibernateTransactionObject();
		txObject.setSavepointAllowed(isNestedTransactionAllowed());

		SessionHolder sessionHolder =
				(SessionHolder) TransactionSynchronizationManager.getResource(getSessionFactory());
		if (sessionHolder != null) {
			if (logger.isDebugEnabled()) {
				logger.debug("Found thread-bound Session [" +
						SessionFactoryUtils.toString(sessionHolder.getSession()) + "] for Hibernate transaction");
			}
			txObject.setSessionHolder(sessionHolder);
		}
		else if (this.hibernateManagedSession) {
			try {
				Session session = getSessionFactory().getCurrentSession();
				if (logger.isDebugEnabled()) {
					logger.debug("Found Hibernate-managed Session [" +
							SessionFactoryUtils.toString(session) + "] for Spring-managed transaction");
				}
				txObject.setExistingSession(session);
			}
			catch (HibernateException ex) {
				throw new DataAccessResourceFailureException(
						"Could not obtain Hibernate-managed Session for Spring-managed transaction", ex);
			}
		}

		if (getDataSource() != null) {
			ConnectionHolder conHolder = (ConnectionHolder)
					TransactionSynchronizationManager.getResource(getDataSource());
			txObject.setConnectionHolder(conHolder);
		}

		return txObject;
	}

1、创建HibernateTransactionObject对象

HibernateTransactionObject txObject = new HibernateTransactionObject();

HibernateTransactionObject 是一个Hibernate事务对象，代表一个SessionHolder。被HibernateTransactionManger用作事务对象。

2、进入SessionHolder

SessionHolder： session持有者，包装了一个Hibernate Session和一个Hibernate事务

三 、进入doGetTransaction的其中一个实现类JDBC中的DataSourceTransactionManager 类

进入doGetTransaction方法

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

1、创建DataSourceTransactionObject实例

DataSourceTransactionObject txObject = new DataSourceTransactionObject();进入DataSourceTransactionObject

DataSourceTransactionObject也是继承自JdbcTransactionObjectSupport

三、回到AbstractPlatformTransactionManager类的getTransaction方法进入如下代码

如果已经存在事务，则检查事务的传播行为

2、进入handleExistingTransaction方法

/**
	 * Create a TransactionStatus for an existing transaction.
	 */
	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 {
				boolean newSynchronization = (getTransactionSynchronization() != SYNCHRONIZATION_NEVER);
				DefaultTransactionStatus status = newTransactionStatus(
						definition, transaction, true, newSynchronization, debugEnabled, suspendedResources);
				doBegin(transaction, definition);
				prepareSynchronization(status, definition);
				return status;
			}
			catch (RuntimeException beginEx) {
				resumeAfterBeginException(transaction, suspendedResources, beginEx);
				throw beginEx;
			}
			catch (Error beginErr) {
				resumeAfterBeginException(transaction, suspendedResources, beginErr);
				throw beginErr;
			}
		}

		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);
	}

原文地址：https://www.cnblogs.com/linlf03/p/11221498.html