leExistingTransaction(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 {
/*
由于没有检测到事务，因此需要开启一个事务来支持事务的有关操作
*/
return startTransaction(def, transaction, debugEnabled, suspendedResources);
}
catch (RuntimeException | Error ex) {
resume(null, suspendedResources);
throw ex;
}
}
else {
boolean newSynchronization = (getTransactionSynchronization() == SYNCHRONIZATION_ALWAYS);
return prepareTransactionStatus(def, null, true, newSynchronization, debugEnabled, null);
}
}
继续分析获取事务的代码，可以看到实际上最终是通过 TransactionSynchronizationManager 来检查绑定的事务信息的
// 获取当前绑定的事务
protected Object doGetTransaction() {
DataSourceTransactionObject txObject = new DataSourceTransactionObject();
txObject.setSavepointAllowed(isNestedTransactionAllowed());
/*
获取与当前线程绑定的事务信息
*/
ConnectionHolder conHolder =
(ConnectionHolder) TransactionSynchronizationManager.getResource(obtainDataSource());
txObject.setConnectionHolder(conHolder, false);
return txObject;
}
/*
检查当前线程持有的事务是否是有效的，如果在 doGetTransaction 方法中 TransactionSynchronizationManager
中能够检测到对应的 ConnectionHolder 并且是活跃的，则说明确实在方法执行前就已经存了事务
*/
protected boolean isExistingTransaction(Object transaction) {
DataSourceTransactionObject txObject = (DataSourceTransactionObject) transaction;
return (txObject.hasConnectionHolder() && txObject.getConnectionHolder().isTransactionActive());
}
// JdbcTransactionObjectSupport
public boolean hasConnectionHolder() {
return (this.connectionHolder != null);
}
如果当前已经存在了事务，需要针对事务传播行为对当前的事务做出对应的行为：
private TransactionStatus handleExistingTransaction(
TransactionDefinition definition,
Object transaction,
boolean debugEnabled)
throws TransactionException {
/*
由于默认的是传播行为是 PROPAGATION_REQUIRED，即默认将当前的处理加入到当前已经存在的事务中，
我们主要关心这部分内容，因此省略了其它传播行为的处理
*/
boolean newSynchronization = (getTransactionSynchronization() != SYNCHRONIZATION_NEVER);
return prepareTransactionStatus(definition, transaction, false, newSynchronization, debugEnabled, null);
}
继续查看对于当前事务的处理：
// 简单地标记一下当前的事务状态
protected final DefaultTransactionStatus prepareTransactionStatus(
TransactionDefinition definition, @Nullable Object transaction, boolean newTransaction,
boolean newSynchronization, boolean debug, @Nullable Object suspendedResources) {
DefaultTransactionStatus sta