Check if the given transaction object indicates an existing transaction (that is, a transaction which has already started).
True if there is an existing transaction.
The result will be evaluated according to the specified propagation behavior for the new transaction. An existing transaction might get suspended (in case of PROPAGATION_REQUIRES_NEW), or the new transaction might participate in the existing one (in case of PROPAGATION_REQUIRED). Default implementation returns false, assuming that detection of or participating in existing transactions is generally not supported. Subclasses are of course encouraged to provide such support.
|TransactionException||In the case of system errors.|