@Override
  public Transaction getTransaction() throws SystemException {
    if (!isActive) {
      throw new SystemException(
          "TransactionManager invalid");
    }
    Thread thread = Thread.currentThread();
    Transaction txn = (Transaction) transactionMap.get(thread);
    return txn;
  }
Get the transaction associated with the calling thread

@see javax.transaction.TransactionManager#getTransaction()
geode-core/src/main/java/org/apache/geode/internal/jta/TransactionManagerImpl.java