code: public static final TxnId decode(final UUID txnId) {
          Preconditions.checkNotNull(txnId, "txnId");
          return TxnId.newBuilder()
                  .setHighBits(txnId.getMostSignificantBits())
                  .setLowBits(txnId.getLeastSignificantBits())
                  .build();
      }
docs: Returns TxnId object instance for a given transaction with UUID.
  
  @param txnId UUID
  @return Instance of TxnId.