ORA-06401: NETCMN: invalid driver
designator while using jdbc:oracle:oci8:@mytestdb:1521:DB1 in hibernate

"you should read the docus for the _oci_ jdbc url carefully: there is no
need for the 1521 port part, you have to put a TNS name of the oracle
service descriptor (have a look at listener.ora in network/admin on the
server and the tnsnames.ora on the client - but this depends on the oracle
naming service you are using) into it."