It may be way easier to try to change DB settings (and possibly update): MAX_STRING_SIZE = EXTENDED will allow way more characters (32k). See https://docs.oracle.com/en/database/oracle/oracle-database/19/sqlrf/Data-Types.html#GUID-7B72E154-677A-4342-A1EA-C74C1EA928E6

If that is not an option, as pointed in another answer, Java uses UTF-16, you are storing UTF-8 it seems. Use some function to transfer between charsets (sorry, can't help on that part) and then partition. I would not go that low unless absolutely needed.