You are wrong about the way Oracle stores dates, and are confusing how the date is stored and how it is presented to you. In DB2 you can specify the way it is presented to you with the CHAR function.
db2 select birthdate, char(birthdate, ISO), char(birthdate, usa) from db2inst1.employee
BIRTHDATE 2 3
---------- ---------- ----------
08/24/1963 1963-08-24 08/24/1963
02/02/1978 1978-02-02 02/02/1978
05/11/1971 1971-05-11 05/11/1971
09/15/1955 1955-09-15 09/15/1955
07/07/1975 1975-07-07 07/07/1975
05/26/2003 2003-05-26 05/26/2003
05/15/1971 1971-05-15 05/15/1971
12/18/1980 1980-12-18 12/18/1980
11/05/1959 1959-11-05 11/05/1959
In the first column it comes back in the command line processor as USA format because my DB2 Type 2 Windows client was installed with US territory code. Using the Type 4 universal client with java may have returned the ISO format, but you can probably specify which is the default to use with some Db2 connection parm or other DB2 setting once you connect (if you don't want to use the CHAR function).