Oracle equivalent of java currentTimeMillis

Instead of the
queryString = "SELECT systimestamp param FROM DUAL";

use the following
select extract(day from(systimestamp - to_timestamp('1970-01-01', 'YYYY-MM-DD'))) * 86400000 + to_number(to_char(sys_extract_utc(systimestamp), 'SSSSSFF3')) current_time_milliseconds
from dual;