how to autogen a primary key instead of passing it in?

[Patrick]

I have a Java service that creates a Facility.  Right now I specify
the primary key (facilityId) manually.  I would like the database to
automatically provide me with next available integer to use as the
primary key.   How can I accomplish this in my java service?

UtilMisc.toMap( "facilityId", (Object)facilityId);  //right now I am
passing in the pk but I want an automatically gen'd pk

Thank you very much in advance,
Patrick