By default you will receive only the Non-Partisan ballot. If you wish to vote in the Democratic Primary, you will need to take your ballot and its envelope to your precinct (the location is printed on the back of your sample ballot), surrender the ballot and envelope, and request to vote Democratic at the precinct.
If you want to avoid this problem in future, the best thing you can do is just register as a Dem. The Republicans exclude independents from their primary anyhow -- the only parties that allow participation are the Dems and the "American Independent Party" (which sucks in a lot of people who think they're registering as "independents", and then find that since they're actually registered with a party, they can't vote in the Dem primary, which allows Dems and actual independents).
It's actually not too late to re-register Dem -- the deadline is 1/22 -- but in order to actually get the Dem ballot, if you already have an absentee ballot, you'd have to go do your re-registration at the Registrar's office (for Santa Clara County, that's in San Jose) and surrender your current ballot and envelope; then you can just fill out your ballot there before you leave. I'm not sure whether they'll let you take a new ballot home with you.
If you insist on remaining registered Non-Partisan, you can get the Dem ballot for future primaries by going to your County Registrar's site before each primary election, and finding the form equivalent to the ones listed here. Check out the form behind the "English" link and note the box on the right side for "Voters not affiliated with a qualified political party". I would recommend mailing this form in at least six weeks before the election; I believe it has to have been processed by 30 days before the election, because absentee ballots start getting mailed out 29 days before the election.