After 17 years in Sag Harbor, Java Nation, a coffee roaster whose owners take their beans very, very seriously, has moved to Bridgehampton, taking a space in a semi-industrial row of buildings near the train station. A small cafe in front expected to open by Memorial Day weekend will serve up hot cups of Joe, cappuccino, and espresso with a few baked goods and teas to round things out. The big deal here is beans, with devotees willing to drive miles to stock up. As of May 10, the roaster was up and running, with someone there 9 a.m. to 3 p.m., more or less.