Late Monday night, in the visitors' locker room at AT&T Center, Matt Barnes' iPhone lit up with a text from former Warriors teammate Stephen Jackson: Congrats, man! … In that moment Monday, after seeing Barnes help Golden State cap its four-game sweep of the Spurs in the Western Conference finals, Jackson recognized that this was about more than Barnes reaching his first NBA Finals. [...] as he tries to find a rhythm after missing four weeks with a sprained right ankle, he has no qualms about his sporadic playing time. Oakland is where he established himself as an NBA player, made some of his most lasting friendships and carved out a place in postseason lore. In the summer of 2006, after an underwhelming stint with Philadelphia left him with no more offers from NBA teams, Barnes — a former All-America wide receiver at Del Campo High School in Sacramento County — considered trying out for the NFL. [...] his old UCLA teammate, Baron Davis, invited him to a pickup game at Golden State's practice facility. Warriors head coach Don Nelson was impressed enough to invite Barnes to training camp. A former elementary schoolteacher who worked with special-needs students,...