Josh Brolin -- Checks Into Rehab After Swearing Off Booze

Josh Brolin is trying to live up to his promise ... he's reportedly checked into rehab after telling TMZ he was swearing off booze for good.

Brolin checked into a rehab facility recently in Northern California ... a source told Us Weekly he realized he needed help and is committed to his sobriety.

TMZ broke the stories ... Josh got into into a drunken barfight in Santa Monica earlier this month that was caught on video ... and that same weekend, he tangled with a cab driver after rear-ending the guy.