Here's a guy who's THRILLED to get out of 2019!!!

Boxing superstar Anthony Joshua rang in the new year on a beach in Barbados -- flexing and smiling ... and honestly, we can't really blame him!

Joshua had his worst moment as a pro fighter in 2019 -- when he got the snot beat out of him by Andy Ruiz back in June. It was AJ's first loss ... and it was really bad.

But, Joshua basically locked himself in the gym after that -- and redeemed himself in December ... outboxing Ruiz in the rematch to win back all 4 of his heavyweight belts.

Now, he's back on top and on track to fight either Deontay Wilder or Tyson Fury in what could be one of the biggest fights EVER.

He's also agreed to be Fury's sparring partner to help Tyson train up for his Feb. 22 rematch against Wilder. No word on when Joshua will head to Detroit for that work.