Justin Baldoni certainly doesn't look like a guy in the middle of a nasty legal battle with his "It Ends With Us" costar Blake Lively -- even though both have been at each other's throats.

Check out new photos, obtained by TMZ ... Justin -- who also directed the controversial film -- was photographed Saturday splashing around the waters on the sandy beaches of Maui, Hawaii.

Justin was also filmed with his shirt off -- putting his ripped abs on full display while flashing a big smile. Our sources say his kids and friends were having some fun in the sun, too.

Justin's carefree attitude flies in the face of his tense legal drama with Blake after the two clashed on the set of "It Ends With Us."

As you know, Blake first filed a California Civil Rights Department complaint against Justin, followed by a federal lawsuit accusing him of sexual harassment and trying to destroy her reputation after the movie was released.

Then Justin filed his own lawsuit against the New York Times for allegedly dragging his name through the mud in a bombshell article siding with Blake on all the back-stabbing behind the scenes.