This song is from the soundtrack of the Bradley Cooper and Jennifer Lawrence starring film Silver Linings Playbook. It was written by hit-maker Diane Warren.
The song was leaked on the net on October 29, 2012. "So… :) @Diane_Warren was asked to write the leading soundtrack song for a new movie called #SilverLining and so @Diane_Warren wrote #crazyboutyou," Jessie J tweeted about the leak. "Then.. @Diane_Warren asked me to sing It for the movie *happy dance* obvs I said yes."