I took two readings of The Catcher in the Rye to understand the whole point of it. At first, I thought all that went on was Holden saying "sonuvabitch" and whining about phonies. Only upon reading it again that I learned that it was a tale of Holden stuck between childhood and adulthood. —Ray Ayanami
Another popular theme is that Holden suffers from PTSD from his brother's death, and the end is him finally realizing he needs help
In the beginning of the book, Holden says that he is a liar and he frequently lies to people who hold authority over him, in the ending of the book, Holden reveals that he is in a mental institution and is revealing his story in a position of authority, with this in mind, how much of the story can be interpreted as the truth of what happened to Holden?
Salinger refused to let the book be turned into a movie. Holden himself said he hates the movies, and he likely wouldn't want some "phony actor" pretending to be him.