Ja Rule Says Fat Joe 'In Good Spirits' Despite Underage Sex Lawsuit

Ja Rule says Fat Joe's "All the Way Up" amid his new legal headache ... telling us the rapper's in good spirits despite the claims of underage sex against him.

We caught up with Ja at Hot 97's Summer Jam concert in New Jersey Friday ... and, we had to ask him about how his friend and fellow New York-born rapper is doing after a man named Terrance Dixon filed a lawsuit against him this week.

ICYMI ... Dixon -- represented by attorney Tyrone A. Blackburn -- is suing Joe and alleging Joe had a sexual relationship with multiple underage girls. Fat Joe's attorney, Joe Tacopina, called the allegations "lies intended to damage his reputation and force a settlement through public pressure."

Ja says he actually spoke to Fat Joe just a before he performed a tribute to Irv Gotti at the festival -- and, he's doing well despite everything going on.

In fact, JR admits he checked in to see if Joe could perform with him ... but, the dude had his own show to do Friday and couldn't make it.

Ja's clearly got love for Fat Joe still ... and, he's not the only rapper offering him support during this trying time. 50 Cent posted earlier Saturday that claims about Joe trying to assassinate him -- also made in the lawsuit -- are total BS.

As we said ... Ja was at the event to pay tribute to Irv Gotti who passed away in February after persistent health issues - and, he opens up about the emotional toll Irv's death has taken on him.