I have flown long haul JAL three times in the past year; twice in J, once in F.

The two times in J, I was in a window seat and the temperature was perfect, cold even. One was on the newer 787 and once on the 777.

The only time in F, my significant other and I were in the middle seats, and I definitely found it warm, though my SO did not. She prefers warmer temperatures however.