It really depends. I trained with their JSDF in 2012 and they're quite good, if something went down they'd fight to the last. That said, they're a small force and too focused on naval superiority even though they have some excellent terrain and regions that would be Nam 2.0 for any country if they focused their ground forces on asymmetrical and guerilla warfare, they could last at least a year, but the ground forces are primarily focused on blitz style, hit and pull back then hit again, regular warfare. Their air force should be superior to China's but that's a numbers game like their navy and you can't really hit and run then hide in the air or water.