China has a huge active army and the double in reserve, besides we never know what they are hiding. The Japanese airstrikes (tora tora style?) are useless vs a big country and their mainland isn't far from China to prevent the flooding troops.
China can arm 100 million of its 1,300 million citizens, and even that won't guarantee them victory in a war against Japan. I know the level of training these PLA cadre receive. It is very much rudimentary. On the other hand, the Japanese soldiers train with the Americans and the Europeans, and they receive the best training in the world. Chinese ballistic missiles and fighter jets will be shot down without much effort, while the Japanese ones will incinerate Beijing and Shanghai in a matter of seconds (Chinese air-defense is a joke).
War isn't only technology, it can be easily interrupted then...
Just to say it is a war between an army vs separatists (not 90% of random civilians and few separatists) 
. Back in 1894 during the first Sino-Japanese war the world thought the very same, but bureaucracy and corruption plagued the Chinese side so much what made the whole campaign a cakewalk for the numerically and technologically inferior but more organized and determined Japanese forces.
