The Japan of today is different to the Japan of the 40s. One cannot hold any member of the Japanese public alive to today for the sins of those from the 30s and 40s. What is done is done. History is history. China has no more right to invade or attack Japanese territory than Japan had in 1937.
It is quite infantile to claim "They did it to us, now we will do it to them" if indeed that is what the Chinese powers that be are thinking. And it's a poor argument for outsiders to use to justify any actions the Chinese might bring upon Japan.
Personally I think this is all sabre rattling which will eventually quieten down.
Japan is allied to a lot of nations with whom China trades. Biggest of all being the US. I don't think China can afford to cause a war to erupt between themselves and Japan for that reason.