This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
Moving to your question - Try inserting Japanese characters from backend into database and see if you are able to insert or still getting some error. If you get any error then post it over here and look for resolution.
If you are able to insert it from backend and it is creating issue while inserting Japanese characters from java then you may have to encode them. I also insert Chinese and Arabic characters into database from java, i will try to figure it out and will post over here.