It has been a long time since I tried this as I am not a MySQL user by preference:
This should allow the use of unicode strings. Have you tried that?
I'm not sure whether the connection-property tags with the latest JBoss releases work. You can experiment.
Hope that might help.
i'll give it a try as soon as possible and report the results.
a little time has passed but my problem still exists :(
i have tried with the connection string properties as suggested by jonlee:
now the string are written apparently correct in the db but, when i read them back, i get a series of ??????? instead of greek characters.
I'm a little stuck :-\