Hi Andrea - on IRC you were having some trouble with the java logging stuff (used by a couple of the libraries such as GeoTools).
Aside: I note that the trouble with JAI spitting out an error messages does not seem to be related to logging. Basically we can use the pure java JAI jars; or expect them to print a message when they fail to find their library on the library path.
Back to logging - apparently there is a -D command line setting that can be used:
We could that add that to our VM Args for uDig - perhaps asking it to pick up a java logging properties file in the uDig application directory?
Note this is a general solution for configuring java logging; for GeoTools you can actually configure it to use different logging engines (log4j, sl4j etc…) using some method on the GeoTools class.