I have defined (correctly) a user defined function that is referred to in a JRXML file. IT works fine when I first create it.
I also define some DSPs etc to fill the report. When I first create these, it is all fine.
I exit Jaspersoft Studio and then restart it and for some reason JasperSoft Studio does not recognize my Java classes. I get errors like "The method xXxxxx is indefined for the time XXXXx". If I try to run a subreport with a specific DSP then it reports ClassNotFoundException.
Magically if I go and play with the config files, I can trick Jaspersoft Studio into rebuilding the app and things start working again.
I have not figured out however which particular configuration file I need to touch to make this happen.