As far as I know Temenos has provided the below utilities for jbase.
EB.FILE.STATS - contains file stats
JFSTAT - the program which does the analysing for file stats. Based on these files, you can write a routine to do resizing.
Just check the attached file to get more info.
However, if we just type jrf at the prompt it will start resizing all the files one by one. I think this is not a good approach.