java programming/checksum implementation

i am working on an xml based content delivery/batch uploading project for a music aggregator using altova mapforce.i am maping metadata from a csv template of music releases to client specific xml templates and need to implement a checksum that checks the integrity and size of the audio and graphics files in each seperate project folder and sends the checksum data to the final xml file, in altova mapforce i can import user defined fucnctions and need someone who can program this and help make sure it works