Assert file had been created in Junit (Java 6)

I'd like to write an integration for a Java program that takes an input file from source directory, copies it to staging, writes the result of processing to output directory and then removes the temporary files from staging. It's easy enough to check the output is ok, but is there an easy way to check the staging area is being used correctly? 2 things come to mind: monitoring the folder for file system events (any nice wrappers for that?), or some advanced permissions game (to allow create but not delete). Any suggestions?

Thanks a lot!

N.B. Java 6 on Windows...