Not sure if this an issue with B4J but very confusing nonetheless. I have used File.Copy() to selectively transfer a large number of .mp3 files to pre-created folders on my NAS.
However.... When I open the mobile streaming app that navigates to the NAS the folders are present but appear empty. Viewing the NAS via Windows Explorer shows all the files are present and correct. They are playable and have identical file attributes to the source files. If I copy some files to the NAS with Windows Explorer they appear in the streaming app immediately.
If I use Win Explorer to move the files copied with B4J to another folder on the NAS they also appear on the streaming app immediately. There seems to be something about the B4J File.Copy() process that is different to the copy process in Explorer.
The cause appears to lie with the indexing of files by the NAS. When addressed as a Windows storage device by either WE or jShell(cmd copy) the files appear on the NAS immediately. When using the File.Copy() command the files miraculously appear after a period of time, presumably when the indexing utilised by the remote app has taken place.