Take a look at the java.io.File class and the various InputStream/OutputStream and Reader/Writer classes provided in the java.io package also. The File class can be used on files or directories... File.list() returns an array of filenames if the File object is a directory. You would then open a FileInputStream or a FileReader, depending on whether you wanted to read binary or character information from the file.
Even though you may be doing this over RMI, this question involves just plain old Java file io, so I'll move this to the "I/O and Streams" forum.
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