public Set<FileHandle> getOfflineFiles() throws FileNotFoundException {
		Set<FileHandle> allFiles = getFiles();
		Set<FileHandle> offlineFiles = new HashSet<FileHandle>(allFiles.size());
		
		for (FileHandle file : allFiles) {
			if (!file.isAvailable())
				offlineFiles.add(file);
		}
		
		return offlineFiles;
	}