*/
private File[] getChunkFilenames(String fileName, char sep) throws Exception {
// scan for all chunks:
String prefix = fileName + sep;
String expression = prefix + '*';
File[] files = this.tmpDirectory.listFiles(new FilenameFilter(expression, false));
if (files.length > 0) {
TreeMap map = new TreeMap();
for (int i=0; i < files.length; i++) {
long postfix = extractNumberPostfixFromFile(files[i].getName(), prefix);