code: private InputStream startExternal(String fileName) {
  		InputStream result = null;
  		try {
  			String extension = getExtension(fileName);
  			String command = externalSupport.get(extension).replace(
  					FILEPLACEHOLDER, fileName);
  			Process externalProcess = Runtime.getRuntime().exec(command);
  			result = externalProcess.getInputStream();
  		} catch (IOException ignore) {
  		}
  		return result;
  	}
docs: Start an external utility to unpack the the archive
  
  @param fileName
  @return InputStream to read the decompressed data