code: private static File toJar(final File file) throws IOException {
      final File tempFolder = Files.createTempDirectory("reef-tmp-tempFolder").toFile();
      final File jarFile = File.createTempFile(file.getCanonicalFile().getName(), ".jar", tempFolder);
      LOG.log(Level.FINEST, "Adding contents of folder {0} to {1}", new Object[]{file, jarFile});
      try (final JARFileMaker jarMaker = new JARFileMaker(jarFile)) {
        jarMaker.addChildren(file);
      }
      return jarFile;
    }
docs: Turns temporary folder "foo" into a jar file "foo.jar".
  
  @param file
  @return
  @throws IOException