code: public static void addEntry(final File zip, final ZipEntrySource entry) {
      operateInPlace(zip, new InPlaceAction() {
        public boolean act(File tmpFile) {
          addEntry(zip, entry, tmpFile);
          return true;
        }
      });
    }
docs: Changes a zip file, adds one new entry in-place.
  
  @param zip
  an existing ZIP file (only read).
  @param entry
  new ZIP entry appended.