code: protected Archive openArchive(File zipFilename) throws IOException {
          try {
              return openArchive(zipFilename, contextUseOptimizedZip);
          } catch (IOException ioe) {
              if (ioe instanceof ZipFileIndex.ZipFormatException) {
                  return openArchive(zipFilename, false);
              } else {
                  throw ioe;
              }
          }
      }
docs: /*
  This method looks for a ZipFormatException and takes appropriate
  evasive action. If there is a failure in the fast mode then we
  fail over to the platform zip, and allow it to deal with a potentially
  non compliant zip file.