code: protected Object readJson(final InputStream is,
                              final Class cl,
                              final HttpServletResponse resp) throws ServletException {
      if (is == null) {
        return null;
      }
  
      try {
        return getMapper().readValue(is, cl);
      } catch (Throwable t) {
        resp.setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
        if (debug()) {
          error(t);
        }
        throw new ServletException(t);
      }
    }
docs: Parse the request body, and return the object.
  
  @param is         Input stream for content
  @param cl         The class we expect
  @param resp       for status
  @return Object    Parsed body or null for no body
  @exception ServletException Some error occurred.