code: static long getDateHeader(final String pHeaderValue) {
          long date = -1L;
          if (pHeaderValue != null) {
              date = HTTPUtil.parseHTTPDate(pHeaderValue);
          }
          return date;
      }
docs: Utility to read a date header from a cached response.
  
  @param pHeaderValue the header value
  @return the parsed date as a long, or {@code -1L} if not found
  @see javax.servlet.http.HttpServletRequest#getDateHeader(String)