code: boolean serveStaticResource(HttpServletRequest req, StaplerResponse rsp, OpenConnection con, long expiration) throws IOException {
          if (con == null) return false;
          try {
              return serveStaticResource(req, rsp, con.stream,
                      con.getLastModified(),
                      expiration,
                      con.connection.getContentLength(),
                      con.connection.getURL().toString());
          } finally {
              con.close();
          }
      }
docs: Serves the specified {@link URLConnection} as a static resource.