code: public static String getIpAddr(HttpServletRequest request) {
      String ip = request.getHeader("x-forwarded-for");
      if (ip == null || ip.length() == 0 || "unknown".equalsIgnoreCase(ip)) {
        ip = request.getHeader("Proxy-Client-IP");
      }
      if (ip == null || ip.length() == 0 || "unknown".equalsIgnoreCase(ip)) {
        ip = request.getHeader("WL-Proxy-Client-IP");
      }
      if (ip == null || ip.length() == 0 || "unknown".equalsIgnoreCase(ip)) {
        ip = request.getRemoteAddr();
      }
      return ip;
    }
docs: Returns remote ip address.
  <ul>
  <li>First,it lookup request
  header("x-forwarded-for"->"Proxy-Client-IP"->"WL-Proxy-Client-IP")
  <li>Second,invoke request.getRemoteAddr()
  </ul>
  
  @param request