String clientIp = request.getHeader("HTTP_X_FORWARDED_FOR");
if(null == clientIp || clientIp.lenght() == 0
   || clientIp.toLowerCase().equals("unknown")){
  clientIp = request.getHeader("REMOTE_ADDR");
}

if(null == clientIp || clientIp.lenght() == 0
   || clientIp.toLowerCase().equals("unknown")){
  clientIP = request.getRemoteAddr();
}