How can I retrieve IP address from HTTP header in Java [duplicate]

Even though there's an accepted answer that has been highly upvoted I'd like to suggest an alternative and point out shortcomings of the accepted answer.

request.getHeader("Remote_Addr") is specified to return exactly the same as request.getRemoteAddr(). Hence, it makes no sense to check both. Also note that getRemoteAddr is a method of javax.servlet.ServletRequest (i.e. HTTP-agnostic) while getHeader is in javax.servlet.http.HttpServletRequest.

Furthermore, some proxies use Client-IP rather than X-Forwarded-For. For a discussion see https://stackoverflow.com/a/7446010/131929.

I don't know how reliable the use of HTTP_X_FORWARDED_FOR over X-Forwarded-For is. In Java I'd rather use the direct, short form. For a discussion see https://stackoverflow.com/a/3834169/131929. Upper/lower case makes no difference because getHeader is specified to be case insensitive.

Java alternative

public final class ClientIpAddress {

  // CHECKSTYLE:OFF
  // https://stackoverflow.com/a/11327345/131929
  private static Pattern PRIVATE_ADDRESS_PATTERN = Pattern.compile(
      "(^127\\.)|(^192\\.168\\.)|(^10\\.)|(^172\\.1[6-9]\\.)|(^172\\.2[0-9]\\.)|(^172\\.3[0-1]\\.)|(^::1$)|(^[fF][cCdD])",
      Pattern.CANON_EQ);
  // CHECKSTYLE:ON

  private ClientIpAddress() {
  }

  /**
   * Extracts the "real" client IP address from the request. It analyzes request headers
   * {@code REMOTE_ADDR}, {@code X-Forwarded-For} as well as {@code Client-IP}. Optionally
   * private/local addresses can be filtered in which case an empty string is returned.
   *
   * @param request HTTP request
   * @param filterPrivateAddresses true if private/local addresses (see
   * https://en.wikipedia.org/wiki/Private_network#Private_IPv4_address_spaces and
   * https://en.wikipedia.org/wiki/Unique_local_address) should be filtered i.e. omitted
   * @return IP address or empty string
   */
  public static String getFrom(HttpServletRequest request, boolean filterPrivateAddresses) {
    String ip = request.getRemoteAddr();

    String headerClientIp = request.getHeader("Client-IP");
    String headerXForwardedFor = request.getHeader("X-Forwarded-For");
    if (StringUtils.isEmpty(ip) && StringUtils.isNotEmpty(headerClientIp)) {
      ip = headerClientIp;
    } else if (StringUtils.isNotEmpty(headerXForwardedFor)) {
      ip = headerXForwardedFor;
    }
    if (filterPrivateAddresses && isPrivateOrLocalAddress(ip)) {
      return StringUtils.EMPTY;
    } else {
      return ip;
    }
  }

  private static boolean isPrivateOrLocalAddress(String address) {
    Matcher regexMatcher = PRIVATE_ADDRESS_PATTERN.matcher(address);
    return regexMatcher.matches();
  }
}

PHP alternative

function getIp()
{
    $ip = $_SERVER['REMOTE_ADDR'];

    if (empty($ip) && !empty($_SERVER['HTTP_CLIENT_IP'])) {
        $ip = $_SERVER['HTTP_CLIENT_IP'];
    } elseif (!empty($_SERVER['HTTP_X_FORWARDED_FOR'])) {
        // omit private IP addresses which a proxy forwarded
        $tmpIp = $_SERVER['HTTP_X_FORWARDED_FOR'];
        $tmpIp = filter_var(
            $tmpIp,
            FILTER_VALIDATE_IP,
            FILTER_FLAG_IPV4 | FILTER_FLAG_NO_PRIV_RANGE | FILTER_FLAG_NO_RES_RANGE
        );
        if ($tmpIp != false) {
            $ip = $tmpIp;
        }
    }
    return $ip;
}