在Servlet中获取真实的客户端IP

我在一个简单的问题上遇到了一些麻烦。我想要在一个HTTPServlet中获取真实的客户端IP。之前我使用的是：

request.getRemoteAddr()

但现在它返回了一个错误的IP。例如：xxx.xxx.xxx.50，但我的IP应该是xxx.xxx.xxx.159。（在http://whatismyipaddress.com/上进行了检查）。现在我尝试使用：

request.getHeader("X-Forwarded-For")

它返回NULL。我还使用了以下类进行了探测：

public class IpUtils {
public static final String _255 = "(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)";
public static final Pattern pattern = Pattern.compile("^(?:" + _255 + "\\.){3}" + _255 + "$");
public static String longToIpV4(long longIp) {
    int octet3 = (int) ((longIp >> 24) % 256);
    int octet2 = (int) ((longIp >> 16) % 256);
    int octet1 = (int) ((longIp >> 8) % 256);
    int octet0 = (int) ((longIp) % 256);
    return octet3 + "." + octet2 + "." + octet1 + "." + octet0;
}
public static long ipV4ToLong(String ip) {
    String[] octets = ip.split("\\.");
    return (Long.parseLong(octets[0]) << 24) + (Integer.parseInt(octets[1]) << 16)
            + (Integer.parseInt(octets[2]) << 8) + Integer.parseInt(octets[3]);
}
public static boolean isIPv4Private(String ip) {
    long longIp = ipV4ToLong(ip);
    return (longIp >= ipV4ToLong("10.0.0.0") && longIp <= ipV4ToLong("10.255.255.255"))
            || (longIp >= ipV4ToLong("172.16.0.0") && longIp <= ipV4ToLong("172.31.255.255"))
            || longIp >= ipV4ToLong("192.168.0.0") && longIp <= ipV4ToLong("192.168.255.255");
}
public static boolean isIPv4Valid(String ip) {
    return pattern.matcher(ip).matches();
}
public static String getIpFromRequest(HttpServletRequest request) {
    String ip;
    boolean found = false;
    if ((ip = request.getHeader("x-forwarded-for")) != null) {
        StringTokenizer tokenizer = new StringTokenizer(ip, ",");
        while (tokenizer.hasMoreTokens()) {
            ip = tokenizer.nextToken().trim();
            if (isIPv4Valid(ip) && !isIPv4Private(ip)) {
                found = true;
                break;
            }
        }
    }
    if (!found) {
        ip = request.getRemoteAddr();
    }
    return ip;
}
}

它也返回了xxx.xxx.xxx.50的IP。:( 现在我不知道如何获取真实的客户端IP。如果有人知道解决方案，请给出答案。