java得到客户端IP问题

目前我得到客户端的IP方法是这么定义的，但100个IP记录中，还有那么几个IP获取不了。想了半天没找到具体原因，各大帮忙想想？
public static String getIpAddr(HttpServletRequest request) throws UnknownHostException {
        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.getHeader("HTTP_CLIENT_IP");
        }
        if (ip == null || ip.length() == 0 || "unknown".equalsIgnoreCase(ip)) {
            ip = request.getHeader("HTTP_X_FORWARDED_FOR");
        }
        if (ip == null || ip.length() == 0 || "unknown".equalsIgnoreCase(ip)) {
            ip = request.getRemoteAddr();
        }
        if(ip != null && ip.equalsIgnoreCase("0:0:0:0:0:0:0:1"))  
        {
          ip =InetAddress.getLocalHost().getHostAddress().toString();
        }
        return ip;
    }