獲取客戶端的IP地址（過濾代理）

下面的工具， 能滿足絕大部分應用環境，但並不是百分百。

 //獲取ip
    public static String getIpAddress(HttpServletRequest request) {
        String ip = null;

        //X-Forwarded-For：Squid 服務代理
        String ipAddresses = request.getHeader("X-Forwarded-For");

        if (ipAddresses == null || ipAddresses.length() == 0 || "unknown".equalsIgnoreCase(ipAddresses)) {
            //Proxy-Client-IP：apache 服務代理
            ipAddresses = request.getHeader("Proxy-Client-IP");
        }

        if (ipAddresses == null || ipAddresses.length() == 0 || "unknown".equalsIgnoreCase(ipAddresses)) {
            //WL-Proxy-Client-IP：weblogic 服務代理
            ipAddresses = request.getHeader("WL-Proxy-Client-IP");
        }

        if (ipAddresses == null || ipAddresses.length() == 0 || "unknown".equalsIgnoreCase(ipAddresses)) {
            //HTTP_CLIENT_IP：有些代理服務器
            ipAddresses = request.getHeader("HTTP_CLIENT_IP");
        }

        if (ipAddresses == null || ipAddresses.length() == 0 || "unknown".equalsIgnoreCase(ipAddresses)) {
            //X-Real-IP：nginx服務代理
            ipAddresses = request.getHeader("X-Real-IP");
        }

        //有些網絡通過多層代理，那麼獲取到的ip就會有多個，一般都是通過逗號（,）分割開來，並且第一個ip爲客戶端的真實IP
        if (ipAddresses != null && ipAddresses.length() != 0) {
            ip = ipAddresses.split(",")[0];
        }

        //還是不能獲取到，最後再通過request.getRemoteAddr();獲取
        if (ip == null || ip.length() == 0 || "unknown".equalsIgnoreCase(ipAddresses)) {
            ip = request.getRemoteAddr();
        }
        return ip;
    }