javaweb获取用户真实ip

获取用户真实IP地址，不使用request.getRemoteAddr();的原因是有可能用户使用了代理软件方式避免真实IP地址, 
可是，如果通过了多级反向代理的话，X-Forwarded-For的值并不止一个，而是一串IP值，究竟哪个才是真正的用户端的真实IP呢？ 
答案是取X-Forwarded-For中第一个非unknown的有效IP字符串。 
如：X-Forwarded-For：192.168.1.110, 192.168.1.120, 192.168.1.130, 192.168.1.100 

用户真实IP为： 192.168.1.110 

public static String getIpAddress(HttpServletRequest request) {       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();       }       return ip;     }