j2ee失去client的IP地址

	public static String getIp(HttpServletRequest req) {		try {			if (req == null) {				return null;			}			String ip_for = req.getHeader(" x-forwarded-for ");			String ip_client = req.getHeader(" http_client_ip ");			String un = " unknown ";			if (ip_for != null && !ip_for.equalsIgnoreCase(un)					&& ip_for.trim().length() > 0) {				return ip_for;			} else if (ip_client != null && !ip_client.equalsIgnoreCase(un)					&& ip_client.trim().length() > 0) {				return ip_client;			} else {				return req.getRemoteAddr();			}		} catch (Exception e) {			LOGGER.error("Error: get ip failure : " + e.getMessage());		}		return null;	}

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