根据Request获取客户端IP

转自：

http://www.cnblogs.com/icerainsoft/p/3584532.html

http://www.cnblogs.com/bingya/articles/3134227.html

在JSP里，获取客户端的IP地址的方法是：request.getRemoteAddr() ，这种方法在大部分情况下都是有效的。但是在通过了Apache,Squid等反向代理软件就不能获取到客户端的真实IP地址了。
如
果使用了反向代理软件，将http://192.168.1.110:2046/ 的URL反向代理为http://www.xxx.com/
的URL时，用request.getRemoteAddr() 方法获取的IP地址是：127.0.0.1　或　192.168.1.110
，而并不是客户端的真实ＩＰ。
经过代理以后，由于在客户端和服务之间增加了中间层，因此服务器无法直接拿到客户端的IP，服务器端应用也无法直接
通过转发请求的地址返回给客户端。但是在转发请求的HTTP头信息中，增加了X－FORWARDED－FOR信息。用以跟踪原有的客户端IP地址和原来客
户端请求的服务器地址。当我们访问http://www.xxx.com/index.jsp/
时，其实并不是我们浏览器真正访问到了服务器上的index.jsp文件，而是先由代理服务器去访问http://192.168.1.110:2046
/index.jsp
，代理服务器再将访问到的结果返回给我们的浏览器，因为是代理服务器去访问index.jsp的，所以index.jsp中通过
request.getRemoteAddr() 的方法获取的IP实际上是代理服务器的地址，并不是客户端的IP地址。
于是可得出获得客户端真实IP地址的方法一：

 public String getRemortIP(HttpServletRequest request) {
   if (request.getHeader("x-forwarded-for") == null) {
    return request.getRemoteAddr();
   }
   return request.getHeader("x-forwarded-for");
 }

可是当我访问http://www.xxx.com/index.jsp/ 时，返回的IP地址始终是unknown，也并不是如上所示的127.0.0.1　或　192.168.1.110 了，而我访问http://192.168.1.110:2046/index.jsp 时，则能返回客户端的真实IP地址，写了个方法去验证。原因出在了Squid上。squid.conf 的配制文件　forwarded_for 项默认是为on，如果 forwarded_for 设成了 off 　则：X-Forwarded-For: unknown
于是可得出获得客户端真实IP地址的方法二：

 public String getRemoteHost(javax.servlet.http.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.getRemoteAddr();
     }
     return ip.equals("0:0:0:0:0:0:0:1")?"127.0.0.1":ip;
 }

如果是Netty4.x

 public String getRemoteIP(FullHttpRequest httpRequest) {
         String ip = "";
         try{
             String ipForwarded = httpRequest.headers().get("x-forwarded-for");
             if (StringUtils.isBlank(ipForwarded) || "unknown".equalsIgnoreCase(ipForwarded)) {
                 InetSocketAddress insocket = (InetSocketAddress)channel.remoteAddress();
                 ip = insocket.getAddress().getHostAddress();
             } else {
                 ip = ipForwarded;
             }
         }catch(Exception e){
             logger.error("getRemoteIP(): get remote ip fail!", e);
         }
         if("0:0:0:0:0:0:0:1".equals(ip)){
             ip = "127.0.0.1";
         }
         return ip;
     }

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

package com.ctrip.cep.mockserver.util;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import javax.servlet.http.HttpServletRequest;
import java.io.IOException;

/**
 * Created by lzyan on 2017/7/11.
 */
public final class NetworkUtil {
    private static Logger logger = LoggerFactory.getLogger(NetworkUtil.class);

    /**
     * 获取请求主机IP地址,如果通过代理进来，则透过防火墙获取真实IP地址
     *
     * @param request
     * @return
     * @throws IOException
     */
    public final static String getIpAddress(HttpServletRequest request) {
        // 获取请求主机IP地址,如果通过代理进来，则透过防火墙获取真实IP地址

        String ip = request.getHeader("X-Forwarded-For");
//        logger.debug("getIpAddress(HttpServletRequest) - X-Forwarded-For - String ip=" + ip);

        if (ip == null || ip.length() == 0 || "unknown".equalsIgnoreCase(ip)) {
            if (ip == null || ip.length() == 0 || "unknown".equalsIgnoreCase(ip)) {
                ip = request.getHeader("Proxy-Client-IP");
//                logger.debug("getIpAddress(HttpServletRequest) - Proxy-Client-IP - String ip=" + ip);
            }
            if (ip == null || ip.length() == 0 || "unknown".equalsIgnoreCase(ip)) {
                ip = request.getHeader("WL-Proxy-Client-IP");
//                logger.debug("getIpAddress(HttpServletRequest) - WL-Proxy-Client-IP - String ip=" + ip);
            }
            if (ip == null || ip.length() == 0 || "unknown".equalsIgnoreCase(ip)) {
                ip = request.getHeader("HTTP_CLIENT_IP");
//                logger.debug("getIpAddress(HttpServletRequest) - HTTP_CLIENT_IP - String ip=" + ip);
            }
            if (ip == null || ip.length() == 0 || "unknown".equalsIgnoreCase(ip)) {
                ip = request.getHeader("HTTP_X_FORWARDED_FOR");
//                logger.debug("getIpAddress(HttpServletRequest) - HTTP_X_FORWARDED_FOR - String ip=" + ip);
            }
            if (ip == null || ip.length() == 0 || "unknown".equalsIgnoreCase(ip)) {
                ip = request.getRemoteAddr();
//                logger.debug("getIpAddress(HttpServletRequest) - getRemoteAddr - String ip=" + ip);
            }
        } else if (ip.length() > 15) {
            String[] ips = ip.split(",");
            for (int index = 0; index < ips.length; index++) {
                String strIp = ips[index];
                if (!("unknown".equalsIgnoreCase(strIp))) {
                    ip = strIp;
                    break;
                }
            }
        }
        return ip;
    }

}