如何从http请求获取子网ip地址

Question

I'm writing a web application, I need to do a audit log for all the actions in the application. For this purpose I need to get the IP Address of the client systems.

I'm using request.getRemoteAddr() to get the remote IP Address. But this has a problem, if the client is behind a proxy this method will give the IP of the proxy system.

When I did some search I found a header attribute called 'X-FORWARDED-FOR' in the HttpRequest object.

Can somebody tell me how exactly this header property works and how can I used this header to get the IP address of the client system.

Thank you

Answer 1

getRemoteIP returns the remote IP address of the user (assuming all HTTP intermediaries are well behaved wrt XFF header).

String getRemoteIP(HttpServletRequest request) {
    String xff = request.getHeader("X-Forwarded-For");
    if (xff != null) {
        return xff.split("[\\s,]+")[0];
    }
    return request.getRemoteAddr();
}

Answer 2

客户端的代理（通常是防火墙等）将使用从客户端接收到的ip填充x-forward-for标头，通常这是（但不是必须的）（在用户经过多个代理或防火墙）用户计算机的IP。

Answer 3

'X-FORWARDED-FOR' is used for identifying the originating/actual IP address of a client connecting to a web server through an HTTP proxy.

You can simply use the value for this attribute to find out the originating client IP, even if it's behind a proxy.