使用java获取客户端计算机的ip地址

Question

I am supposed to capture the ip address of the client machine , who hits my web application. After googling, I have found two ways :

1. request.getRemoteAddr()

2. request.getHeader("X-FORWARDED-FOR")

but both of them do not guarantee returning the actual ip of the client machine. Also, I am supposed to achieve the same using struts1.2 , as the application is developed in struts1.2.

Is there any struts class for the same?

I am using the following code:

String ipAddress = request.getHeader("X-FORWARDED-FOR");  
if (ipAddress == null) {  
    ipAddress = request.getRemoteAddr();  
}

but the method request.getHeader("X-FORWARDED-FOR"); returns null when I access the application from a mobile or wireless device.

As a result, ip is obtained from method request.getRemoteAddr(); The issue is the ip retrieved is private and not public but i want the public ip of client.

Answer 1

request.getRemoteAddr() will return the correct address in most cases (this is part of Java EE not struts). They do not guarantee returning the actual IP of the client machine as this is problem of the TCP/IP limitation, not structs or Java itself.

Answer 2

The problem is that there's just no way to guarantee it. The client might be NAT-ted, so you won't be able to find the address that the client knows in that case anyway, and if the client connects by a proxy (common for certain classes of device, or when the connection is from some locations) then there's no way to guarantee that the proxy will tell you what the client's address is. There are some horribly broken proxies out there, and even when working correctly they may still be configured to hide the information you are looking for.

The easiest technique might be to run some javascript on client to discover the information and send it to you in a background request. But then you'll discover that the client's address is often not very useful anyway. You surely can't use it for authentication purposes (the widespread prevalence of NAT and dynamic address allocation via DHCP means that you'll often get different clients with the same “internal” address) or connecting back to the client (most clients run a strong firewall or are behind one) and I have no idea why you'd even want to log it. It's about the most useless thing you could ask for. I advise taking a step back from this problem and to think again about what you're really trying to do.