如何确定HTTP和HTTPS请求中客户端的公共IP？

Question

I have read various blogs and done practically but couldn't get conclusive and full proof way to determine the get client public ip in all possible scenarios. The configuration on server side is: | F5 <--> Apache web server <--> Tomcat |

In code i first fetch and parse the request header X-FORWARDED-FOR to get the left most public ip. If not found i rely on request.getRemoteAddr() .

So question is:

1. This works well in some cases but fails when protocol is HTTPS. What can be done in this case?

2. If the X-Forwarded-For doesn't have any value then i have to rely on request.getRemoteAddr() which always give my server ip. This is because of apache web server which sits in between and getRemoteAddr returns the address of the client or last proxy that sent the request. How to overcome this scenario?

3. Is there any other headers on which i should read values apart from X-forwarded-for ?

4. What all are the other possible cases which should be handled?

Answer 1

String forwardedHeader  = servletRequest.getHeader("X-Forwarded-For");
clientIP =  servletRequest.getRemoteAddr();    

String forwarded = "";
if (forwardedHeader != null && !forwardedHeader.isEmpty())
{
    forwarded = forwardedHeader;

    int commaIdx = forwarded.indexOf(',');
    if (commaIdx > 0)
    {
        clientIP = forwarded.substring(0, commaIdx);
    }

    forwarded = forwarded.replace(',', '|');
}

if (forwarded != null && !forwarded.isEmpty())
{
    clientIP = forwarded;
}