Use Java to Get Client's IP Address

This post is transferred from my old Hexo blog site, created on 2014.

I found a very useful StackOverflow post, which is about getting client's ip address using java. Note: JavaScript itself is unable to do this. However, there are seveal website providng API that you can make ajax call to it.

From basZero, a complate way is:

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.getHeader("HTTP_X_FORWARDED_FOR");
}
if (ip == null || ip.length() == 0 || "unknown".equalsIgnoreCase(ip)) {
    ip = request.getHeader("HTTP_X_FORWARDED");
}
if (ip == null || ip.length() == 0 || "unknown".equalsIgnoreCase(ip)) {
    ip = request.getHeader("HTTP_X_CLUSTER_CLIENT_IP");
}
if (ip == null || ip.length() == 0 || "unknown".equalsIgnoreCase(ip)) {
    ip = request.getHeader("HTTP_CLIENT_IP");
}
if (ip == null || ip.length() == 0 || "unknown".equalsIgnoreCase(ip)) {
    ip = request.getHeader("HTTP_FORWARDED_FOR");
}
if (ip == null || ip.length() == 0 || "unknown".equalsIgnoreCase(ip)) {
    ip = request.getHeader("HTTP_FORWARDED");
}
if (ip == null || ip.length() == 0 || "unknown".equalsIgnoreCase(ip)) {
    ip = request.getHeader("HTTP_VIA");
}
if (ip == null || ip.length() == 0 || "unknown".equalsIgnoreCase(ip)) {
    ip = request.getHeader("REMOTE_ADDR");
}
if (ip == null || ip.length() == 0 || "unknown".equalsIgnoreCase(ip)) {
    ip = request.getRemoteAddr();
}
return ip;

When I test it, I found everything returns 'null' except the last one, request.getRemoteAddr(), gave the right IP address.