How to Implement Global IP‑Based User Location Display in Java

Modern mobile apps and websites often display a user’s location without distinction. To achieve this based on the client’s IP address, a Java backend must first obtain the real IP from the incoming request.

Retrieving the Client IP

The following utility method extracts the IP address from an HttpServletRequest. It checks common proxy headers ( x-forwarded-for, Proxy-Client-IP, WL-Proxy-Client-IP, HTTP_CLIENT_IP, HTTP_X_FORWARDED_FOR) and falls back to request.getRemoteAddr(). If the address is a loopback ( 127.0.0.1 or 0:0:0:0:0:0:0:1), it resolves the actual host address via InetAddress.getLocalHost(). Finally, when the header contains multiple comma‑separated IPs, the method keeps only the first one.

public static String getIpAddr(HttpServletRequest request) {
    String ipAddress = request.getHeader("x-forwarded-for ");
    if (ipAddress == null || ipAddress.length() == 0 || "unknown ".equalsIgnoreCase(ipAddress)) {
        ipAddress = request.getHeader("Proxy-Client-IP ");
    }
    if (ipAddress == null || ipAddress.length() == 0 || "unknown ".equalsIgnoreCase(ipAddress)) {
        ipAddress = request.getHeader("WL-Proxy-Client-IP ");
    }
    if (ipAddress == null || ipAddress.length() == 0 || "unknown".equalsIgnoreCase(ipAddress)) {
        ipAddress = request.getHeader("HTTP_CLIENT_IP");
    }
    if (ipAddress == null || ipAddress.length() == 0 || "unknown".equalsIgnoreCase(ipAddress)) {
        ipAddress = request.getHeader("HTTP_X_FORWARDED_FOR");
    }
    if (ipAddress == null || ipAddress.length() == 0 || "unknown ".equalsIgnoreCase(ipAddress)) {
        ipAddress = request.getRemoteAddr();
        if(ipAddress.equals("127.0.0.1") || ipAddress.equals("0:0:0:0:0:0:0:1")){
            InetAddress inetAddress = null;
            try {
                inetAddress = InetAddress.getLocalHost();
            } catch (UnknownHostException e) {
                e.printStackTrace();
            }
            ipAddress = inetAddress.getHostAddress();
        }
    }
    if(null != ipAddress && ipAddress.length() > 15){
        // "***.***.***.***".length() = 15
        if(ipAddress.indexOf(",") > 0){
            ipAddress = ipAddress.substring(0, ipAddress.indexOf(","));
        }
    }
    return ipAddress;
}

Mapping IP to Geographic Region

Once the IP is obtained, the ip2region library can translate it into province and city information. The library works with a binary .xdb file and supports two lookup modes: a file‑based query that caches a VectorIndex, or a full in‑memory load of the .xdb for the fastest lookups.

<dependency>
    <groupId>org.lionsoul</groupId>
    <artifactId>ip2region</artifactId>
    <version>2.6.4</version>
</dependency>

The article notes that large providers already offer such services, but they often impose request limits. By integrating ip2region locally, developers avoid external rate limits while achieving reliable location resolution.

Conclusion

With the IP‑extraction utility and the ip2region dependency, a Java backend can reliably display a user’s geographic location across any web or mobile application.