How to Retrieve IP Geolocation in Java with ip2region – Step‑by‑Step Guide

Recently the platform added an IP location feature that shows the user's region when posting, commenting, or chatting. This tutorial demonstrates how to acquire the IP address in Java and convert it to geographic information.

Getting the IP Address

Use the

HttpServletRequest

(or

ServerHttpRequest

) to read the client IP from request headers. The typical headers are:

X-Forwarded-For : a chain of IPs added by proxies; the leftmost IP is the original client.

X-Real-IP : usually contains the real client IP.

Proxy-Client-IP : added by Apache when acting as a proxy.

WL-Proxy-Client-IP : added by WebLogic plugins.

The following utility class extracts the most reliable IP address:

<code>public class IpUtil {
    public static String getIpAddr(ServerHttpRequest request) {
        HttpHeaders headers = request.getHeaders();
        String ipAddress = headers.getFirst("X-Forwarded-For");
        if (ipAddress == null || ipAddress.length() == 0 || "unknown".equalsIgnoreCase(ipAddress)) {
            ipAddress = headers.getFirst("Proxy-Client-IP");
        }
        if (ipAddress == null || ipAddress.length() == 0 || "unknown".equalsIgnoreCase(ipAddress)) {
            ipAddress = headers.getFirst("WL-Proxy-Client-IP");
        }
        if (ipAddress == null || ipAddress.length() == 0 || "unknown".equalsIgnoreCase(ipAddress)) {
            ipAddress = request.getRemoteAddress().getAddress().getHostAddress();
            if (ipAddress.equals("127.0.0.1") || ipAddress.equals("0:0:0:0:0:0:0:1")) {
                try {
                    InetAddress inet = InetAddress.getLocalHost();
                    ipAddress = inet.getHostAddress();
                } catch (UnknownHostException e) {
                    log.error("Failed to get local IP", e);
                }
            }
        }
        if (ipAddress != null && ipAddress.indexOf(",") > 0) {
            ipAddress = ipAddress.split(",")[0];
        }
        return ipAddress;
    }
}
</code>

Choosing an IP Geolocation Library

The original Taobao IP service is no longer available, so the tutorial switches to ip2region , an offline database with 99.9% accuracy, millisecond‑level query speed, and a size of only a few megabytes. It supports many languages (Java, PHP, C, Python, Node.js, Go, C#) and offers three built‑in query algorithms.

ip2region Data and Algorithms

Data format:

_cityId|country|region|province|city|ISP_

. For Chinese IPs the city field is filled; for other countries only the country may be present.

Memory : loads the whole database into memory; fastest (≈0.1 ms per query).

Binary : binary search on the file; no memory load required (≈0.x ms).

B‑tree : B‑tree search on the file; slightly faster than binary (≈0.x ms).

Integrating ip2region

Add the Maven dependency:

<code>&lt;dependency&gt;
    &lt;groupId&gt;org.lionsoul&lt;/groupId&gt;
    &lt;artifactId&gt;ip2region&lt;/artifactId&gt;
    &lt;version&gt;1.7.2&lt;/version&gt;
&lt;/dependency&gt;
</code>

Place the

ip2region.db

file in the

resources

directory and load it in a utility class:

<code>static {
    dbPath = createFtlFileByFtlArray() + "ip2region.db";
    try {
        config = new DbConfig();
        searcher = new DbSearcher(config, dbPath);
    } catch (Exception e) {
        e.printStackTrace();
    }
}
</code>

Query the database using the chosen algorithm (B‑tree shown here):

<code>public static String getCityInfo(String ip) {
    if (StringUtils.isEmpty(dbPath)) {
        log.error("Invalid ip2region.db file");
        return null;
    }
    if (config == null || searcher == null) {
        log.error("DbSearcher or DbConfig is null");
        return null;
    }
    int algorithm = DbSearcher.BTREE_ALGORITHM;
    try {
        Method method = null;
        switch (algorithm) {
            case DbSearcher.BTREE_ALGORITHM:
                method = searcher.getClass().getMethod("btreeSearch", String.class);
                break;
            case DbSearcher.BINARY_ALGORITHM:
                method = searcher.getClass().getMethod("binarySearch", String.class);
                break;
            case DbSearcher.MEMORY_ALGORITYM:
                method = searcher.getClass().getMethod("memorySearch", String.class);
                break;
        }
        DataBlock dataBlock = (DataBlock) method.invoke(searcher, ip);
        String ipInfo = dataBlock.getRegion();
        if (!StringUtils.isEmpty(ipInfo)) {
            ipInfo = ipInfo.replace("|0", "").replace("0|", "");
        }
        return ipInfo;
    } catch (Exception e) {
        e.printStackTrace();
    }
    return null;
}
</code>

Wrap the result to return a user‑friendly location (province for China, country otherwise):

<code>/**
 * Get IP location
 */
public static String getIpPossession(String ip) {
    String cityInfo = getCityInfo(ip);
    if (!StringUtils.isEmpty(cityInfo)) {
        cityInfo = cityInfo.replace("|", " ");
        String[] cityList = cityInfo.split(" ");
        if (cityList.length > 0) {
            if ("中国".equals(cityList[0])) {
                if (cityList.length > 1) {
                    return cityList[1];
                }
            }
            return cityList[0];
        }
    }
    return "未知";
}
</code>

Running the

main

method shows the correct province or country for the given IP address.

Project Link

GitHub repository: https://github.com/lionsoul2014/ip2region