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Java Offline GeoIP maps any IP address to its country code

There is a newer version: 0.1.12

package com.github.tornaia.geoip.internal;

import java.net.InetAddress;
import java.net.UnknownHostException;
import java.util.Arrays;

public class IpAddressMatcher {

    private final int nMaskBits;
    private final InetAddress requiredAddress;

    /**
     * Takes a specific IP address or a range specified using the IP/Netmask (e.g.
     * 192.168.1.0/24 or 202.24.0.0/14).
     *
     * @param ipAddress the address or range of addresses from which the request must
     *                  come.
     */
    public IpAddressMatcher(String ipAddress) {
        if (ipAddress.contains("/")) {
            String[] addressAndMask = ipAddress.split("/");
            ipAddress = addressAndMask[0];
            nMaskBits = Integer.parseInt(addressAndMask[1]);
        } else {
            nMaskBits = -1;
        }
        requiredAddress = parseAddress(ipAddress);
    }

    public boolean matches(String address) {
        InetAddress remoteAddress = parseAddress(address);

        if (!requiredAddress.getClass().equals(remoteAddress.getClass())) {
            return false;
        }

        if (nMaskBits < 0) {
            return remoteAddress.equals(requiredAddress);
        }

        byte[] remAddr = remoteAddress.getAddress();
        byte[] reqAddr = requiredAddress.getAddress();

        int oddBits = nMaskBits % 8;
        int nMaskBytes = nMaskBits / 8 + (oddBits == 0 ? 0 : 1);
        byte[] mask = new byte[nMaskBytes];

        Arrays.fill(mask, 0, oddBits == 0 ? mask.length : mask.length - 1, (byte) 0xFF);

        if (oddBits != 0) {
            int finalByte = (1 << oddBits) - 1;
            finalByte <<= 8 - oddBits;
            mask[mask.length - 1] = (byte) finalByte;
        }

        for (int i = 0; i < mask.length; i++) {
            if ((remAddr[i] & mask[i]) != (reqAddr[i] & mask[i])) {
                return false;
            }
        }

        return true;
    }

    private InetAddress parseAddress(String address) {
        try {
            return InetAddress.getByName(address);
        } catch (UnknownHostException e) {
            throw new IllegalArgumentException("Failed to parse address: " + address, e);
        }
    }
}