reverse ip2country

ReverseIP2Country.java

import com.maxmind.geoip2.DatabaseReader;
import com.maxmind.geoip2.exception.GeoIp2Exception;

import java.io.File;
import java.io.IOException;
import java.net.InetAddress;
import java.nio.file.Files;
import java.nio.file.Paths;

import static java.nio.file.StandardOpenOption.*;

/**
 * Reverse ip2country generator
 * Iterating trough range of IP addresses, appending each ip to a file named by its country.
 * 
 * TODO #1 
 * Optimization tip; if range of ips related to one country, which it mostly does,
 * for example 200.58.0.0 .. 200.71.125.255 are US
 * I should append to file the ip with wildcard on the subnet and not the whole range.
 * Currently it's overkill and not in scope.
 * 
 * Using Java 8 and com.maxmind.geoip2.geoip2 v2.10.0
 * @author Iddo Eldor
 */
public class ReverseIP2Country {

    private static final String DATABASE_FILE_LOCATION = "~/GeoIP2-City.mmdb";
    private static final String DATA_FOLDER = "~/data/"; // files will be created in this folder (add write premission)
    private static DatabaseReader databaseReader; // database interface

    private static IPAddress fromIp = new IPAddress("200.57.200.1"); // will iterate with this object
    private static final IPAddress TO_IP = new IPAddress("212.57.218.255"); // constant

    public static void main(String args[]) 
        throws IOException /* if file not found or cannot open */ 
    {
        databaseReader = new DatabaseReader.Builder(new File(DATABASE_FILE_LOCATION)).build();
        // iterate over the range of IPs
        do {
            fromIp = fromIp.next();
            String ip = fromIp.toString();
            String country = getCountryNameByIP(ip);
            // append ip to file named as country at /data, create file if not exist
            Files.write(Paths.get(DATA_FOLDER + country), (ip + System.lineSeparator()).getBytes(), CREATE, APPEND);
            System.out.println(ip);
        } while (!fromIp.equals(TO_IP));

    }

    private static /*synchronized*/ String getCountryNameByIP(String ip) {
        String result = null; // if country not found it will insert to a file named "null"
        try {
            result = databaseReader.city(InetAddress.getByName(ip)).getCountry().getName();
        } catch (Exception ignored) {}
        return result;
    }

    private static class IPAddress {

        private final int value;

        IPAddress(int value) {
            this.value = value;
        }

        IPAddress(String stringValue) {
            String[] parts = stringValue.split("\\.");
            if (parts.length != 4) {
                throw new IllegalArgumentException();
            }
            value =
                    (Integer.parseInt(parts[0], 10) << (8 * 3)) & 0xFF000000 |
                    (Integer.parseInt(parts[1], 10) << (8 * 2)) & 0x00FF0000 |
                    (Integer.parseInt(parts[2], 10) << (8 * 1)) & 0x0000FF00 |
                    (Integer.parseInt(parts[3], 10) << (8 * 0)) & 0x000000FF;
        }

        int getOctet(int i) {

            if (i < 0 || i >= 4) throw new IndexOutOfBoundsException();

            return (value >> (i * 8)) & 0x000000FF;
        }

        public String toString() {
            StringBuilder sb = new StringBuilder();

            for (int i = 3; i >= 0; --i) {
                sb.append(getOctet(i));
                if (i != 0) sb.append(".");
            }

            return sb.toString();
        }

        @Override
        public boolean equals(Object obj) {
            return obj instanceof IPAddress && value == ((IPAddress) obj).value;
        }

        @Override
        public int hashCode() {
            return value;
        }

        IPAddress next() {
            return new IPAddress(value + 1);
        }

    }
}

Iterated over 200.57.200.1..200.71.255.197 for test purpose, took 25seconds on on 16gb RAM 8 core pc
Results map :

• Number of lines | Country (file name, null means not found)
  320824 Argentina
  288766 Mexico
  98304 Peru
  37896 Colombia
  28672 Chile
  27584 Venezuela
  25600 Ecuador
  23840 United States
  18432 Bolivia
  16704 Uruguay
  16384 Nicaragua
  6208 Brazil
  6144 Panama
  4096 Paraguay
  3160 Honduras
  2048 null
  2048 Dominican Republic
  2048 Costa Rica
  1991 Bonaire, Sint Eustatius, and Saba
  768 British Virgin Islands
  256 Curaçao
  8 Italy

  931781 total