Calculate Network Subnet Range efficiently!

import lombok.AccessLevel;
import lombok.Builder;
import lombok.Data;
import lombok.experimental.Accessors;

import java.util.List;
import java.util.regex.Pattern;
import java.util.stream.IntStream;

import static com.varra.auth.utils.CommonUtils.ipStringToLong;
import static java.lang.Integer.parseInt;
import static java.lang.Math.pow;
import static java.util.stream.Collectors.toList;

/**
 * TODO Description go here.
 *
 * @author Rajakrishna V. Reddy
 * @version 1.0
 */
public class SubnetCalculator {

    private static final Pattern CIDR_PATTERN = Pattern.compile("/");

    @Accessors(chain = true, fluent = true)
    @Data
    @Builder(access = AccessLevel.PRIVATE)
    public static class Subnet {
        private final int cidr;
        private final int ipCount;
        private final int startIp;
        private final int endIp;

        public static Subnet of(final String ipWithCIDR)
        {
            final String[] ipWithCIDRTokens = CIDR_PATTERN.split(ipWithCIDR);
            final int numericCIDR = parseInt(ipWithCIDRTokens[1]);
            final int netmaskNumeric = 0xffffffff << (32 - numericCIDR);
            final int numberOfIPs = (int) pow(2, 32 - numericCIDR) - 1;
            final int baseIP = (int)ipStringToLong(ipWithCIDRTokens[0]) & netmaskNumeric;
            return Subnet.builder().cidr(numericCIDR).ipCount(numberOfIPs).startIp(baseIP).endIp(baseIP + numberOfIPs -1).build();
        }
    }

    /**
     * Specify IP in CIDR format like: new IPv4("10.1.0.25/16");
     *
     * @param ipWithCIDR ""
     */
    public static List<String> getAvailableIps(final String ipWithCIDR) throws NumberFormatException {
        return getAvailableIpsAsIntegers(ipWithCIDR).mapToObj(CommonUtils::ipLongToString).collect(toList());
    }

    /**
     * Specify IP in CIDR format like: new IPv4("10.1.0.25/16");
     *
     * @param ipWithCIDR ""
     * @return IntStream Stream of ips as integers
     */
    public static IntStream getAvailableIpsAsIntegers(final String ipWithCIDR) throws NumberFormatException {
        final Subnet subnet = Subnet.of(ipWithCIDR);
        return IntStream.range(1, subnet.ipCount()).map(i -> i + subnet.startIp());
    }

    public static boolean isIpWithInSubnet(final String ipWithCIDR, final String ip) throws NumberFormatException {
        final Subnet subnet = Subnet.of(ipWithCIDR);
        final int ipAsInt = (int) ipStringToLong(ip);
        return subnet.startIp() <= ipAsInt && ipAsInt <= subnet.endIp();
    }
}