Java InetAddress Create getSubnetPrefix(InetAddress ip, int maskLen)

Description

Given an IP address and a prefix network mask length, it returns the equivalent subnet prefix IP address Example: for ip = "172.28.30.254" and maskLen = 25 it will return "172.28.30.128"

License

Open Source License

Parameter

Parameter	Description
ip	the IP address in InetAddress form
maskLen	the length of the prefix network mask

Return

the subnet prefix IP address in InetAddress form

Declaration

public static InetAddress getSubnetPrefix(InetAddress ip, int maskLen)

Method Source Code

//package com.java2s;
/*//from  w  w  w .j  a  va2  s .c om
 * Copyright (c) 2013-2014 Cisco Systems, Inc. and others.  All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v1.0 which accompanies this distribution,
 * and is available at http://www.eclipse.org/legal/epl-v10.html
 */

import java.net.InetAddress;
import java.net.UnknownHostException;

public class Main {
    /**
     * Given an IP address and a prefix network mask length, it returns the
     * equivalent subnet prefix IP address Example: for ip = "172.28.30.254" and
     * maskLen = 25 it will return "172.28.30.128"
     *
     * @param ip      the IP address in InetAddress form
     * @param maskLen the length of the prefix network mask
     * @return the subnet prefix IP address in InetAddress form
     */
    public static InetAddress getSubnetPrefix(InetAddress ip, int maskLen) {
        int bytes = maskLen / 8;
        int bits = maskLen % 8;
        byte modifiedByte;
        byte[] sn = ip.getAddress();
        if (bits > 0) {
            modifiedByte = (byte) (sn[bytes] >> (8 - bits));
            sn[bytes] = (byte) (modifiedByte << (8 - bits));
            bytes++;
        }
        for (; bytes < sn.length; bytes++) {
            sn[bytes] = (byte) (0);
        }
        try {
            return InetAddress.getByAddress(sn);
        } catch (UnknownHostException e) {
            return null;
        }
    }
}