Java IP address for the internal network IP or public network IP method

This article illustrates how Java determines whether an IP address is an Intranet IP or a public IP address. Share with you for your reference. Specific analysis is as follows:

In the TCP/IP protocol, three IP address regions are reserved as private addresses, and their address ranges are as follows:

10.0.0.0 ~ 10.255.255.255
172.16.0.0/ 12:17 2.16.0.0 ~ 172.31.255.255
192.168.0.0/16:19 2.168.0.0 ~ 192.168.255.255

So, directly on the code:

public static boolean internalIp(String ip) {

    byte[] addr = IPAddressUtil.textToNumericFormatV4(ip);

    return internalIp(addr);

}
public static boolean internalIp(byte[] addr) {

    final byte b0 = addr[0];

    final byte b1 = addr[1];

    //10.x.x.x/8

    final byte SECTION_1 = 0x0A;

    //172.16.x.x/12

    final byte SECTION_2 = (byte) 0xAC;

    final byte SECTION_3 = (byte) 0x10;

    final byte SECTION_4 = (byte) 0x1F;

    //192.168.x.x/16

    final byte SECTION_5 = (byte) 0xC0;

    final byte SECTION_6 = (byte) 0xA8;

    switch (b0) {

        case SECTION_1:

            return true;

        case SECTION_2:

            if (b1 >= SECTION_3 && b1 <= SECTION_4) {

                return true;

            }

        case SECTION_5:

            switch (b1) {

                case SECTION_6:

                    return true;

            }

        default:

            return false;

    }

}

I hope this article has been helpful to your Java programming.