Java – Convert IP address to Decimal Number

朱雀 2022-06-08 07:13 180阅读 0赞

### 1. IP Address to Decimal ###

We show you two ways to convert an IP address to a decimal number

*  Normal power of 256
 *  Bit shifting

#### 1.1 First Example – Power of 256 ####

The IP address is “base 256”, to convert 192.168.1.2 to decimal (base 10) the formula is:

> 192 x (256)^3 + 168 x (256)^2 + 1 x (256)^1 + 2 (256)^0 = ?  
> 3221225472 + 11010048 + 256 + 2 = 3232235778

public long ipToLong(String ipAddress) {
    
    String[] ipAddressInArray = ipAddress.split("\\.");
    
    long result = 0;
    for (int i = 0; i < ipAddressInArray.length; i++) {
    
        int power = 3 - i;
        int ip = Integer.parseInt(ipAddressInArray[i]);
        result += ip * Math.pow(256, power);
    
    }
    
    return result;
      }

Some developers prefer to use modular like this

> result += (Integer.parseInt(ipAddressInArray\[i\]) % 256 \* Math.pow(256, power));

#### 1.2 Second Example - Bit shifting ####

Review the binary bit shifting graph below :

public long ipToLong(String ipAddress) {
    
    long result = 0;
    
    String[] ipAddressInArray = ipAddress.split("\\.");
    
    for (int i = 3; i >= 0; i--) {
    
        long ip = Long.parseLong(ipAddressInArray[3 - i]);
    
        //left shifting 24,16,8,0 and bitwise OR
    
        //1. 192 << 24
        //1. 168 << 16
        //1. 1 << 8
        //1. 2 << 0
        result |= ip << (i * 8);
    
    }
    
    return result;
      }

192 00000000 00000000 00000000 11000000 -----------------------------------------------
    192 << 24   11000000 00000000 00000000 00000000
    Result      00000000 00000000 00000000 00000000
    Result |=   11000000 00000000 00000000 00000000
    
    168 00000000 00000000 00000000 10101000 -----------------------------------------------
    168 << 16   00000000 10101000 00000000 00000000
    Result      11000000 00000000 00000000 00000000
    Result |=   11000000 10101000 00000000 00000000
    
    1 00000000 00000000 00000000 00000001 -----------------------------------------------
    1   << 8    00000000 00000000 00000001 00000000
    Result      11000000 10101000 00000000 00000000
    Result |=   11000000 10101000 00000001 00000000
    
    2 00000000 00000000 00000000 00000010 -----------------------------------------------
    2 << 0      00000000 00000000 00000000 00000010
    Result      11000000 10101000 00000001 00000000
    Result |=   11000000 10101000 00000001 00000010

Convert the final binary code to decimal, by hand calculation :) ~

Result 11000000 10101000 00000001 00000010 index 0 - 31, start from right. 31(1),30(1),29,28,27,26,25,24,23(1),22,21(1),20,19(1),18,17,16,15,14,13,12,11,10,9,8(1),7,6,5,4,3,2,1(1),0 Decimal 1x2^31 + 1x2^30 + 1x2^23 + 1x2^21 + 1x2^19 + 1x2^8 + 1x2^1 2147483648 + 1073741824 + 8388608 + 2097152 + 524288 + 256 + 2 3232235778

### 2. Decimal to IP Address ###

We show you two bit shifting and “0xff” masking examples to convert a decimal number back to IP address. The bit shifting is very hard to explain in words, it’s better review the binary flows below :

#### 2.1 First Example. ####

//ip = 3232235778
      public String longToIp(long ip) {
    StringBuilder result = new StringBuilder(15);
    
    for (int i = 0; i < 4; i++) {
    
        result.insert(0,Long.toString(ip & 0xff));
    
        if (i < 3) {
            sb.insert(0,'.');
        }
    
        ip = ip >> 8;
    }
    return result.toString();
      }

Review the bit shifting flows :

3232235778      11000000 10101000 00000001 00000010
    
    <<Loop 1>> -----------------------------------------------------------
    ip              11000000 10101000 00000001 00000010
    & 0xff          00000000 00000000 00000000 11111111
    Result                  00000000 00000000 00000000 00000010 = 2
    Result Append           .2
     -------------------------> 8
    ip >> 8         00000000 11000000 10101000 00000001 {off 00000010}
    
    <<Loop 2>> -----------------------------------------------------------
    ip              00000000 11000000 10101000 00000001
    & 0xff          00000000 00000000 00000000 11111111
    Result                  00000000 00000000 00000000 00000001 = 1
    Result Append           1.2
     ----------------> 8
    ip >> 8         00000000 00000000 11000000 10101000 {off 00000001}
    
    <<Loop 3>> -----------------------------------------------------------
    ip              00000000 00000000 11000000 10101000
    & 0xff          00000000 00000000 00000000 11111111
    Result                  00000000 00000000 00000000 10101000 = 168
    Result Append           168.1.2
     -------> 8
    ip >> 8         00000000 00000000 00000000 11000000 {off 10101000}
    
    <<Loop 4>> -----------------------------------------------------------
    ip              00000000 00000000 00000000 11000000
    & 0xff          00000000 00000000 00000000 11111111
    Result                  00000000 00000000 00000000 11000000 = 192
    Result Append           192.168.1.2
     -----------> 8
    ip >> 8         00000000 00000000 00000000 00000000 {off 11000000}

#### 2.2 Second Example. ####

//ip = 3232235778
      public String longToIp(long ip) {
    
    return ((ip >> 24) & 0xFF) + "."
        + ((ip >> 16) & 0xFF) + "."
        + ((ip >> 8) & 0xFF) + "."
        + (ip & 0xFF);
    
      }

3232235778      11000000 10101000 00000001 00000010
    
    1. (ip >> 24) & 0xFF -----------------------------------------------------------
    ip              11000000 10101000 00000001 00000010
     -------------------------------------> 24
    ip >> 24                00000000 00000000 00000000 11000000 {off 10101000 00000001 00000010}
    & 0xff          00000000 00000000 00000000 11111111
    Result                  00000000 00000000 00000000 11000000 = 192
    
    2. (ip >> 16) & 0xFF -----------------------------------------------------------
    ip              11000000 10101000 00000001 00000010
     -------------------------------------> 16
    ip >> 16                00000000 00000000 11000000 10101000 {off 00000001 00000010}
    & 0xff          00000000 00000000 00000000 11111111
    Result                  00000000 00000000 00000000 10101000 = 168
    
    3. (ip >> 8) & 0xFF -----------------------------------------------------------
    ip              11000000 10101000 00000001 00000010
     --------------------------------------> 8
    ip >> 24                00000000 11000000 10101000 00000001 {off 00000010}
    & 0xff          00000000 00000000 00000000 11111111
    Result                  00000000 00000000 00000000 00000001 = 1
    
    4. ip & 0xFF -----------------------------------------------------------
    ip              11000000 10101000 00000001 00000010
    & 0xff          00000000 00000000 00000000 11111111
    Result                  00000000 00000000 00000000 00000010 = 2

### 3. Java Source Code ###

Full Java example to demonstrate above scenario :

package com.mkyong.core;
    
    public class JavaBitwiseExample {
    
        public static void main(String[] args) {
    
            JavaBitwiseExample obj = new JavaBitwiseExample();
    
            System.out.println("iptoLong : " + obj.ipToLong("192.168.1.2"));
            System.out.println("iptoLong2 : " + obj.ipToLong2("192.168.1.2"));
    
            System.out.println("longToIp : " + obj.longToIp(3232235778L));
            System.out.println("longToIp2 : " + obj.longToIp2(3232235778L));
    
        }
    
        // example : 192.168.1.2
        public long ipToLong(String ipAddress) {
    
            // ipAddressInArray[0] = 192
            String[] ipAddressInArray = ipAddress.split("\\.");
    
            long result = 0;
            for (int i = 0; i < ipAddressInArray.length; i++) {
    
                int power = 3 - i;
                int ip = Integer.parseInt(ipAddressInArray[i]);
    
                // 1. 192 * 256^3
                // 2. 168 * 256^2
                // 3. 1 * 256^1
                // 4. 2 * 256^0
                result += ip * Math.pow(256, power);
    
            }
    
            return result;
    
        }
    
        public long ipToLong2(String ipAddress) {
    
            long result = 0;
    
            String[] ipAddressInArray = ipAddress.split("\\.");
    
            for (int i = 3; i >= 0; i--) {
    
                long ip = Long.parseLong(ipAddressInArray[3 - i]);
    
                // left shifting 24,16,8,0 and bitwise OR
    
                // 1. 192 << 24
                // 1. 168 << 16
                // 1. 1 << 8
                // 1. 2 << 0
                result |= ip << (i * 8);
    
            }
    
            return result;
        }
    
        public String longToIp(long i) {
    
            return ((i >> 24) & 0xFF) +
                       "." + ((i >> 16) & 0xFF) +
                       "." + ((i >> 8) & 0xFF) +
                       "." + (i & 0xFF);
    
        }
    
        public String longToIp2(long ip) {
            StringBuilder sb = new StringBuilder(15);
    
            for (int i = 0; i < 4; i++) {
    
                // 1. 2
                // 2. 1
                // 3. 168
                // 4. 192
                sb.insert(0, Long.toString(ip & 0xff));
    
                if (i < 3) {
                    sb.insert(0, '.');
                }
    
                // 1. 192.168.1.2
                // 2. 192.168.1
                // 3. 192.168
                // 4. 192
                ip = ip >> 8;
    
            }
    
            return sb.toString();
        }
    
        /* private static void printPrettyBinary(String binary) { String s1 = String.format("%32s", binary).replace(' ', '0'); System.out.format("%8s %8s %8s %8s %n", s1.substring(0, 8), s1.substring(8, 16), s1.substring(16, 24), s1.substring(24, 32)); } */
    }

OUTPUT

iptoLong  : 3232235778
    iptoLong2 : 3232235778
    longToIp  : 192.168.1.2
    longToIp2 : 192.168.1.2

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