Java: convert int to InetAddress

Question

I have an int which contains an IP address in network byte order, which I would like to convert to an InetAddress object. I see that there is an InetAddress constructor that takes a byte[], is it necessary to convert the int to a byte[] first, or is there another way?

Solution 1

This should work:

int ipAddress = ....
byte[] bytes = BigInteger.valueOf(ipAddress).toByteArray();
InetAddress address = InetAddress.getByAddress(bytes);

You might have to swap the order of the byte array, I can't figure out if the array will be generated in the correct order.

Solution 2

Tested and working:

int ip  = ... ;
String ipStr = 
  String.format("%d.%d.%d.%d",
         (ip & 0xff),   
         (ip >> 8 & 0xff),             
         (ip >> 16 & 0xff),    
         (ip >> 24 & 0xff));

Solution 3

I think that this code is simpler:

static public byte[] toIPByteArray(int addr){
        return new byte[]{(byte)addr,(byte)(addr>>>8),(byte)(addr>>>16),(byte)(addr>>>24)};
    }

static public InetAddress toInetAddress(int addr){
    try {
        return InetAddress.getByAddress(toIPByteArray(addr));
    } catch (UnknownHostException e) {
        //should never happen
        return null;
    }
}

Solution 4

If you're using Google's Guava libraries, InetAddresses.fromInteger does exactly what you want. Api docs are here

If you'd rather write your own conversion function, you can do something like what @aalmeida suggests, except be sure to put the bytes in the right order (most significant byte first).

Solution 5

public static byte[] int32toBytes(int hex) {
    byte[] b = new byte[4];
    b[0] = (byte) ((hex & 0xFF000000) >> 24);
    b[1] = (byte) ((hex & 0x00FF0000) >> 16);
    b[2] = (byte) ((hex & 0x0000FF00) >> 8);
    b[3] = (byte) (hex & 0x000000FF);
    return b;

}

you can use this function to turn int to bytes;

View more solutions

Comments

[BalusC]

Can you post an example how this int look like and how its string representation should look like? I can't imagine how to put 255255255255 in an int, it would overflow.

[skaffman]

@BalusC: A IPv4 address is just a 32 bit number, it's just that it's usually represented as 4 8-bit values. The information fits just fine in 32 bits, though.

[iny]

Remember that, if you want to ever support IPv6, you can't use single int to handle IP addresses.

[BalusC]

He was asking for int-to-bytearray, not int-to-string. Also your words "this may work try" makes me think that you just googled blind and copypasted random function? Why?

[kdt]

That does indeed still require swapping the order of the byte array. However, it turns out my input was actually in host order after all! Thanks.

[user85421]

I don't think an additional leading sign bit will be a problem, but missing bytes if the address is in the range 0.0.0.0 - 0.127.255.255 and 255.128.0.0 - 255.255.255.255

[user85421]

will not work for addresses in the range 0.0.0.0 - 0.127.255.255 and 255.128.0.0 - 255.255.255.255: bytes will have less than 4 elements

[Dennis Laumen]

Sorry, I'm not an expert in this field. Could you elaborate on your comment? I'm afraid I'm missing the point (and could potentially have a bug in my code ;) ).

[aij]

@NikolayKuznetsov Because those ranges would result in a byte array of size 3 or less, whereas InetAddress requires the array to be of size 4 or 16.

[aij]

@DennisLaumen You do. Try for example, 0, 42, or -42. You should get 0.0.0.0, 0.0.0.42, and 255.255.255.214. Instead you'll get an exception. See also en.wikipedia.org/wiki/Twos_complement

[aij]

This is almost right, but you got the order of the bytes backwards: docs.oracle.com/javase/7/docs/api/java/net/…

[toom]

Dangerous. Does not work, for instance for 0.0.0.0. Not reliable!

[redbeam_]

the link in your answer is broken

[aij]

@redbeam_ Updated.

[Mr. Kevin Thomas]

This converts the bytes in the wrong order. It would work for little-endian ints, but the question asked about "network byte order" which is big-endian as are ints in Java. The correct order is: String.format("%d.%d.%d.%d", (ip >> 24 & 0xff), (ip >> 16 & 0xff), (ip >> 8 & 0xff), (ip & 0xff));