Is there an easy way to convert String to Inetaddress in Java?

Question

I am trying to convert strings into Inetaddress. I am not trying to resolve hostnames: the strings are ipv4 addresses. Does InetAddress.getByName(String host) work? Or do I have to manually parse it?

score 26 · Accepted Answer · edited Dec 10 '16 at 11:01

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com.google.common.net.InetAddresses.forString(String ipString) is better for this as it will not do a DNS lookup regardless of what string is passed to it.

edited Dec 10 '16 at 11:01

Flow

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answered Jun 15 '12 at 16:28

John Gardiner Myers

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This is part [of Guava](http://docs.guava-libraries.googlecode.com/git-history/v10.0.1/javadoc/com/google/common/net/InetAddresses.html). – Matthew Flaschen Jun 19 '12 at 16:37
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It should be `com.google.common.net.InetAddresses.forString` (with `InetAddresses` with uppercase A). SO won’t allow me to correct that in your answer, as the edit has to be at least 6 characters. ;-) Anyway, thanks, was looking for it, and yet again Guava saves the day. – silmeth Oct 20 '16 at 14:10

score 14 · Answer 2 · edited Dec 02 '14 at 00:06

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Yes, that will work. The API is very clear on this ("The host name can either be a machine name, such as "java.sun.com", or a textual representation of its IP address."), and of course you could easily check yourself.

edited Dec 02 '14 at 00:06

FujiRoyale

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answered Feb 22 '10 at 05:45

Matthew Flaschen

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Thanks, I looked up the api, and missed that line. – TiansHUo Feb 22 '10 at 05:49
Whats when host is a pattern like 192.168.0.*? Will that work too? Regarding to Inet4Address doc there seems support for this. – Sebastian Hoffmann Feb 24 '12 at 13:58
@Paranaix, no, it will throw a `IllegalArgumentException` with the message "invalid host wildcard specification" – Matthew Flaschen Feb 24 '12 at 16:24
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in particular, the documentation says: `If a literal IP address is supplied, only the validity of the address format is checked.` which I read as: 'if you specify a (dotted quad notation) IP address, no DNS lookup is performed'. – Andre Holzner Apr 03 '12 at 07:33
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The OP said "I am not trying to resolve hostnames"; if the input to `getByName()` is not a valid numeric IP address, but is a valid resolvable DNS name, the name will be resolved. That does not seem to be what the OP wants. – Raedwald Mar 28 '13 at 16:57
@Raedwald, he also said "the strings are ipv4 addresses". If the input is known to be just IP addresses, this should work fine. – Matthew Flaschen Mar 28 '13 at 20:00

wu-lee · Answer 3 · 2013-11-18T16:10:34.773

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Beware: it seems that parsing an invalid address such as InetAddress.getByName("999.999.999.999") will not result in an exception as one might expect from the documentation's phrase:

the validity of the address format is checked

Empirically, I find myself getting an InetAddress instance with the local machine's raw IP address and the invalid IP address as the host name. Certainly this was not what I expected!

edited Nov 18 '13 at 16:10

answered Nov 18 '13 at 13:29

wu-lee

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As of Java 7, this will throw an UnknownHostException; haven't checked earlier Javas, but I would expect an exception there as well. – Craig Trader Mar 12 '15 at 12:38
@CraigTrader, but if you look at the stack trace you will see that this is not actually a parsing exception, but Java tries to look this up as host name, which is somewhat worrying. – Marcono1234 Aug 10 '21 at 03:06
Because `999.999.999.999` is NOT a valid IPv4 address, Java asks the system's name server to resolve it as a hostname. Since there is no valid DNS entry for that IP address, you'll get an `UnknownHostException`. If you try this with a valid IPv4 address, you'll get a valid `InetAddress` object. – Craig Trader Aug 10 '21 at 15:14

score 1 · Answer 4 · edited May 23 '17 at 12:25

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You could try using a regular expression to filter-out non-numeric IP addresses before passing the String to getByName(). Then getByName() will not try name resolution.

edited May 23 '17 at 12:25

Community

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answered Mar 28 '13 at 17:06

Raedwald

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score 0 · Answer 5 · answered Dec 18 '17 at 02:27

The open-source IPAddress Java library will validate all standard representations of IPv6 and IPv4 and will do so without DNS lookup. Disclaimer: I am the project manager of that library.

The following code will do what you are requesting:

     String s = "1.2.3.4";
     try {
            IPAddressString str = new IPAddressString(s);
            IPAddress addr = str.toAddress();
            InetAddress inetAddress = addr.toInetAddress(); //IPv4 or IPv6
            if(addr.isIPv4() || addr.isIPv4Convertible()) {//IPv4 specific
                IPv4Address ipv4Addr = addr.toIPv4();
                Inet4Address inetAddr = ipv4Addr.toInetAddress();
                //use address
            }
      } catch(AddressStringException e) {
            //e.getMessage has validation error
      }

Is there an easy way to convert String to Inetaddress in Java?

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