Convert a String to InetAddress without DNS lookup

Question

I have a local IP address in dotted decimal notation in a String. I want to convert it to an InetAddress to feed it to Socket, but I need to do it without doing a DNS lookup (because this might cause lengthy timeouts).

Is there a ready method for that, or do I need to split the String and create the InetAddress from its bytes?

Update The factory methods InetAddress.getByName() and InetAddress.getByAddress() don't seem to be a good fit, as they both also accept hostnames such as java.sun.com. There is no saying if they will try to contact a DNS server in their implementation.

possible duplicate of Is there an easy way to convert String to Inetaddress in Java? — Zelldon
– Zelldon, Commented Dec 11, 2013 at 12:49
@Zelldon, agreed. I don't want to use an entire library for just this features though. — Bart Friederichs
– Bart Friederichs, Commented Dec 11, 2013 at 12:51
@Zelldon yes but different answer. I want to make 100% sure there is no network activity going on. — Bart Friederichs
– Bart Friederichs, Commented Dec 11, 2013 at 13:00

Kara · Accepted Answer · 2017-04-17 16:10:19Z

30

Do like this

InetAddress inetAddress = InetAddress.getByName("192.168.0.105");

If a literal IP address is supplied, only the validity of the address format is checked.

java source code

// if host is an IP address, we won't do further lookup    
if (Character.digit(host.charAt(0), 16) != -1 || (host.charAt(0) == ':')) {

}

edited Apr 17, 2017 at 16:10

Kara

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answered Dec 11, 2013 at 12:50

Prabhakaran Ramaswamy

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12 Comments

Bart Friederichs Over a year ago

Is it guaranteed there will be no DNS going on (also no reverse DNS or whatever) ?

Prabhakaran Ramaswamy Over a year ago

@BartFriederichs As per java document there is no DNS verification if correct ip format is provided. Reference - docs.oracle.com/javase/7/docs/api/java/net/…

Alexey Odintsov Over a year ago

Source code says the same: 'if host is an IP address, we won't do further lookup'

nos Over a year ago

If the supplied string is in dotted quad format, it will not do a dns lookup. If you need to be sure, validate the string first, e.g. . stackoverflow.com/questions/5667371/validate-ip-address

Samitha Chathuranga Over a year ago

In my case, InetAddress address= InetAddress.getByName("www.sun.com"); runs correctly, but when I give a wrong host address as the argument such as "www.sunqqq.com" it gave exceptions. >>> java.net.UnknownHostException: www.sunqqq.com at java.net.Inet6AddressImpl.lookupAllHostAddr(Native Method) at java.net.InetAddress$1.lookupAllHostAddr(Unknown Source) at java.net.InetAddress.getAddressesFromNameService(Unknown Source) at java.net.InetAddress.getAllByName0(Unknown Source) at java.net.InetAddress.getAllByName(Unknown Source)....(more)

|

Matt Ball · Accepted Answer · 2017-04-21 14:08:02Z

7

You can use Guava's InetAddresses#forString() which is specifically documented for your use case:

Returns the InetAddress having the given string representation.
This deliberately avoids all nameservice lookups (e.g. no DNS).

(emphasis added)

edited Apr 21, 2017 at 14:08

answered Jan 11, 2017 at 22:24

Matt Ball

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Comments

Sean F · Accepted Answer · 2018-01-11 22:40:52Z

3

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 str = "fe80:0:0:0:f06c:31b8:cd17:5a44";
        try {
            IPAddressString str = new IPAddressString(str);
            IPAddress addr = str.toAddress();//throws if invalid, without a DNS lookup
            InetAddress inetAddr = addr.toInetAddress();//convert valid address
            //use address
        } catch(AddressStringException e) {
            //e.getMessage has validation error
        }

edited Jan 11, 2018 at 22:40

answered Dec 18, 2017 at 2:22

Sean F

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Comments

Ali · Accepted Answer · 2013-12-11 12:51:03Z

1

You can do this by using the getByName method. for example:

InetAddress localhost = InetAddress.getByName("127.0.0.1")

As it is described on the java docs:

The host name can either be a machine name, such as "java.sun.com", or a textual representation of its IP address. If a literal IP address is supplied, only the validity of the address format is checked.

answered Dec 11, 2013 at 12:51

Ali

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3 Comments

Samitha Chathuranga Over a year ago

In my case, InetAddress address= InetAddress.getByName("www.sun.com"); runs correctly, but when I give a wrong host address as the argument such as "www.sunqqq.com" it gave exceptions. >>> java.net.UnknownHostException: www.sunqqq.com at java.net.Inet6AddressImpl.lookupAllHostAddr(Native Method) at java.net.InetAddress$1.lookupAllHostAddr(Unknown Source) at java.net.InetAddress.getAddressesFromNameService(Unknown Source) at java.net.InetAddress.getAllByName0(Unknown Source) at java.net.InetAddress.getAllByName(Unknown Source)....(more) –

Samitha Chathuranga Over a year ago

So does it means that getByName() method do the DNS checkups??? As it seems the validity of the host address also have checked???

Ali Over a year ago

Yes. if you give a host name to getByName, it perform DNS lookup. but if an IP address is provided it only checks for the validity of the IP (string format).

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