Java and IPv6

Inet6Address

The class java.net.InetAddress has two subclasses

java.net.Inet4Address
java.net.Inet6Address

These cannot be instantiated directly, but are obtained from the "factory" methods such as


InetAddress.getByName(...)

If your network stack is configured to use IPv6, you get an Inet6Address , otherwise you get an Inet4Address .

You can check if you have an IPv6 address by


if (address instanceof Inet6Address) ...

You can check if a socket uses IPv6 by


if (socket.getLocalAddress() instanceof Inet6Address) ...

LocalHost

The IPv4 localhost is 127.0.0.1. The IPv6 localhost is 0:0:0:0:0:0:0:1

Other

There are methods to tell if an IPv6 address is compatable with an IPv4 address, and some properties that can be set to tell the JVM to prefer IPv4 or IPv6. Apart from that, there appears to be little that Java gives you.

Jan Newmarch <jan@newmarch.name>

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