After upgrading to the latest version of Debian squeeze/sid, I was not able to use the networking in java.

If you get:

[2/16/10 10:39 AM] Exception occurred:
java.net.SocketException: Network is unreachable
at java.net.PlainSocketImpl.socketConnect(Native Method)
at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:333)
at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:195)
at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:182)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:366)
at java.net.Socket.connect(Socket.java:525)


then you should disable ipv6. To do that just edit: /etc/sysctl.d/bindv6only.conf
and change

net.ipv6.bindv6only = 1
to
net.ipv6.bindv6only = 0

Now just run:

sudo invoke-rc.d procps restart


More Info: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=560044

Success !