I have seen the same problem. Here is how I worked around it.
My machine is using DHCP. I modified my /etc/hosts file
FROM:
127.0.0.1 localhost
127.0.1.1 <my machine name>
TO:
127.0.0.1 localhost
127.0.0.1 <my machine name>
Log out, then log back in. (or restart the service from command line if you are more savvy)
This got rid of the UnknowHostException for me. Any of the asadmin command seems to work even with the exception stack, since it looks like it is defaulting to "localhost" anyway. Though it would have been nice if the error looks less scary.
Thanks,
Q^2
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