This seems to be a problem with name resolution (DNS lookup). Once gotten an answer the answer is cached for a while until a new lookup is required.
Who's calling the webservice?
An application which is running on JBoss calls an external webservice?
Or do you run a client program calling a webservice hosted on JBoss?
Try "nslookup <hostname>" on the computer where the webservice access is happening. Does this return immediately also on first access?
A REST-Webservice, running on the JBoss is calling an external webservice.
I tried nslookup on the JBoss server host with no delay on the first access.