Lots of those sites will put you on a blacklist if you hit them too many times, i.e. too frequently.
In general a better solution would be to use the system UPnP libraries to detect and query your NAT router, but that would be platform-dependent and require a wrapper of some sort.
There do seem to be some UPnP libraries written in Java though. I just don't know anything about them. Here is one example:
@tucano2000
Thanks for the update. This has happened with the server change at least once before. I am glad you got it to work. This is something that will have to be adjusted by anyone using "exip" for accessing the external IP. Relying on them not to change the address is what we hope for but if they do. It will be back to changing it again or going to another external IP service.