That isn't really necessary. So long as your domain is properly configured in your network subsystem (e.g. in /etc/resolv.conf), attempting to resolve "www" is equivalent to resolving "www.example.com".

If you want to skip the step of actually attempting to resolve the hostnames, you can try to parse /etc/resolv.conf yourself and tack on each of the 'search' or 'domain' items (not sure what all is used), since you could technically have more than one. But if it's a custom app just for 1 location/purpose, I guess you could hard-code it without worry.