My fork of MaxMind's geoip-api v1 (legacy format) is at github.com/davipt/geoip-api-java.
Albeit the v1 dataset is considered legacy and the new v2 mmdb should be used, some information is lacking or not as easily accesible on the new dataset, so we stuck to the legacy database and library.
This fork contains performance optimizations for high volume multi-threaded applications, namely by removing the synchronized on calls where the data is only being read and only locking the code if the database is reloaded on-the-fly.