Wikipedia
GeoTools
GeoTools is a free software ( LGPL) GIS toolkit for developing standards compliant solutions. It provides an implementation of Open Geospatial Consortium (OGC) specifications as they are developed. GeoTools is a contributor to the GeoAPI project - a vendor-neutral set of Java interfaces derived from OGC specifications - and implements a subset of those.
It is written in Java and currently is under active development. It is used by GeoServer, uDig, Geopublisher, 52N, Geomajas and many proprietary projects.