Geohash utitlies in java
The Esri Geometry API for Java enables developers to write custom applications for analysis of spatial data. This API is used in the Esri GIS Tools for Hadoop and other 3rd-party data processing solutions.
Open source routing engine for OpenStreetMap. Use it as Java library or standalone web server.
The JTS Topology Suite is a Java library for creating and manipulating vector geometry.
Vector map library and writer - running on Android and Desktop.
LocationTech Spatial4j: A Geospatial Library for Java