Neo4j is an open-source graph database, implemented in Java. JGraphT is a free Java graph library that provides mathematical graph-theory objects and algorithms. JGraphT is a well fitting data model for Neo4j query results as well as it provides a rich pool of algorithms to process it. With jgrapht-neo4j-client you can get a JGraphT graph object as a result from a Neo4j Cypher query.
You can read more about this project in this blog post: Neo4j and JGraphT – A Perfect Team