I'm currently working on a research in VANETs area, and I'm looking for a tool supports Java programming language in order to implement a routing protocol.
OMNET++ with VEINS (http://veins.car2x.org/) or NS-3 (https://www.nsnam.org/) are suitable for working with VANET. The ONE simulator (https://www.netlab.tkk.fi/tutkimus/dtn/theone/) is implemented in Java, but this simulator isn't specific for VANET. Maybe it's worth it in your project.