UNIX socket implementation for Java?
Checkout the JUDS library. It is a Java Unix Domain Socket library...
You could use junixsocket: https://github.com/kohlschutter/junixsocket
It already provides code for connecting to MySQL from Java (Connector/J) via Unix sockets.
One big advantage compared to other implementations is that junixsocket uses the standard Java Socket API.
As the original kohlschutter/junixsocket , mentioned in another answer seems to be dead, you can check out its forks.
Especially fiken/junixsocket looks promising. Its author has added support for connection to PostgreSQL using unix socket via pgjdbc, for example.