Clozure Common-Lisp (CCL), for five years now, has shipped with a fully ported distribution of JFLI (JFLI previously depended on the LispWorks FFI) as a standard component of the "examples" provided with the CCL source distribution. JFLI (by Rich Hickey, creator of Clojure) uses an in-process model and will likely be at least an order of magnitude more performant than anything you might put together from the model employed by Hickey's next attempt, a more widely compatible socket-based solution he named FOIL.
Have look at the following URL to browse the current JFLI source code as it currently exists in the Clozure development trunk:
https://github.com/Clozure/ccl/tree/master/examples/jfli
Rich Hickey introduced JFLI with the following summary of the approach he had taken (Substitute CCL's FFI where he references LW-FFI obviously):
My objective was to provide comprehensive, safe, dynamic and Lisp-y access to Java and Java libraries as if they were Lisp libraries, for use in Lisp programs, i.e. with an emphasis on working in Lisp rather than in Java. The approach I took was to embed a JVM instance in the Lisp process using JNI. I was able to do this using LispWorks' own FLI and no C (or Java! *) code, which is a tribute to the LW FLI. On top of the JNI layer (essentially a wrapper around the entire JNI API), I built this user-level API using Java Reflection.