JPL is integrated into the full SWI-Prolog distribution starting with
version 5.4.x, including binaries for MS-Windows and a Linux RPM.
Documentation is -like all integrated packages-, available from the
SWI-Prolog website and from the local manual
browser under Help/Package documentation. Examples are included in the
doc/packages/examples/jpl relative to the installation
directory. These examples include embedding Prolog in Java as well as
the other way around.
JPL is actively maintained by Paul Singleton.