JNLP is Java Network Launch Protocol that enables an application on the client to be launched using resources from a server. A JNLP (
.jnlp) file is associated with Java Web Start and needs to be executed by the
javaws program. On running javaws, it downloads the necessary classes from the web and uses them to launch the program.
On Ubuntu, a JNLP file should be launched using the IcedTea Java Web Start when you click it in the browser or after downloading it in Nautilus.
If this does not work, find out if the javaws executable is available. You may need to install the
$ sudo apt install icedtea-netx
Launch the JNLP file:
$ javaws foobar.jnlp
Tried with: icedtea-netx 1.6.2-3.1ubuntu3 and Ubuntu 18.04