Is there a simple way to play Star Wars Jedi Knight : Jedi Academy in LAN?

It's fairly easy to host a server and then friends can join either on the same LAN or across the internet as well. There are a variety of different servers you can host, depending on the mods you have, but for standard JKA, use this: https://jkhub.org/files/file/391-jedi-academy-dedicated-server-for-win32/

Download and then put those files in your gamedata folder. Again, make sure you select the correct version. If you have the steam version, you should have v1.01. Otherwise, you have just v1.0 (unless you manually patched the game yourself, you would know).

To launch the server, just follow the instructions in readme.txt. You'll essentially be launching jampDed.exe, but there is a specific way to do it that you can't do simply by clicking on it. If all goes smoothly, as it should on a fresh install, your server will start in a command prompt window. Leave that open as this is your server in action. Close it and you kill the server. From here, you can connect directly to it, as can your friends on LAN. It should show up in your game's server list under the LAN category/

If you can't find your server in the LAN list, you can find your local ip easily by going into command prompt and typing ipconfig. This will reveal your connections and you should be able to isolate which one is yours. Back in game, once you know your local ip address, you can open the console shift+~ and type /connect yourIPhere. It's most likely something along the lines of 192.168.*.*. The asterisks represent numbers that could literally be anything between 0 and 255.

To customize your server settings, you can do so in base/server.cfg, which is one of the included files in the download above. The setup for server usage and basically the same for every mod you may wish to use, however, you'll have to follow their instructions for slight variations on the process.

So long as you are playing on a LAN, you won't need to do any port forwarding, but should you wish to open your game across the internet, you can do that as well. I won't detail that here, though, since that wasn't the original question.

Hopefully that gives you a brief overview how this works. The the it takes to launch the servers is almost nothing, but there's obviously a lot of little things you have to know in order to do it.