This is a fairly old source now (posted in 2016, work from 2013-2015) but people still use it - here it is mirrored and using gradle for project management.
Source and credits: https://rune-server.org/runescape-development/rs-503-client-and-server/downloads/618618-matrix-3-official-release-recommended-rs3-download-830-a.html
Compatible OpenRS2 cache: https://archive.openrs2.org/caches/runescape/484
First - download the cache and place it under the Server project, inside a new folder data/cache/. You should see data/cache/main_file_cache.dat2.
Make sure you open the server and the client folder in separate IntelliJ windows. They are separate projects.
I kept the old batch scripts so they still work if you prefer that approach.
If you want to launch through IntelliJ, add a few run configurations using Gradle as the target:
runGame: Start the game server
runLogin: Start the login server
You don't have to run IntelliJ to start the client if you just want to play.
I kept the old batch script, use that if you prefer that approach or don't need to make any client changes.
If you want to launch through IntelliJ, add a run configuration using Gradle as the target:
run: Start the client