How are you specifying the dependency on the JAR, and did you check that the JAR contains a pom.xml file?

I’ve since found out that the directory structure inside my jar is not as intended… so sorry to bother you. Also no, I don’t have a pom.xml. I have this in my deps.edn

dk.zoren/jar {:local/root "libs/BTree.jar"}

I get Unsupported class file major version 61 after fixing the directory layout inside the jar. Thank you, and again sorry to bother.

The latter says you have some code compiled on a more recent JDK than the one you're trying to run it on. 61 is JDK 17, so you'll need at least JDK 17 to run this.

Yes I found out. But I actually don’t really understand how it happend. I did compile the jar with java 17 and inside the vscode REPL the system property said "java.runtime.version" "17.0.5+8"

Now I’ve use asdf to install java and restarted VSCode, that fixed it for me.