Classpaths in projects?

[NullPlane]

(WINDOWS, jdt.ls 1.9.0)
Need some help with projects.
I set up jdtls in my editor ecode and it works like a charm until I try to use a library from my university.
It came in a jar. When I open a single file it says non-project file - only syntax errors highlighted but when
I try to use my university's lib and open the whole folder as a project, it won't resolve anything outta there. I tried
adding a custom folder to %CLASSPATH% and putting it in there but no help.

I am forced to use ant so no maven etc.

Can I put it into a special folder with some name or anything? In the basedir I currently put it to .\res\dep but
obviously that is not found. It shall only be unpacked into lib before compiling but I'd love to do projects without
jdtls not finding my resources and marking them in red as errors as I'd need that to quickly find syntax problems.

How would I accomplish that? Is there some workaround or init value for such cases to give a folder with some jars?

[j-xella]

I have a similar situation on linux - we don't have maven etc... using old ant for builds, and specify dependencies via $CLASSPATH. jdtls does not seem to see the dependency jars, reporting errors when I use thsoe classes in my code...

[38leinaD]

This basically also similar question i asked: #3478
I really would like to understand what is the way to add jars to the classpath for simple project that does not use maven or gradle. with java making it simpler and simpler to get started with java (single source java files, ...) the natural next step is to be able to add a simple jar dependency without a build tool. i can do that in general with java and setting the classpath but for me this all breaks down when i want to use an editor to give me auto complete for classes and methods on those external jar classes. for vscode it seems to work to add the conventional lib folder containing jars, but it looks to me like that is a special feature of vscode only and not jdt in general!? at least it does not work in sublime jdt integration: sublimelsp/LSP-jdtls#59

[mickaelistria]

Have you tried adding a .classpath file similar to the one Eclipse IDE would use for such a project, and that would reference the CLASS_PATH variable?