Can QUARKUS use a generic library?

Question

Can QUARKUS applications add generic library dependencies? (Eg Guava) Or do I have to create all dependencies as QUARKUS EXTENSION?

Answer 1

If you run your Quarkus application on a regular JVM, all Java libraries should work as usual, and you can add them as regular dependencies.

It is when you enter the realm of AOT compilation to native binaries using GraalVM when things become interesting. Some Java libraries will work just fine without a single change, but a lot of Java libraries use features that are not supported in that environment; see https://github.com/oracle/graal/blob/master/substratevm/LIMITATIONS.md for details. If you hit those limitations, in the Quarkus context it's probably best to write an extension, because it nicely encapsulates everything you need to do to make the library work (be it reflection configuration, code substitutions, etc.)