ServiceLocator can't find an implementation in common-pool workers

Hi, I’ve noticed that we can’t read/create a token in a worker from ForkJoinPool.commonPool() in Spring’s uber-jar application because ServiceLocator can’t find an implementation for that (looks like there is a problem with context class loader related to the thread).

Example (it will throw UnavailableImplementationException for Serializer.class):

ForkJoinPool.commonPool()
        .execute(() -> Jwts.builder()
                .setClaims(Map.of(Claims.SUBJECT, "subject"))
                .compact());

Currently, I have a workaround to that by providing my own serializer (like this https://github.com/jwtk/jjwt#jackson-json-processor).

[lhazlewood]

I also want to say thank you to @timsazon for the sample project! That’s so helpful!

[bdemers]

@lhazlewood, I didn’t use a classloader, but I did mimic the “accessor” model that Classes uses. Let’s move the implementation discussion over to #574

(I just tested this out on @timsazon’s sample project)