Small Spring Boot 3.2 application to test and visualize the classloading problems that we're currently facing.

Steps to reproduce

gradle clean build

java -jar build/libs/cnf-0.0.1-SNAPSHOT.jar

Hint

The following problem ...

• does not occur when running the application within an IDE (e.g. IntelliJ) or via gradle bootRun.
• only occurs when running the application via java -jar build/libs/cnf-0.0.1-SNAPSHOT.jar and therefore using the Spring Boot classloader.
• is the same for Spring Boot 3.0 and 2.7.

Output (manually rearranged for better readability)

...
[405] - [ForkJoinPool.commonPool-worker-5] - Create JAXBContext with classloader jdk.internal.loader.ClassLoaders$AppClassLoader@531d72ca
[405] - [ForkJoinPool.commonPool-worker-5] - ERROR creating JAXBContext: java.lang.ClassNotFoundException: org.glassfish.jaxb.runtime.v2.ContextFactory
[405] - [ForkJoinPool.commonPool-worker-5] - BUT successful Class.forName("org.glassfish.jaxb.runtime.v2.ContextFactory")
...
[328] - [main] - Create JAXBContext with classloader org.springframework.boot.loader.launch.LaunchedClassLoader@2ff4acd0
[328] - [main] - JAXBContext created
...

It easy to see that crating the JAXBContext by the main thread works fine while it fails if done by a worker thread. It's also obvious that the main thread uses the Spring Boot classloader while the worker threads use the JDK AppClassLoader.

What is confusing

When creating the JAXBContext fails because of java.lang.ClassNotFoundException: org.glassfish.jaxb.runtime.v2.ContextFactory we try to load exactly this class via Class.forName("org.glassfish.jaxb.runtime.v2.ContextFactory"); which succeeds. How is this possible?

I'm aware of the Spring Boot issue describing this problem (spring-projects/spring-boot#15737) but are quite unsure how to fix this problem in our application.