make servlet3 + spring webmvc + jaxrs 2.0 indy compatible

[SylvainJuge]

part of #11457

[SylvainJuge]

[for reviewer] this is an edge-case where the inlined advice will be able to directly call the OpenTelemetryHandlerMappingFilter class directly and with indy we get a proxy instance that needs to be unwrapped (thus the delegate fields needs to be made public for simplicity).

[JonasKunz]

I'd suggest to add a TODO here to drop this branch when we remove support for inlined advice then maybe?

[SylvainJuge]

[for reviewer] this is an edge-case where the inlined advice will be able to directly call the OpenTelemetryHandlerMappingFilter class directly and with indy we get a proxy instance that needs to be unwrapped (thus the delegate fields needs to be made public for simplicity).

[JonasKunz]

I'd suggest to add a TODO here to drop this branch when we remove support for inlined advice then maybe?

[laurit]

Imo instead of doing the reflection here there should be an API to do this. Something that would unwrap the object when it is proxy and return the input when it is not. So you could write OpenTelemetryHandlerMappingFilter filter = = (OpenTelemetryHandlerMappingFilter) unwrap(springCtx.getBean("otelAutoDispatcherFilter"));
I guess using the reflection as currently is fine for start. Instead of making the delegate field public I'd probably try to make the proxy instance implement an interface that allow unwrapping. If needed that interface could be hidden from reflection

opentelemetry-java-instrumentation/instrumentation/internal/internal-reflection/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/internal/reflection/ReflectionHelper.java

Line 59 in 647fc45

public static Class<?>[] filterInterfaces(Class<?>[] interfaces, Class<?> containingClass) {

Idk how hard all of this would be to implement.