JettyReactiveClient NoClassDefFoundError in tests

Solution 1:

+--- org.eclipse.jetty:jetty-reactive-httpclient:3.0.4
|    +--- org.reactivestreams:reactive-streams:1.0.3
|    +--- org.eclipse.jetty:jetty-client:11.0.6 -> 9.4.44.v20210927

You have specified jetty-reactive-httpclient version 3.0.4

That requires Jetty 11 specific behaviors. You cannot downgrade Jetty arbitrarily like that.

As noted in the README for jetty-reactive-httpclient ...

https://github.com/jetty-project/jetty-reactive-httpclient/blob/1.1.x/README.md

Reactive Client Versions Java Min Version Jetty Min Version
1.1.x Java 8 Jetty 9.4.x
2.0.x Java 11 Jetty 10.0.x
3.0.x Java 11 Jetty 11.0.x

If you have to stick with Jetty 9 for whatever reason, then you should stick with the jetty-reactive-httpclient in the version range 1.1.x