ClassCastException from ResteasyClientClassicProvider #38996

The problem is the class loader. I have both cxf-rt-rs-client and resteasy-client being included in my project. The only way around this was to exclude cxf-rt-rs-client completely from my project. When I did this I solved all my problems.

However, if there is ever a need for a dependency to use cxf-rt-rs-client I'll have a serious problem. Somehow, there has to be a way somewhere in this tech stack to give the class loader a hint of which client class to use.

This is a serious problem and I don't know who to put a bug ticket towards.

Did you pass in a Client to the KeycloakBuilder, or did you let it create one?

I passed in a jakarta.ws.rs.client.Client to KeycloakBuilder using Jakarta API. This is basically what I did.

Client client = ResteasyClientBuilder.newBuilder()
.readTimeout(socketTimeout, TimeUnit.MILLISECONDS)
.connectTimeout(establishConnectionTimeout, TimeUnit.MILLISECONDS)
.trustStore(keyStore)
.build();

Keycloak keycloak = KeycloakBuilder.builder()
.clientId(clientId)
.clientSecret(clientSecret)
.grantType(OAuth2Constants.CLIENT_CREDENTIALS)
.realm(realm)
.serverUrl(serverUrl)
.resteasyClient(client)
.build();

Sorry, I got ahead of myself (typing directly in github, rather than in the IDE). Yes, you'll have to use the underlying apis more directly:

Client client = ClientBuilderWrapper.create(null, false).register(JacksonProvider.class, 100)
  .readTimeout(socketTimeout, TimeUnit.MILLISECONDS)
  .connectTimeout(establishConnectionTimeout, TimeUnit.MILLISECONDS)
  .trustStore(keyStore)
  .build();

This solution didn't work. The only way I could resolve this was by complete exclusion of cxf-rt-rs-client such that resteasy-client becomes the definitive for client creation and resolution (see https://github.com/orgs/resteasy/discussions/4538).

As fyi, I never used JacksonProvider class directly as you have provided in the example code. I have a custom class implementation that extended off ResteasyJackson2Provider class in my version.

This solution didn't work.

Do you want to share why / debug further?

As fyi, I never used JacksonProvider class directly as you have provided in the example code. I have a custom class implementation that extended off ResteasyJackson2Provider class in my version.

Sounds fine. For those following this discussion - you need to register an appropriate JacksonProvider to prevent situations described in #40231

The issue I believe was an RESTEasy issue. I posted recently how I resolved the issue (https://github.com/orgs/resteasy/discussions/4538#discussioncomment-13435733). I believe RESTEasy has a bug and needs to fix org.jboss.resteasy.client.jaxrs.ProxyBuilder.

However, I do find it strange that Thread.currentThread().getContextClassLoader() was not able to get the correct context and ProxyBuilder.class.getClassLoader() was the only way to appropriately retrieve the class in my tech stack.

Thread.currentThread().getContextClassLoader()

That will be managed by spring / jetty. It's certainly possible that it can be different than the classloader used specifically to load the ProxyBuilder class - as that will depend heavily on where there dependency is packaged.