quarkusio/quarkus · error · RuntimeException

Could not find provider class: " + name

Error message

Could not find provider class: " + name

What it means

Thrown by RestClientCDIDelegateBuilder.providerClassForName when a JAX-RS provider class name configured for the rest client (via @RegisterProvider or registerProviders) cannot be loaded with Class.forName using the thread-context classloader. The configured class name does not exist on the classpath, and the original ClassNotFoundException is wrapped into a RuntimeException.

Source

Thrown at extensions/resteasy-reactive/rest-client/runtime/src/main/java/io/quarkus/rest/client/reactive/runtime/RestClientCDIDelegateBuilder.java:397

    private void configureProviders(QuarkusRestClientBuilder builder) {
        Optional<String> maybeProviders = oneOf(restClientConfig.providers(), configRoot.providers());
        if (maybeProviders.isPresent()) {
            registerProviders(builder, maybeProviders.get());
        }
    }

    private void registerProviders(QuarkusRestClientBuilder builder, String providersAsString) {
        for (String s : providersAsString.split(",")) {
            builder.register(providerClassForName(s.trim()));
        }
    }

    private Class<?> providerClassForName(String name) {
        try {
            return Class.forName(name, true, Thread.currentThread().getContextClassLoader());
        } catch (ClassNotFoundException e) {
            throw new RuntimeException("Could not find provider class: " + name);
        }
    }

    private void configureTimeouts(QuarkusRestClientBuilder builder) {
        Long connectTimeout = restClientConfig.connectTimeout().orElse(this.configRoot.connectTimeout());
        if (connectTimeout != null) {
            builder.connectTimeout(connectTimeout, TimeUnit.MILLISECONDS);
        }

        Long readTimeout = restClientConfig.readTimeout().orElse(this.configRoot.readTimeout());
        if (readTimeout != null) {
            builder.readTimeout(readTimeout, TimeUnit.MILLISECONDS);
        }
    }

    private void configureBaseUrl(QuarkusRestClientBuilder builder) {
        Optional<String> propertyOptional = oneOf(restClientConfig.uriReload(), restClientConfig.urlReload());
        if (((baseUriFromAnnotation == null) || baseUriFromAnnotation.isEmpty())

View on GitHub (pinned to e1c734241f)

Solutions

  1. Check the providers config value and correct the fully-qualified class name (verify with an import in code or the jar's contents)
  2. Add the dependency that contains the provider class to the application (verify with mvn dependency:tree and by locating the class in the jar)
  3. If the provider was removed/renamed in an upgrade, replace it with the new class or drop it from the list
  4. Prefer @RegisterProvider(MyProvider.class) on the interface over string-based config so typos fail at compile time

Example fix

// before (application.properties)
quarkus.rest-client.myservice.providers=com.example.auth.AuthFilter
// after (class moved packages)
quarkus.rest-client.myservice.providers=com.example.rest.AuthFilter
Defensive patterns

Strategy: validation

Validate before calling

String providers = "com.example.MyFilter";
Class.forName(providers, true, Thread.currentThread().getContextClassLoader()); // throws ClassNotFoundException early if missing

Try / catch

try {
    MyClient client = Arc.container().instance(MyClient.class).get();
} catch (RuntimeException e) {
    if (e.getMessage() != null && e.getMessage().startsWith("Could not find provider class")) {
        throw new ConfigurationException("Provider class missing from classpath — fix providers config or add dependency", e);
    }
    throw e;
}

Prevention

When it happens

Trigger: A provider class name set via quarkus.rest-client.<key>.providers (or @RegisterProvider / MP Rest Client 'providers' property) references a class that is not on the runtime classpath, or is misspelled / uses the wrong fully-qualified name (e.g. missing package or old package after a library upgrade).

Common situations: Registering a provider like org.example.MyFilter without adding the module/jar providing it to dependencies; renaming or moving the provider class and forgetting to update the config property; upgrading a library whose provider FQN changed; typos in the comma-separated providers list.

Related errors

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/b237e052bb41f6eb. Report an issue: GitHub.