quarkusio/quarkus · error · RuntimeException

Failed to instantiate hostname verifier class " + verifier +

Error message

Failed to instantiate hostname verifier class " + verifier + ". Make sure it has a public, no-argument constructor

What it means

After loading and constructing the configured hostname verifier, registerHostnameVerifier casts it to jakarta/javax.net.ssl.HostnameVerifier. If instantiation or access fails (InstantiationException, IllegalAccessException, InvocationTargetException — e.g. the constructor is non-public or throws), the exception is wrapped in this RuntimeException with guidance to provide a public no-arg constructor.

Source

Thrown at extensions/resteasy-reactive/rest-client/runtime/src/main/java/io/quarkus/rest/client/reactive/runtime/RestClientCDIDelegateBuilder.java:296

        Optional<String> maybeHostnameVerifier = oneOf(restClientConfig.hostnameVerifier(), configRoot.hostnameVerifier());
        if (maybeHostnameVerifier.isPresent()) {
            registerHostnameVerifier(maybeHostnameVerifier.get(), builder);
        }

        oneOf(restClientConfig.verifyHost(), configRoot.verifyHost()).ifPresent(builder::verifyHost);
    }

    private void registerHostnameVerifier(String verifier, QuarkusRestClientBuilder builder) {
        try {
            Class<?> verifierClass = Thread.currentThread().getContextClassLoader().loadClass(verifier);
            builder.hostnameVerifier((HostnameVerifier) verifierClass.getDeclaredConstructor().newInstance());
        } catch (NoSuchMethodException e) {
            throw new RuntimeException(
                    "Could not find a public, no-argument constructor for the hostname verifier class " + verifier, e);
        } catch (ClassNotFoundException e) {
            throw new RuntimeException("Could not find hostname verifier class " + verifier, e);
        } catch (InstantiationException | IllegalAccessException | InvocationTargetException e) {
            throw new RuntimeException(
                    "Failed to instantiate hostname verifier class " + verifier
                            + ". Make sure it has a public, no-argument constructor",
                    e);
        } catch (ClassCastException e) {
            throw new RuntimeException("The provided hostname verifier " + verifier + " is not an instance of HostnameVerifier",
                    e);
        }
    }

    private void registerKeyStore(String keyStorePath, QuarkusRestClientBuilder builder) {
        Optional<String> keyStorePassword = oneOf(restClientConfig.keyStorePassword(), configRoot.keyStorePassword());
        Optional<String> keyStoreType = oneOf(restClientConfig.keyStoreType(), configRoot.keyStoreType());

        try {
            KeyStore keyStore = KeyStore.getInstance(keyStoreType.orElse("JKS"));
            if (keyStorePassword.isEmpty()) {
                throw new IllegalArgumentException("No password provided for keystore");
            }

View on GitHub (pinned to e1c734241f)

Solutions

1. Make the class and its no-arg constructor public and the class static (if nested).
2. Fix or remove initialization logic in the constructor that throws.
3. If parameters are needed, register the verifier programmatically through the builder rather than via configuration.

Example fix

// before
class MyVerifier implements HostnameVerifier { ... } // package-private

// after
public class MyVerifier implements HostnameVerifier {
    public MyVerifier() { }
    ...
}

Class<?> c = Class.forName("com.example.MyVerifier");
if (java.lang.reflect.Modifier.isAbstract(c.getModifiers()) || !java.lang.reflect.Modifier.isPublic(c.getModifiers())) {
    throw new IllegalStateException("Verifier must be public and concrete");
}

boolean publiclyInstantiable(Class<?> c) {
    return java.lang.reflect.Modifier.isPublic(c.getModifiers())
        && !java.lang.reflect.Modifier.isAbstract(c.getModifiers())
        && hasPublicNoArgCtor(c);
}

try {
    // build client with configured verifier
} catch (RuntimeException e) {
    if (e.getMessage() != null && e.getMessage().contains("Failed to instantiate hostname verifier")) {
        builder.hostnameVerifier(new DefaultVerifier());
    } else throw e;
}

When it happens

Trigger: Configured hostname-verifier class has a non-public no-arg constructor (InstantiationException/IllegalAccessException) or its constructor throws an exception during initialization.

Common situations: Package-private verifier class; constructor performing initialization that fails (throws IllegalStateException from within); inner (non-static) classes being instantiated reflectively.

Related errors

• Could not find a public, no-argument constructor for the hos
• Could not find hostname verifier class " + verifier
• The provided hostname verifier " + verifier + " is not an in
• No password provided for keystore
• Failed to initialize trust store from classpath resource " +

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/992f4dc41f35a423. Report an issue: GitHub.