quarkusio/quarkus · error · RuntimeException

Could not find hostname verifier class ${verifier}

Error message

Could not find hostname verifier class ${verifier}

What it means

The hostname verifier class name configured for a REST client could not be loaded through the thread context class loader (ClassNotFoundException). The value must be a fully qualified class name visible to the application at runtime. This typically means the class name is wrong or the class is not on the classpath/native image.

Source

Thrown at extensions/resteasy-classic/resteasy-client/runtime/src/main/java/io/quarkus/restclient/runtime/RestClientBase.java:159

            registerHostnameVerifier(hostnameVerifier.get(), builder);
        } else {
            // If `verify-host` is disabled, we configure the client using the `NoopHostnameVerifier` verifier.
            Optional<Boolean> verifyHost = oneOf(restClientConfig.verifyHost(), configRoot.verifyHost());
            if (verifyHost.isPresent() && !verifyHost.get()) {
                registerHostnameVerifier(NoopHostnameVerifier.class.getName(), builder);
            }
        }
    }

    private void registerHostnameVerifier(String verifier, RestClientBuilder 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, RestClientBuilder builder) {
        try {
            Optional<String> keyStoreType = oneOf(restClientConfig.keyStoreType(), configRoot.keyStoreType());
            KeyStore keyStore = KeyStore.getInstance(keyStoreType.orElse("JKS"));

            Optional<String> keyStorePassword = oneOf(restClientConfig.keyStorePassword(), configRoot.keyStorePassword());
            if (keyStorePassword.isEmpty()) {

View on GitHub (pinned to e1c734241f)

Solutions

1. Verify the configured value is the exact fully-qualified class name (package included, correct case)
2. Add the module/jar containing the class to the application dependencies
3. Check that the class wasn't renamed or moved; update the config accordingly

Example fix

# before
quarkus.rest-client.my-client.hostname-verifier=com.acme.MyHostVerifier
# after
quarkus.rest-client.my-client.hostname-verifier=com.acme.security.MyHostnameVerifier

try {
    Class.forName(verifierName, false, Thread.currentThread().getContextClassLoader());
} catch (ClassNotFoundException e) {
    throw new IllegalStateException("Hostname verifier class not on classpath: " + verifierName);
}

try {
    // build the rest client / start the app
} catch (RuntimeException e) {
    if (e.getCause() instanceof ClassNotFoundException) {
        log.error("Check hostname-verifier config value and app dependencies");
    }
}

When it happens

Trigger: Setting quarkus.rest-client.<name>.hostname-verifier (or matching MicroProfile config) to a misspelled or non-existent fully-qualified class name, or a class in a module/jar not included in the application.

Common situations: Typos or wrong package in the configured class name; class lives in a library not declared as a dependency; native-image build excluded the class (no reflection/registration needed for load, but the class itself must be reachable); renaming/refactoring the class without updating config.

Related errors

• Could not find a public, no-argument constructor for the hos
• Failed to instantiate hostname verifier class ${verifier}. M
• The provided hostname verifier ${verifier} is not an instanc
• No password provided for keystore
• Failed to initialize trust store from classpath resource ${k

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/82a3c8edd5caa706. Report an issue: GitHub.