apache/seatunnel · error · RuntimeException

Unsupported classloader:

Error message

Unsupported classloader: 

What it means

ConfigValidationUtils installs an ADD_URL_TO_CLASSLOADER consumer that reflectively calls URLClassLoader.addURL to inject plugin jars. If the classloader is not a URLClassLoader (or the reflective add fails), it wraps the failure in RuntimeException('Unsupported classloader: <className>').

Solutions

1. Ensure validation runs with a URLClassLoader as the context classloader
2. Wrap the target classloader in a new URLClassLoader(urls, parent) before validation
3. Check the exception cause; if the reflective addURL itself failed, align JDK version/permissions

Example fix

// before
ClassLoader cl = Thread.currentThread().getContextClassLoader(); // custom loader
// after
ClassLoader parent = Thread.currentThread().getContextClassLoader();
URLClassLoader cl = new URLClassLoader(urls, parent); // ensure URLClassLoader is used

if (!(Thread.currentThread().getContextClassLoader() instanceof URLClassLoader)) { /* wrap in new URLClassLoader(urls, parent) */ }

boolean isUrlClassLoader(ClassLoader cl) { return cl instanceof URLClassLoader; }

try { ConfigValidationUtils.validate(config); } catch (RuntimeException e) { if (e.getMessage().startsWith("Unsupported classloader")) { /* re-run with URLClassLoader */ } }

When it happens

Trigger: Plugin discovery runs with a classloader that is not a URLClassLoader, e.g. when running inside a container/agent that supplies a custom (AppCDS, Spring Boot LaunchedURLClassLoader variants, module) classloader.

Common situations: Embedding SeaTunnel validation in another application server, unusual -Djava.system.class.loader settings, or running under tooling that replaces the context classloader.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• Unsupported classloader
• can't load jar use current thread classloader, use…
• CONFIG_VALIDATION_FAILED
• CREATE_DRIVER_FAILED
• Failed to call factoryIdentifier method.

AI-assisted analysis of apache/seatunnel@cf67b549a7 (2026-09-10). Data as JSON: /api/errors/1afbfe8d74391015. Report an issue: GitHub.

Appendix: source

Thrown at seatunnel-core/seatunnel-core-starter/src/main/java/org/apache/seatunnel/core/starter/utils/ConfigValidationUtils.java:101

    private static final BiConsumer<ClassLoader, List<URL>> ADD_URL_TO_CLASSLOADER =
            (classLoader, urls) -> {
                if (classLoader instanceof URLClassLoader) {
                    urls.forEach(url -> ReflectionUtils.invoke(classLoader, "addURL", url));
                } else {
                    try {
                        Optional<Method> method =
                                ReflectionUtils.getDeclaredMethod(
                                        URLClassLoader.class, "addURL", URL.class);
                        if (!method.isPresent()) {
                            throw new IllegalStateException(
                                    "Unable to find addURL method from URLClassLoader");
                        }
                        method.get().setAccessible(true);
                        for (URL url : urls) {
                            method.get().invoke(classLoader, url);
                        }
                    } catch (Exception e) {
                        throw new RuntimeException(
                                "Unsupported classloader: " + classLoader.getClass().getName(), e);
                    }
                }
            };

    private ConfigValidationUtils() {}

    public static void validate(Config config) {
        validate(config, CheckResult.success());
    }

    public static void validate(Config config, CheckResult checkResult) {
        if (!checkResult.isSuccess()) {
            throw new ConfigCheckException(checkResult.getMsg());
        }

        ClassLoader parentClassLoader = Thread.currentThread().getContextClassLoader();
        ClassLoader validationClassLoader = prepareClassLoader(config, parentClassLoader);

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