quarkusio/quarkus · error · IllegalStateException

Attempted to load vetoed class '

Error message

Attempted to load vetoed class '

What it means

ClassLoaderLimiter.loadClass vetoes class loads: if the class name is in vetoedClasses, this IllegalStateException is thrown, failing the load request. It lets tests assert that a given class is never loaded by the monitored classloader.

Source

Thrown at independent-projects/bootstrap/core/src/main/java/io/quarkus/bootstrap/classloading/ClassLoaderLimiter.java:71

        }
        if (resourceName.endsWith(".class")) {
            //Skip further tracking on classes as it would create unnecessary noise
            return;
        }
        final String previousLoad = allResourcesLoaded.put(resourceName, classLoaderName);
        if (previousLoad != null) {
            //This diagnostic has no flag, as it's generally useful, doesn't throw exceptions, and should
            //generally not log much at all.
            System.out.println(
                    "Resource loaded multiple times: " + resourceName + ". Currently being loaded by " + classLoaderName +
                            ", previous loaded by " + previousLoad);
        }
    }

    @Override
    public void loadClass(String className, String classLoaderName) {
        if (vetoedClasses.contains(className)) {
            throw new IllegalStateException(
                    "Attempted to load vetoed class '" + className + "' from classloader " + classLoaderName);
        } else if (vetoedRuntimeClasses.contains(className) && classLoaderName.toLowerCase(Locale.ROOT).contains("runtime")) {
            throw new IllegalStateException(
                    "Attempted to load vetoed class '" + className + "' from classloader " + classLoaderName);
        }
    }

    public static Builder builder() {
        return new Builder();
    }

    public static class Builder {
        private final Set<String> vetoedResources = new TreeSet<>();
        private final Set<String> vetoedClasses = new TreeSet<>();
        private final Set<String> vetoedRuntimeClasses = new TreeSet<>();
        private final Set<String> atMostOnceResources = new TreeSet<>();
        private final Set<String> onHitPrintStacktrace = new TreeSet<>();
        private boolean traceAllResourceLoad = false;

View on GitHub (pinned to e1c734241f)

Solutions

1. Remove the code reference that causes the vetoed class to load (use the stack trace to find it).
2. If the class must be loaded, remove the class from the limiter's veto list configuration.
3. Introduce indirection/reflection or move the dependent code to a classloader where the class is allowed.

Example fix

// before
import io.quarkus.deployment.util.ServiceUtil; // deployment class in runtime code -> vetoed
// after
// move the logic to deployment module or avoid the runtime-module import

try { loadAndUse(className); } catch (IllegalStateException e) { if (e.getMessage().startsWith("Attempted to load vetoed class")) { reportLeak(className, e); } else { throw e; } }

When it happens

Trigger: A QuarkusClassLoader attempts to load a class whose name was registered via the limiter's vetoed-class configuration and loadClass is invoked for it.

Common situations: Quarkus tests asserting that e.g. deployment or dev-mode-only classes never leak into runtime classloaders; a regression introduces a reference that triggers loading of the forbidden class.

Related errors

• Attempted to load vetoed resource '
• Resource being loaded more than once:
• resource listed multiple times as never loaded:
• Failed to load steps from %s
• The class (${name}) cannot be created during deployment.

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/3ebfcfa763584d3c. Report an issue: GitHub.