quarkusio/quarkus · error · IllegalStateException

Resource being loaded more than once:

Error message

Resource being loaded more than once: 

What it means

ClassLoaderLimiter tracks resources registered as atMostOnceResources and throws this IllegalStateException the second time any classloader attempts to load them. It is an assertion mechanism that guarantees a resource is opened at most once across all monitored classloaders.

Source

Thrown at independent-projects/bootstrap/core/src/main/java/io/quarkus/bootstrap/classloading/ClassLoaderLimiter.java:50

    @Override
    public void openResourceStream(String resourceName, String classLoaderName) {
        Objects.requireNonNull(resourceName);
        Objects.requireNonNull(classLoaderName);
        if (traceAllResourceLoad) {
            System.out.println("Opening resource: " + resourceName);
        }
        if (onHitPrintStacktrace.contains(resourceName)) {
            final RuntimeException e = new RuntimeException("Tracing load of resource: " + resourceName);
            e.printStackTrace();
        }
        if (vetoedResources.contains(resourceName)) {
            throw new IllegalStateException(
                    "Attempted to load vetoed resource '" + resourceName + "' from classloader " + classLoaderName);
        }
        if (atMostOnceResources.contains(resourceName)) {
            final String previousLoadEvent = atMostOnceResourcesLoaded.put(resourceName, classLoaderName);
            if (previousLoadEvent != null) {
                throw new IllegalStateException("Resource being loaded more than once: " + resourceName + ".\n" +
                        "Attempted load by " + classLoaderName + ", recorded previous load by " + previousLoadEvent);
            }
        }
        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

View on GitHub (pinned to e1c734241f)

Solutions

1. Introduce caching so the resource is read once and reused (e.g. static/holder caching in the loading code).
2. Identify the two loading classloaders from the message and unify the loading path in one of them.
3. If duplicate loads are acceptable now, drop the atMostOnceResource registration from the limiter builder.

Example fix

// before
try (InputStream in = cl.getResourceAsStream("app.properties")) { ... } // called repeatedly
// after
private static final Properties PROPS = loadOnce("app.properties");

// ensure single read: cache resource contents at first access
private static final Map<String, byte[]> CACHE = new ConcurrentHashMap<>();
byte[] data = CACHE.computeIfAbsent(name, n -> readOnce(n));

try { open(path); } catch (IllegalStateException e) { if (e.getMessage().startsWith("Resource being loaded more than once")) { log.error("Duplicate load: {}", e.getMessage()); } else { throw e; } }

When it happens

Trigger: openResourceStream is called for a resource listed in atMostOnceResources that already has a recorded load event in atMostOnceResourcesLoaded (put returns a non-null previous event).

Common situations: Tests verifying single-load invariants for config/bootstrap resources; failures when caching is missing and the same resource is re-read, or when two subsystems independently read the same resource.

Related errors

• Attempted to load vetoed resource '
• Attempted to load vetoed class '
• 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/8a76401224d2eb5e. Report an issue: GitHub.