quarkusio/quarkus · error · ClassLoaderLimiterConsistencyException

resource listed multiple times as loaded at most once:

Error message

resource listed multiple times as loaded at most once: 

What it means

Thrown by ClassLoaderLimiter.Builder.loadedAtMostOnceResource when the same resource name is registered twice as loaded-at-most-once. The limiter tracks these resources to assert each is loaded zero or one times, so duplicates would corrupt that assertion. It is a misuse of the builder API at bootstrap time.

Source

Thrown at independent-projects/bootstrap/core/src/main/java/io/quarkus/bootstrap/classloading/ClassLoaderLimiter.java:188

         * Useful to check that a resource is being loaded only once, or never.
         * If there is an attempt of loading the matched resource more than once, a runtime exception will be thrown instead:
         * useful for running integration tests to verify your assumptions.
         * <p>
         * Limitations: if the resource is being loaded using the bootstrap classloader we
         * can't check it; some frameworks explicitly request using the base classloader
         * for resource loading (or even use the Filesystem API), so they can't be tested via this method.
         * Additionally, some frameworks will load the same resource but in different Quarkus build
         * phases (which map to different classloaders); such cases will count as multiple times
         * so it might not be suited to test this way.
         *
         * @param resourceFullName the resource name
         * @return this, for method chaining.
         */
        public Builder loadedAtMostOnceResource(String resourceFullName) {
            Objects.requireNonNull(resourceFullName);
            final boolean add = atMostOnceResources.add(resourceFullName);
            if (!add)
                throw new ClassLoaderLimiterConsistencyException(
                        "resource listed multiple times as loaded at most once: " + resourceFullName);
            if (vetoedResources.contains(resourceFullName)) {
                throw new ClassLoaderLimiterConsistencyException(
                        resourceFullName + " is being listed both as never loaded and as at most once");
            }
            return this;
        }

        /**
         * When the specified resource is loaded, print a full stack trace on System out.
         * This is not useful for testing, but handy to trace were a certain load is coming from,
         * should you need to diagnose a failing expectation.
         *
         * @param resourceFullName
         * @return this, for method chaining.
         */
        public Builder produceStackTraceOnLoad(String resourceFullName) {
            Objects.requireNonNull(resourceFullName);

View on GitHub (pinned to e1c734241f)

Solutions

1. Deduplicate resource names before calling the builder
2. Remove one of the duplicate registrations
3. Keep ownership of at-most-once registration in a single component

Example fix

// before
builder.loadedAtMostOnceResource("META-INF/services/com.foo.Service");
builder.loadedAtMostOnceResource("META-INF/services/com.foo.Service"); // throws
// after
if (resourcesSeen.add("META-INF/services/com.foo.Service")) builder.loadedAtMostOnceResource("META-INF/services/com.foo.Service");

if (!atMostOnceSeen.add(name)) { /* skip */ }

When it happens

Trigger: Calling builder.loadedAtMostOnceResource(name) twice for the same resourceFullName (Set.add returns false).

Common situations: Two integrations or generated code paths both marking the same resource (e.g. a service file) as at-most-once.

Related errors

• is being listed both as never loaded and as at most once
• never loaded class listed multiple times:
• resource listed multiple times to produce a stacktrace:
• Invalid URL:
• Failed to load steps from %s

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/a7b6b43a47ac399d. Report an issue: GitHub.