quarkusio/quarkus · error · UncheckedIOException

class reading failed

Error message

 class reading failed

What it means

removePropertiesWithCandidateAnalysis loads a compiled @ConfigurationProperties class as a resource from the application index and parses it with ASM's ClassReader. If the class resource cannot be read (null stream or I/O failure), the IOException is wrapped in an UncheckedIOException with '<class> class reading failed', aborting the build.

Source

Thrown at extensions/spring-boot-properties/deployment/src/main/java/io/quarkus/spring/boot/properties/deployment/ConfigPropertyBuildItemCandidateUtil.java:36

public class ConfigPropertyBuildItemCandidateUtil {

    private static final Logger LOGGER = Logger.getLogger(ConfigPropertyBuildItemCandidateUtil.class);

    /**
     * This method inspects the {@code configClass} bytecode to identify all fields that have a default value set in the class
     * constructor. These fields are removed from the {@link ConfigPropertyBuildItemCandidate} list because we don't want to
     * throw an exception if no config property value was provided for them. There is no bytecode modification performed during
     * this process.
     */
    public static void removePropertiesWithDefaultValue(ClassLoader classLoader, String configClass,
            List<ConfigPropertyBuildItemCandidate> candidates) {
        final String resourceName = fromClassNameToResourceName(configClass);
        try (InputStream is = classLoader.getResourceAsStream(resourceName)) {
            ClassReader configClassReader = new ClassReader(is);
            configClassReader.accept(new ConfigClassVisitor(candidates, configClass), 0);
        } catch (IOException e) {
            throw new UncheckedIOException(configClass + " class reading failed", e);
        }
    }

    private static class ConfigClassVisitor extends ClassVisitor {

        private final List<ConfigPropertyBuildItemCandidate> candidates;
        private final String configClass;

        private ConfigClassVisitor(List<ConfigPropertyBuildItemCandidate> candidates, String configClass) {
            super(Gizmo.ASM_API_VERSION);
            this.candidates = candidates;
            this.configClass = configClass;
        }

        @Override
        public MethodVisitor visitMethod(int access, String name, String descriptor, String signature, String[] exceptions) {
            MethodVisitor superMethodVisitor = super.visitMethod(access, name, descriptor, signature, exceptions);
            if (name.equals("<init>") && descriptor.equals("()V")) {

View on GitHub (pinned to e1c734241f)

Solutions

1. Run a clean build (./mvnw clean install) to restore the missing or stale class file in the target output.
2. Verify the @ConfigurationProperties class exists at the FQCN the annotation references and is compiled into the module on the classpath.
3. Check build/packaging excludes or shade/relocation config that might strip the .class resource.
4. Inspect the cause chain of the UncheckedIOException for the underlying IOException details.

// build script: clean rebuild on this failure
try {
  ./mvnw install -f extensions/spring-boot-properties/
} catch (UncheckedIOException e) if (e.message.endsWith("class reading failed")) {
  ./mvnw clean install  // rebuild to regenerate the missing/corrupt class resource
}

When it happens

Trigger: The config class name passed to removePropertiesWithDefaultValue cannot be resolved to a class-file resource by the given ClassLoader (getResourceAsStream returns null, making ClassReader throw a null-stream IOException), or the class file is unreadable/corrupt — raised while filtering config property build item candidates.

Common situations: The class is generated or transformed so its .class resource isn't on the deployment-time classpath; a stale incremental build where the class file was deleted; packaging that excludes class resources; class-name/package mismatch after refactoring.

Related errors

• Failed to open path tree with root %s
• The class (${className}) cannot be found during deployment.
• ${className} class reading failed
• Failed to load CodeGenProvider class from deployment classlo
• Failed to read %s

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/52026a89a8e82d5c. Report an issue: GitHub.