apache/maven · error · DIException

Error while discovering DI classes from classLoader

Error message

Error while discovering DI classes from classLoader

What it means

Injector.discover(ClassLoader) scans every META-INF/maven/org.apache.maven.api.di.Inject resource — files the DI annotation processor generates to list classes for implicit binding — loads each listed class, and binds it. Any failure while enumerating resources, reading a file, or loading/binding a listed class is wrapped in DIException 'Error while discovering DI classes from classLoader'.

Source

Thrown at impl/maven-di/src/main/java/org/apache/maven/di/impl/InjectorImpl.java:114

            while (enumeration.hasMoreElements()) {
                URL url = enumeration.nextElement();
                if (loadedUrls.add(url.toExternalForm())) {
                    try (InputStream is = url.openStream();
                            BufferedReader reader =
                                    new BufferedReader(new InputStreamReader(Objects.requireNonNull(is)))) {
                        for (String line : reader.lines()
                                .map(String::trim)
                                .filter(l -> !l.isEmpty())
                                .filter(l -> !l.startsWith("#"))
                                .toList()) {
                            Class<?> clazz = classLoader.loadClass(line);
                            bindImplicit(clazz);
                        }
                    }
                }
            }
        } catch (Exception e) {
            throw new DIException("Error while discovering DI classes from classLoader", e);
        }
        return this;
    }

    @Nonnull
    @Override
    public Injector bindScope(@Nonnull Class<? extends Annotation> scopeAnnotation, @Nonnull Scope scope) {
        return bindScope(scopeAnnotation, () -> scope);
    }

    @Nonnull
    @Override
    public Injector bindScope(@Nonnull Class<? extends Annotation> scopeAnnotation, @Nonnull Supplier<Scope> scope) {
        if (scopes.put(scopeAnnotation, scope) != null) {
            throw new DIException(
                    "Cannot rebind scope annotation class to a different implementation: " + scopeAnnotation);
        }
        return this;

View on GitHub (pinned to e4093d4e12)

Solutions

1. Clean-build so the annotation processor regenerates META-INF/maven/org.apache.maven.api.di.Inject (mvn clean install)
2. Configure shading to append/merge these descriptor files instead of overwriting them
3. Read the DIException cause: ClassNotFoundException names the exact missing class — fix or remove that entry's source module
4. Ensure the classloader passed to discover() is the one that actually contains the listed classes

Example fix

<!-- before: maven-shade-plugin overwrites the descriptor -->
<!-- after: append entries from merged jars -->
<transformer implementation="org.apache.maven.plugins.shade.resource.AppendingTransformer">
  <resource>META-INF/maven/org.apache.maven.api.di.Inject</resource>
</transformer>

try {
    injector.discover(classLoader);
} catch (DIException e) {
    Throwable cause = e.getCause();
    if (cause instanceof ClassNotFoundException cnfe) {
        // stale META-INF/maven/org.apache.maven.api.di.Inject entry: clean and rebuild
        log.error("stale DI descriptor lists {}", cnfe.getMessage(), e);
    }
    throw e;
}

When it happens

Trigger: discover() hitting a resource that lists a class name which no longer exists (ClassNotFoundException), an unreadable or corrupt resource (IOException), or a listed class whose binding fails.

Common situations: Stale annotation-processor output after incremental compilation or refactors; shaded or merged jars where the descriptor file was overwritten instead of concatenated; classes listed in a different classloader layer (JPMS or isolating loaders).

Related errors

• A required class was missing while executing {}: {}
• A type incompatibility occurred while executing ${mojoDescri
• Could not determine current Maven version
• Expected type from key {} to be parameterized
• Error while initializing binding {}

AI-assisted analysis of apache/maven@e4093d4e12 (2026-08-21). Data as JSON: /api/errors/872805f6271002a4. Report an issue: GitHub.