What causes "Unable to lookup Mojo" in apache/maven?

Unwrap the cause chain - the nested exception is the real reason (missing binding, constructor exception, hint mismatch).

apache/maven · error · PluginContainerException

Unable to lookup Mojo

Error message

Unable to lookup Mojo

What it means

While loading a Maven-4-style mojo, the Sisu injector's getInstance call on the implementation class (keyed with the descriptor's role hint) threw: the mojo class could not be instantiated - constructor failure, missing binding for an injected parameter, or a hint/annotation mismatch. Any such failure is wrapped in PluginContainerException 'Unable to lookup Mojo'.

Source

Thrown at impl/maven-core/src/main/java/org/apache/maven/plugin/internal/DefaultMavenPluginManager.java:576

                LoggerFactory.getLogger(mojoExecution.getMojoDescriptor().getFullGoalName()));
        try {
            Injector injector = Injector.create();
            injector.discover(pluginRealm);
            // Add known classes
            // TODO: get those from the existing plexus scopes ?
            injector.bindInstance(Session.class, sessionV4);
            injector.bindInstance(Project.class, project);
            injector.bindInstance(org.apache.maven.api.MojoExecution.class, execution);
            injector.bindInstance(org.apache.maven.api.plugin.Log.class, log);

            Map<Class<? extends Service>, Supplier<? extends Service>> services = sessionV4.getAllServices();
            services.forEach((itf, svc) -> injector.bindSupplier((Class<Service>) itf, (Supplier<Service>) svc));

            mojo = mojoInterface.cast(injector.getInstance(
                    Key.of(mojoDescriptor.getImplementationClass(), mojoDescriptor.getRoleHint())));

        } catch (Exception e) {
            throw new PluginContainerException(mojoDescriptor, pluginRealm, "Unable to lookup Mojo", e);
        }

        XmlNode dom = mojoExecution.getConfiguration() != null
                ? mojoExecution.getConfiguration().getDom()
                : null;

        PlexusConfiguration pomConfiguration;

        if (dom == null) {
            pomConfiguration = new DefaultPlexusConfiguration("configuration");
        } else {
            pomConfiguration = XmlPlexusConfiguration.toPlexusConfiguration(dom);
        }

        ExpressionEvaluator expressionEvaluator =
                new PluginParameterExpressionEvaluatorV4(sessionV4, project, execution);

        for (MavenPluginConfigurationValidator validator : configurationValidators) {

View on GitHub (pinned to e4093d4e12)

Solutions

Unwrap the cause chain - the nested exception is the real reason (missing binding, constructor exception, hint mismatch).
If the hint mismatched, clean-rebuild the plugin so plugin.xml and @Named agree.
Ensure the mojo class is concrete with an injectable constructor (no-arg or @Inject).
Check that every service injected into the mojo is provided by the realm or by Maven core.

Example fix

// before: plugin.xml role hint is "my-goal" but the class says
@Named("myMojo")
class MyMojo extends AbstractMojo {}
// after: names agree (and rebuild so the descriptor matches)
@Named("my-goal")
class MyMojo extends AbstractMojo {}

Defensive patterns

Strategy: validation

Validate before calling

// run inside the plugin's test suite: fail fast when the mojo cannot be wired
@Test void mojoIsInstantiable() {
    Injector i = Guice.createInjector(
        new WireModule(new ClassSpaceModule(new URLClassSpace(getClass().getClassLoader()))));
    MyMojo mojo = i.getInstance(Key.of(MyMojo.class, "my-goal"));
    assertNotNull(mojo);
}

Try / catch

try {
    mojo = pluginManager.getConfiguredMojo(mojoInterface, session, mojoExecution);
} catch (PluginContainerException e) {
    Throwable root = e;
    while (root.getCause() != null) root = root.getCause();
    // root is the real instantiation failure (binding/constructor/hint): fix the plugin, not the POM
    throw new IllegalStateException("mojo wiring failed: " + root, e);
}

Prevention

Keep maven-plugin-plugin and maven-plugin-annotations versions aligned
Avoid logic in mojo constructors; initialize inside execute()
Run injector smoke tests in plugin CI so lookup failures never reach users

When it happens

Trigger: The mojo constructor or a field initializer throws; the @Named value on the mojo no longer matches the role hint recorded in plugin.xml; a required injected service has no binding in the realm; the descriptor names an abstract class as implementation.

Common situations: Plugin rebuilt without regenerating plugin.xml after renames; descriptors and annotations produced by mismatched maven-plugin-plugin versions; environments missing a service the mojo expects.

Related errors

AI-assisted analysis of apache/maven@e4093d4e12 (2026-08-21). Data as JSON: /api/errors/27c3f6adf5eadbbe. Report an issue: GitHub.