alibaba/canal · error · IllegalArgumentException

Extension type({}) is not interface!

Error message

Extension type({}) is not interface!

What it means

Error "Extension type({}) is not interface!" thrown in alibaba/canal.

Source

Thrown at client-adapter/common/src/main/java/com/alibaba/otter/canal/client/adapter/support/ExtensionLoader.java:76

    private final ConcurrentMap<String, Holder<Object>>              cachedInstances            = new ConcurrentHashMap<>();

    private String                                                   cachedDefaultName;

    private ConcurrentHashMap<String, IllegalStateException>         exceptions                 = new ConcurrentHashMap<>();

    private static <T> boolean withExtensionAnnotation(Class<T> type) {
        return type.isAnnotationPresent(SPI.class);
    }

    public static <T> ExtensionLoader<T> getExtensionLoader(Class<T> type) {
        return getExtensionLoader(type, DEFAULT_CLASSLOADER_POLICY);
    }

    @SuppressWarnings("unchecked")
    public static <T> ExtensionLoader<T> getExtensionLoader(Class<T> type, String classLoaderPolicy) {
        if (type == null) throw new IllegalArgumentException("Extension type == null");
        if (!type.isInterface()) {
            throw new IllegalArgumentException("Extension type(" + type + ") is not interface!");
        }
        if (!withExtensionAnnotation(type)) {
            throw new IllegalArgumentException("Extension type(" + type + ") is not extension, because WITHOUT @"
                                               + SPI.class.getSimpleName() + " Annotation!");
        }

        ExtensionLoader<T> loader = (ExtensionLoader<T>) EXTENSION_LOADERS.get(type);
        if (loader == null) {
            EXTENSION_LOADERS.putIfAbsent(type, new ExtensionLoader<T>(type, classLoaderPolicy));
            loader = (ExtensionLoader<T>) EXTENSION_LOADERS.get(type);
        }
        return loader;
    }

    private ExtensionLoader(Class<?> type, String classLoaderPolicy){
        this.type = type;
        this.classLoaderPolicy = classLoaderPolicy;
    }

View on GitHub (pinned to 87be50e876)

Solutions

1. Only interface types can be used as extension points; change the type argument to an interface.
2. Refactor the extension point into an interface if it is currently a concrete/abstract class.

When it happens

Trigger: Thrown at client-adapter/common/src/main/java/com/alibaba/otter/canal/client/adapter/support/ExtensionLoader.java:76 when the library encounters an invalid state.

Common situations: SPI type is not an interface. Enforce the interface contract at load time; concrete classes cannot be extension points.

AI-assisted analysis of alibaba/canal@87be50e876 (2026-08-14). Data as JSON: /api/errors/7e46c8b9837b31ea. Report an issue: GitHub.