apache/dubbo · error · IllegalStateException

Extension name is blank (Extension ${type})!

Error message

Extension name is blank (Extension ${type})!

What it means

Thrown by ExtensionLoader.addExtension(String name, Class<?> clazz) when the class is not annotated @Adaptive and the name argument is null or blank. Non-adaptive extensions require a unique non-blank name so they can be looked up by name later. Only adaptive classes (annotated @Adaptive) can be registered with a null name.

Source

Thrown at dubbo-common/src/main/java/org/apache/dubbo/common/extension/ExtensionLoader.java:662

     *
     * @param name  extension name
     * @param clazz extension class
     * @throws IllegalStateException when extension with the same name has already been registered.
     */
    public void addExtension(String name, Class<?> clazz) {
        checkDestroyed();
        getExtensionClasses(); // load classes

        if (!type.isAssignableFrom(clazz)) {
            throw new IllegalStateException("Input type " + clazz + " doesn't implement the Extension " + type);
        }
        if (clazz.isInterface()) {
            throw new IllegalStateException("Input type " + clazz + " can't be interface!");
        }

        if (!clazz.isAnnotationPresent(Adaptive.class)) {
            if (StringUtils.isBlank(name)) {
                throw new IllegalStateException("Extension name is blank (Extension " + type + ")!");
            }
            if (cachedClasses.get().containsKey(name)) {
                throw new IllegalStateException("Extension name " + name + " already exists (Extension " + type + ")!");
            }

            cachedNames.put(clazz, name);
            cachedClasses.get().put(name, clazz);
        } else {
            if (cachedAdaptiveClass != null) {
                throw new IllegalStateException("Adaptive Extension already exists (Extension " + type + ")!");
            }

            cachedAdaptiveClass = clazz;
        }
    }

    /**
     * Replace the existing extension via API

View on GitHub (pinned to 3a3043227f)

Solutions

1. Provide a non-blank, unique name as the first argument to addExtension.
2. If the name is computed dynamically, validate it is non-blank before calling addExtension.
3. If registering an adaptive class, ensure it is annotated with @Adaptive.

Example fix

// before
loader.addExtension(null, MyImpl.class);

// after
loader.addExtension("myImpl", MyImpl.class);

if (!clazz.isAnnotationPresent(Adaptive.class) && StringUtils.isBlank(name)) {
    throw new IllegalStateException(
        "Extension name required for non-adaptive class " + clazz);
}
loader.addExtension(name, clazz);

When it happens

Trigger: Calling addExtension(null, ConcreteImpl.class) or addExtension(" ", ConcreteImpl.class) where ConcreteImpl is not @Adaptive. The name is what consumers use to select this extension via getExtension(name), so it must be meaningful and non-empty.

Common situations: Developer forgets to specify a name when programmatically registering a test extension. A helper method that wraps addExtension passes a computed name that happens to be null or empty.

Related errors

• Extension name is blank (Extension {})!
• Input type ${clazz} doesn't implement the Extension ${type}
• Input type ${clazz} can't be interface!
• Extension name ${name} already exists (Extension ${type})!
• Adaptive Extension already exists (Extension ${type})!

AI-assisted analysis of apache/dubbo@3a3043227f (2026-08-14). Data as JSON: /api/errors/f3c591d77ee7caaa. Report an issue: GitHub.