alibaba/canal · error · IllegalStateException

more than 1 default extension name on extension {}: {}

Error message

more than 1 default extension name on extension {}: {}

What it means

Error "more than 1 default extension name on extension {}: {}" thrown in alibaba/canal.

Source

Thrown at client-adapter/common/src/main/java/com/alibaba/otter/canal/client/adapter/support/ExtensionLoader.java:256

                                         // the app using Spring Tools Suit play
                                         // button.
            jarPath = jarPath.replaceAll("/classes/.*", "/classes/");
        }
        Path path = Paths.get(jarPath).getParent(); // Paths - from java 8
        if (path != null) {
            return path.toString();
        }
        return null;
    }

    private Map<String, Class<?>> loadExtensionClasses() {
        final SPI defaultAnnotation = type.getAnnotation(SPI.class);
        if (defaultAnnotation != null) {
            String value = defaultAnnotation.value();
            if ((value = value.trim()).length() > 0) {
                String[] names = NAME_SEPARATOR.split(value);
                if (names.length > 1) {
                    throw new IllegalStateException("more than 1 default extension name on extension " + type.getName()
                                                    + ": " + Arrays.toString(names));
                }
                if (names.length == 1) cachedDefaultName = names[0];
            }
        }

        Map<String, Class<?>> extensionClasses = new HashMap<>();

        // 1. plugin folder，customized extension classLoader （jar_dir/plugin）
        String dir = File.separator + this.getJarDirectoryPath() + File.separator + "plugin";

        File externalLibDir = new File(dir);
        if (!externalLibDir.exists()) {
            externalLibDir = new File(File.separator + this.getJarDirectoryPath() + File.separator + "canal-adapter"
                                      + File.separator + "plugin");
        }
        logger.info("extension classpath dir: " + externalLibDir.getAbsolutePath());
        if (externalLibDir.exists()) {

View on GitHub (pinned to 87be50e876)

Solutions

1. Declare only one @SPI default name on the extension interface; remove duplicate default names.
2. Check for duplicated SPI annotations introduced by shading/merging of jars.

When it happens

Trigger: Thrown at client-adapter/common/src/main/java/com/alibaba/otter/canal/client/adapter/support/ExtensionLoader.java:256 when the library encounters an invalid state.

Common situations: Multiple default extensions declared for one SPI. Reject the configuration at load time; exactly one default (or none) must be enforced.

AI-assisted analysis of alibaba/canal@87be50e876 (2026-08-14). Data as JSON: /api/errors/9f67adcd78c74b32. Report an issue: GitHub.