alibaba/ARouter · error · HandlerException

Extract the default group failed! There's nothing between 2

Error message

Extract the default group failed! There's nothing between 2 '/'!

What it means

When the path starts with '/' but has no second '/' (or nothing between the two slashes), extractGroup cannot produce a group name. The code attempts substring extraction and throws HandlerException for the empty-group case; note the surrounding catch logs a warning and returns null for other parse failures, which then triggers the 'Parameter is invalid' error in build(path, group, ...).

Source

Thrown at arouter-api/src/main/java/com/alibaba/android/arouter/launcher/_ARouter.java:251

        } catch (HandlerException invalidPath) {
            return false;
        }

        return LogisticsCenter.hasRoute(postcard);
    }

    /**
     * Extract the default group from path.
     */
    private String extractGroup(String path) {
        if (TextUtils.isEmpty(path) || !path.startsWith("/")) {
            throw new HandlerException(Consts.TAG + "Extract the default group failed, the path must be start with '/' and contain more than 2 '/'!");
        }

        try {
            String defaultGroup = path.substring(1, path.indexOf("/", 1));
            if (TextUtils.isEmpty(defaultGroup)) {
                throw new HandlerException(Consts.TAG + "Extract the default group failed! There's nothing between 2 '/'!");
            } else {
                return defaultGroup;
            }
        } catch (Exception e) {
            logger.warning(Consts.TAG, "Failed to extract default group! " + e.getMessage());
            return null;
        }
    }

    static void afterInit() {
        // Trigger interceptor init, use byName.
        interceptorService = (InterceptorService) ARouter.getInstance().build("/arouter/service/interceptor").navigation();
    }

    protected <T> T navigation(Class<? extends T> service) {
        try {
            Postcard postcard = LogisticsCenter.buildProvider(service.getName());

View on GitHub (pinned to 84f451d244)

Solutions

1. Use two-segment paths: '/group/name' (e.g. '/app/main' instead of '/main')
2. Re-register the @Route(path) annotations with a proper group segment
3. Add a path normalizer (PathReplaceService) that inserts a default group for single-segment paths
4. Check for accidental double slashes in configured paths

Example fix

// before
@Route(path = "/main")            // no group segment
public class MainActivity ...
// after
@Route(path = "/app/main")        // group 'app', path 'main'
public class MainActivity ...

public static boolean hasGroupSegment(String path) {
    if (path == null || !path.startsWith("/")) return false;
    int second = path.indexOf('/', 1);
    return second > 1; // non-empty group between slashes
}

try {
    ARouter.getInstance().build(path).navigation();
} catch (HandlerException e) {
    Log.w(TAG, "Path missing group segment", e);
}

When it happens

Trigger: Calling build("/login") — starts with '/' but no second segment — or build("//detail") with nothing between the slashes.

Common situations: Paths registered without a group prefix; single-segment paths like "/main"; migrating from another router library that allowed single-segment paths.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

Related errors

• Extract the default group failed, the path must be start wit
• ARouter::Init::Invoke init(context) first!
• ARouterCore::Init::Invoke init(context) first!
• Parameter is invalid!
• Parameter invalid!

AI-assisted analysis of alibaba/ARouter@84f451d244 (2026-09-06). Data as JSON: /api/errors/3108b8b0ed3c4e48. Report an issue: GitHub.