flowable/flowable-engine · error · IllegalArgumentException

Channel definition <channelDefinition> cannot resolve <resol

Error message

Channel definition <channelDefinition> cannot resolve <resolvedValue> as a String[] or a String or a Queue

What it means

Each queue entry in the channel definition is resolved (possibly via SpEL) and must resolve to a String, a String array/iterable, or an org.springframework.amqp.core.Queue. Any other resolved type makes resolveQueues throw this IllegalArgumentException because the endpoint cannot derive queue names from it.

Source

Thrown at modules/flowable-event-registry-spring/src/main/java/org/flowable/eventregistry/spring/rabbit/RabbitChannelDefinitionProcessor.java:202

        return resultQueues.toArray(new String[0]);
    }

    protected void resolveQueues(Object resolvedValue, List<String> result, RabbitInboundChannelModel channelDefinition) {
        Object resolvedValueToUse = resolvedValue;
        if (resolvedValueToUse instanceof String[]) {
            resolvedValueToUse = Arrays.asList((String[]) resolvedValueToUse);
        }

        if (resolvedValueToUse instanceof String) {
            result.add((String) resolvedValueToUse);
        } else if (resolvedValueToUse instanceof Queue) {
            result.add(((Queue) resolvedValueToUse).getName());
        } else if (resolvedValueToUse instanceof Iterable) {
            for (Object object : (Iterable<?>) resolvedValueToUse) {
                resolveQueues(object, result, channelDefinition);
            }
        } else {
            throw new IllegalArgumentException(
                "Channel definition " + channelDefinition + " cannot resolve " + resolvedValue + " as a String[] or a String or a Queue");
        }
    }

    protected Integer resolvePriority(RabbitInboundChannelModel channelDefinition) {
        String priority = resolve(channelDefinition.getPriority());
        if (StringUtils.hasText(priority)) {
            try {
                return Integer.valueOf(priority);
            } catch (NumberFormatException ex) {
                throw new IllegalArgumentException("Invalid priority value for " +
                    channelDefinition + " (must be an integer)", ex);
            }
        } else {
            return null;
        }
    }

View on GitHub (pinned to d6d39ce1c6)

Solutions

1. Change the expression so it resolves to a queue name String (or list of Strings)
2. If referencing a bean, reference a Queue bean or a String[]/List<String> bean
3. Print/log the resolved value's class to identify the wrong type
4. Fix typos in property keys that cause fallback to unintended values

Example fix

// before
"queues": "${queueProps}"  // resolves to Map<String,String>
// after
"queues": "${queueNames}"  // resolves to List<String> or String[]

Object resolved = resolveExpression(queueExpr);
if (!(resolved instanceof String) && !(resolved instanceof String[]) && !(resolved instanceof Queue) && !(resolved instanceof Iterable)) {
    throw new IllegalArgumentException("Queue expression must resolve to String/String[]/Queue/Iterable, got " + resolved.getClass());
}

boolean isResolvableQueueValue(Object v) {
    return v instanceof String || v instanceof String[] || v instanceof Queue || v instanceof Iterable;
}

try {
    processor.process(definition);
} catch (IllegalArgumentException ex) {
    if (ex.getMessage().contains("cannot resolve")) {
        log.error("Queue expression resolves to unsupported type: {}", ex.getMessage());
    }
    throw ex;
}

When it happens

Trigger: A queue expression resolves to an unsupported type, e.g. a Map, Integer, Boolean, or arbitrary bean, when createRabbitListenerEndpoint processes the queues of an inbound Rabbit channel definition.

Common situations: SpEL pointing at the wrong bean or a Map of queue properties instead of names; placeholder resolving to a Number; typo causing resolution to fall through to an unexpected object; nested list of non-String elements.

Related errors

• The [<attribute>] must resolve to a String. Resolved to [<cl
• Queues in <channelDefinition> must not be null
• Invalid priority value for <channelDefinition> (must be an i
• Could not register rabbit listener endpoint on [<channelDefi
• ackMode in definition [ <channelDefinition> ] must resolve t

AI-assisted analysis of flowable/flowable-engine@d6d39ce1c6 (2026-09-11). Data as JSON: /api/errors/37997a1611d5825f. Report an issue: GitHub.