What causes "input is not Array" in alibaba/spring-ai-alibaba?

Use Mode.LIST instead — Jackson and most nodes produce Lists, not arrays.

alibaba/spring-ai-alibaba · error · RuntimeException

input is not Array

Error message

input is not Array

What it means

In ARRAY mode, ListOperatorNode.apply requires the state value at inputKey to be a non-null Java array (inputObject.getClass().isArray()). If the value is null or not an array (List, String, etc.) this RuntimeException is thrown before the Arrays.asList cast.

Solutions

Use Mode.LIST instead — Jackson and most nodes produce Lists, not arrays.
Ensure the upstream node genuinely writes a primitive/object array under inputKey.
Add a null/type check on t.value(inputKey) in an upstream validation step.
Wrap in try-catch mapping this error to a workflow-level failure message.

Example fix

// before
ListOperatorNode.<Item>start().mode(Mode.ARRAY).inputKey("items")... // items is a List
// after
ListOperatorNode.<Item>start().mode(Mode.LIST).inputKey("items")...

Defensive patterns

Strategy: type-guard

Validate before calling

Object v = state.value("items").orElse(null);
if (v == null || !v.getClass().isArray()) throw new IllegalStateException("'items' must be an array, got " + (v == null ? "null" : v.getClass()));

Type guard

boolean isArrayInput(OverAllState state, String key) {
    return state.value(key).map(v -> v != null && v.getClass().isArray()).orElse(false);
}

Try / catch

try {
    out = listOperator.apply(state);
} catch (RuntimeException e) {
    if ("input is not Array".equals(e.getMessage())) {
        throw new IllegalStateException("State holds no array; prefer Mode.LIST for JSON-sourced data", e);
    }
    throw e;
}

Prevention

Avoid Mode.ARRAY unless a node explicitly emits Java arrays.
JSON arrays deserialize to Lists, not arrays — use LIST.
Check for null state values before graph execution.
Prefer LIST mode as the default and document exceptions.

When it happens

Trigger: Mode ARRAY configured while the state value under inputKey is null, a List, or a String; upstream node never ran or wrote a different structure.

Common situations: Assuming JSON arrays in state become Java arrays (they become Lists via Jackson); passing optional state values that may be absent.

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

AI-assisted analysis of alibaba/spring-ai-alibaba@f82da0b50f (2026-09-09). Data as JSON: /api/errors/42cd7af5e7e95456. Report an issue: GitHub.

Appendix: source

Thrown at spring-boot-starters/spring-ai-alibaba-starter-builtin-nodes/src/main/java/com/alibaba/cloud/ai/graph/node/ListOperatorNode.java:104

			Object inputObject = t.value(inputKey).orElse(null);
			List<T> inputList = switch (mode) {
				case JSON_STR -> {
					if (!(inputObject instanceof String)) {
						throw new RuntimeException("input is not String");
					}
					String inputJsonString = inputObject.toString();
					JavaType javaType = objectMapper.getTypeFactory().constructParametricType(List.class, type);
					yield objectMapper.readValue(inputJsonString, javaType);
				}
				case LIST -> {
					if (!(inputObject instanceof List)) {
						throw new RuntimeException("input is not List");
					}
					yield (List<T>) inputObject;
				}
				case ARRAY -> {
					if (inputObject == null || !inputObject.getClass().isArray()) {
						throw new RuntimeException("input is not Array");
					}
					yield Arrays.asList((T[]) inputObject);
				}
			};
			List<T> listElements = inputList.stream()
				.filter(filterChain)
				.sorted(comparatorChain)
				.limit(limitNumber != null && limitNumber > 0 ? limitNumber : Long.MAX_VALUE)
				.toList();

			Object output = switch (mode) {
				case JSON_STR -> objectMapper.writeValueAsString(listElements);
				case LIST -> listElements;
				case ARRAY -> listElements.toArray();
			};

			return Map.of(outputKey, output);
		}

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