apache/beam · error · UnsupportedRowJsonException

Expected JSON object for field '{name}'. Instead got {jsonNo

Error message

Expected JSON object for field '{name}'. Instead got {jsonNodeType}

What it means

For MAP-typed schema fields, jsonObjectToMap requires the JSON value to be an object whose keys become map keys. A different JSON node type causes UnsupportedRowJsonException that names the encountered Jackson node type.

Source

Thrown at sdks/java/core/src/main/java/org/apache/beam/sdk/util/RowJson.java:387

                + "'. Instead got "
                + arrayFieldValue.jsonNodeType().name());
      }

      return arrayFieldValue
          .jsonArrayElements()
          .map(
              jsonArrayElement ->
                  extractJsonNodeValue(
                      FieldValue.of(
                          arrayFieldValue.name() + "[]",
                          arrayFieldValue.arrayElementType(),
                          jsonArrayElement)))
          .collect(toImmutableList());
    }

    private Map<String, Object> jsonObjectToMap(FieldValue mapFieldValue) {
      if (!mapFieldValue.isJsonObject()) {
        throw new UnsupportedRowJsonException(
            "Expected JSON object for field '"
                + mapFieldValue.name()
                + "'. Instead got "
                + mapFieldValue.jsonNodeType().name());
      }

      Map<String, Object> result = new HashMap<>();
      Iterator<Map.Entry<String, JsonNode>> fields = mapFieldValue.jsonValue().fields();
      while (fields.hasNext()) {
        Map.Entry<String, JsonNode> field = fields.next();
        String key = field.getKey();
        JsonNode value = field.getValue();

        Object extractedValue =
            extractJsonNodeValue(
                FieldValue.of(
                    mapFieldValue.name() + "['" + key + "']", mapFieldValue.mapValueType(), value));

View on GitHub (pinned to 12126d8942)

Solutions

Emit the map field as a JSON object, e.g. "props": {"k": "v"}
Change the schema field type (e.g. to ARRAY<ROW<k,v>>) to match the payload
Convert list-of-pairs JSON to an object before parsing
Catch UnsupportedRowJsonException and route bad records to error handling

Example fix

// before
{"props": [{"k":"a","v":1}]}
// after
{"props": {"a": 1}}

Defensive patterns

Strategy: validation

Validate before calling

JsonNode n = json.get("mapField");
if (n != null && !n.isObject()) throw new IllegalArgumentException("Map field must be a JSON object, got " + n.getNodeType());

Try / catch

try { Row r = RowJsonUtils.jsonToRow(mapper, json); } catch (RowJson.UnsupportedRowJsonException e) { /* handle */ }

Prevention

Serialize maps as JSON objects, not arrays of pairs
Document map encoding for producers
Validate payloads against MAP-typed fields

When it happens

Trigger: jsonToRow where a MAP<...> schema field receives a non-object JSON value, e.g. "props": "k=v" or an array instead of an object.

Common situations: Producers serializing maps as lists of key/value pairs; schema changed from array to map; generic JSON ingestion with mismatched reader schema.

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 apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/41eb2087226139d8. Report an issue: GitHub.