apache/beam · error · IllegalArgumentException

Unsupported field type: {type}

Error message

Unsupported field type: {type}

What it means

RowJson's serializer (RowJsonCreator's generator) writes Row fields by schema type and handles only a fixed set of types in its switch. Encountering an unsupported Schema.Type in writeValue throws IllegalArgumentException 'Unsupported field type'.

Source

Thrown at sdks/java/core/src/main/java/org/apache/beam/sdk/util/RowJson.java:617

            gen.writeFieldName(entry.getKey().toString());
            writeValue(gen, type.getMapValueType(), entry.getValue());
          }
          gen.writeEndObject();
          break;
        case LOGICAL_TYPE:
          String identifier = type.getLogicalType().getIdentifier();
          if (SqlTypes.DATE.getIdentifier().equals(identifier)) {
            gen.writeString(((LocalDate) value).toString()); // ISO 8601 format
          } else if (SqlTypes.TIME.getIdentifier().equals(identifier)) {
            gen.writeString(((LocalTime) value).toString()); // ISO 8601 format
          } else if (SqlTypes.DATETIME.getIdentifier().equals(identifier)) {
            gen.writeString(((LocalDateTime) value).toString()); // ISO 8601 format
          } else {
            writeValue(gen, type.getLogicalType().getBaseType(), value);
          }
          break;
        default:
          throw new IllegalArgumentException("Unsupported field type: " + type);
      }
    }
  }

  /** Gets thrown when Row parsing or serialization fails for any reason. */
  public static class UnsupportedRowJsonException extends RuntimeException {

    UnsupportedRowJsonException(String message, Throwable reason) {
      super(message, reason);
    }

    UnsupportedRowJsonException(String message) {
      super(message);
    }
  }
}

View on GitHub (pinned to 12126d8942)

Solutions

1. Check the switch in RowJson.RowWriter.writeValue and only serialize supported types
2. Convert unsupported fields to supported types (e.g. logical type to its base type or String) before serialization
3. Register/handle the logical type explicitly, or flatten the schema
4. Catch IllegalArgumentException around rowToJson to handle offending rows

Example fix

// before: field of unsupported logical type serialized directly
rowToJson(mapper, rowWithCustomLogicalType);
// after: convert to base type/string first
Row fixed = rowFrom(ROW_SCHEMA).withFieldValue("ts", ts.toString()).build();
rowToJson(mapper, fixed);

boolean allSupported = row.getSchema().getFields().stream()
    .allMatch(f -> SUPPORTED_WRITER_TYPES.contains(f.getType().getTypeName()));
if (!allSupported) { /* convert or skip row */ }

try { String s = RowJsonUtils.rowToJson(mapper, row); } catch (IllegalArgumentException e) { /* row contains unsupported field type */ }

When it happens

Trigger: Serializing a Row (RowJsonUtils.rowToJson or objectMapper.writeValueAsString on a Row) whose schema contains a field type not covered by the writer's switch (e.g. certain logical or nested types it does not handle directly).

Common situations: Rows built with logical types or newer Beam types not yet supported by the JSON writer; schema evolution introduced an exotic type; custom logical types.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• Unable to serialize row: {row}
• Cannot provide SerializableCoder because {} does not impleme
• Java Serialization may be non-deterministic.
• cannot encode a null String
• cannot encode a null Integer

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/ca15c37b30275485. Report an issue: GitHub.