apache/beam · error · UnsupportedRowJsonException

Field type%s %s not supported when converting between JSON a

Error message

Field type%s %s not supported when converting between JSON and Rows. Supported types are: %s

What it means

RowJson.verifySchemaSupported scans a Schema and throws UnsupportedRowJsonException if any field has a type not supported by Beam's Row-to-JSON conversion. The message lists the unsupported fields and the set of supported types. This is a pre-flight validation for JSON serialization of Rows.

Source

Thrown at sdks/java/core/src/main/java/org/apache/beam/sdk/util/RowJson.java:117

})
public class RowJson {
  private static final ImmutableSet<TypeName> SUPPORTED_TYPES =
      ImmutableSet.of(
          BYTE, INT16, INT32, INT64, FLOAT, DOUBLE, BOOLEAN, STRING, DECIMAL, DATETIME, MAP);
  private static final ImmutableSet<String> KNOWN_LOGICAL_TYPE_IDENTIFIERS =
      ImmutableSet.of(
          SqlTypes.DATE.getIdentifier(),
          SqlTypes.TIME.getIdentifier(),
          SqlTypes.DATETIME.getIdentifier());

  /**
   * Throws {@link UnsupportedRowJsonException} if {@code schema} contains an unsupported field
   * type.
   */
  public static void verifySchemaSupported(Schema schema) {
    ImmutableList<UnsupportedField> unsupportedFields = findUnsupportedFields(schema);
    if (!unsupportedFields.isEmpty()) {
      throw new UnsupportedRowJsonException(
          String.format(
              "Field type%s %s not supported when converting between JSON and Rows. Supported types are: %s",
              unsupportedFields.size() > 1 ? "s" : "",
              unsupportedFields.toString(),
              SUPPORTED_TYPES.toString()));
    }
  }

  private static class UnsupportedField {
    final String descriptor;
    final TypeName typeName;

    UnsupportedField(String descriptor, TypeName typeName) {
      this.descriptor = descriptor;
      this.typeName = typeName;
    }

    @Override

View on GitHub (pinned to 12126d8942)

Solutions

Remove or transform unsupported fields (map them to supported types) before JSON conversion.
Check SUPPORTED_TYPES in RowJson to confirm which field types are allowed.
Use a logical type with a supported base type or convert to STRING manually.
Flatten or drop nested unsupported structures before serialization.

Example fix

// before
RowJson.RowToJsonConverter converter = RowJson.RowToJsonConverter.forSchema(schema); // throws
// after
Schema trimmed = schema;
for (UnsupportedField f : RowJson.findUnsupportedFields(schema)) {
  trimmed = Schema.builder().addFields(.../* exclude or remap f */...).build();
}

Defensive patterns

Strategy: validation

Validate before calling

try {
  RowJson.verifySchemaSupported(schema);
} catch (UnsupportedRowJsonException e) {
  // remap/drop unsupported fields before building the converter
}

Try / catch

try {
  converter = RowJson.RowToJsonConverter.forSchema(schema);
} catch (UnsupportedRowJsonException e) {
  schema = sanitizeSchema(schema); // remove/remap unsupported field types
  converter = RowJson.RowToJsonConverter.forSchema(schema);
}

Prevention

Run verifySchemaSupported as a startup check for any Row<->JSON path.
Keep schemas limited to types in RowJson.SUPPORTED_TYPES.
Convert logical/custom types to supported base types (e.g. STRING) at ingest.
Add a test asserting schema-to-JSON compatibility on schema changes.

When it happens

Trigger: Calling RowJson.toJson / creating a RowJson converter for a schema containing an unsupported field type (per SUPPORTED_TYPES), verified via verifySchemaSupported(schema).

Common situations: Schemas containing logical types, MAP/ARRAY of unsupported element types, or custom types that have no JSON mapping; schema evolved to add such a field after JSON export was built.

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

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/0cf84e9ec91372be. Report an issue: GitHub.