apache/seatunnel · error · IllegalArgumentException

Cannot convert to binary:

Error message

Cannot convert to binary: 

What it means

Iceberg RowConverter throws this when a binary column value is not String (Base64), byte[], or ByteBuffer. convertBase64Binary supports exactly those three representations; anything else is rejected with the class name in the message.

Source

Thrown at seatunnel-connectors-v2/connector-iceberg/src/main/java/org/apache/seatunnel/connectors/seatunnel/iceberg/data/RowConverter.java:383

    protected UUID convertUUID(Object value) {
        if (value instanceof String) {
            return UUID.fromString((String) value);
        } else if (value instanceof UUID) {
            return (UUID) value;
        }
        throw new IllegalArgumentException("Cannot convert to UUID: " + value.getClass().getName());
    }

    protected ByteBuffer convertBase64Binary(Object value) {
        if (value instanceof String) {
            return ByteBuffer.wrap(Base64.getDecoder().decode((String) value));
        } else if (value instanceof byte[]) {
            return ByteBuffer.wrap((byte[]) value);
        } else if (value instanceof ByteBuffer) {
            return (ByteBuffer) value;
        }
        throw new IllegalArgumentException(
                "Cannot convert to binary: " + value.getClass().getName());
    }

    protected LocalDate convertDateValue(Object value) {
        if (value instanceof Number) {
            int days = ((Number) value).intValue();
            return DateTimeUtil.dateFromDays(days);
        } else if (value instanceof String) {
            return LocalDate.parse((String) value);
        } else if (value instanceof LocalDate) {
            return (LocalDate) value;
        } else if (value instanceof Date) {
            int days = (int) (((Date) value).getTime() / 1000 / 60 / 60 / 24);
            return DateTimeUtil.dateFromDays(days);
        }
        throw new RuntimeException("Cannot convert date: " + value);
    }

View on GitHub (pinned to cf67b549a7)

Solutions

1. Ensure the source emits byte[] or Base64-encoded String for binary fields.
2. Add a transform to encode the value as Base64 string before the sink.
3. Verify SeaTunnel schema maps the column to BytesType, not another type.

Example fix

// before
writer.write(idx, someCustomBlobObject);
// after
writer.write(idx, Base64.getEncoder().encodeToString(blobBytes)); // String accepted

if (!(v instanceof String) && !(v instanceof byte[]) && !(v instanceof ByteBuffer)) throw new IllegalArgumentException("binary column must be String/byte[]/ByteBuffer, got " + (v == null ? "null" : v.getClass().getName()));

boolean isBinaryConvertible(Object v) { return v instanceof String || v instanceof byte[] || v instanceof ByteBuffer; }

try { sink.write(row); } catch (IllegalArgumentException e) { if (e.getMessage().startsWith("Cannot convert to binary")) { /* encode to Base64 or DLQ */ } else throw e; }

When it happens

Trigger: convertBase64Binary receives e.g. an Integer, BigDecimal, or arbitrary object while converting a field to an Iceberg BINARY column.

Common situations: Binary data serialized as JSON arrays/ints by a non-conforming source; nested structures mistakenly mapped to BINARY; file sources emitting image bytes wrapped in custom types.

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

• Cannot convert to BigDecimal:
• Cannot convert to boolean:
• Cannot convert to UUID:
• Cannot convert date:
• Cannot convert time:

AI-assisted analysis of apache/seatunnel@cf67b549a7 (2026-09-10). Data as JSON: /api/errors/2eb7b291c8637ef1. Report an issue: GitHub.