apache/seatunnel · error · IllegalArgumentException

Cannot convert to BigDecimal:

Error message

Cannot convert to BigDecimal: 

What it means

Iceberg RowConverter throws this when a field value cannot be converted to the target decimal type. It accepts Number (double) and String inputs; anything else reaches the else branch. The class name of the offending value is appended to the message to help identify the source of the bad data.

Source

Thrown at seatunnel-connectors-v2/connector-iceberg/src/main/java/org/apache/seatunnel/connectors/seatunnel/iceberg/data/RowConverter.java:334

                "Cannot convert to double: " + value.getClass().getName());
    }

    protected BigDecimal convertDecimal(Object value, Types.DecimalType type) {
        BigDecimal bigDecimal;
        if (value instanceof BigDecimal) {
            bigDecimal = (BigDecimal) value;
        } else if (value instanceof Number) {
            Number num = (Number) value;
            Double dbl = num.doubleValue();
            if (dbl.equals(Math.floor(dbl))) {
                bigDecimal = BigDecimal.valueOf(num.longValue());
            } else {
                bigDecimal = BigDecimal.valueOf(dbl);
            }
        } else if (value instanceof String) {
            bigDecimal = new BigDecimal((String) value);
        } else {
            throw new IllegalArgumentException(
                    "Cannot convert to BigDecimal: " + value.getClass().getName());
        }
        return bigDecimal.setScale(type.scale(), RoundingMode.HALF_UP);
    }

    protected boolean convertBoolean(Object value) {
        if (value instanceof Boolean) {
            return (boolean) value;
        } else if (value instanceof String) {
            return Boolean.parseBoolean((String) value);
        }
        throw new IllegalArgumentException(
                "Cannot convert to boolean: " + value.getClass().getName());
    }

    protected String convertString(Object value) {
        try {
            if (value instanceof String) {

View on GitHub (pinned to cf67b549a7)

Solutions

1. Inspect the class name in the message and trace which upstream column produced that type.
2. Ensure the SeaTunnel source emits Number or String for decimal fields; configure source type mapping accordingly.
3. Add a transform to cast the column (e.g. CAST to DECIMAL) before the Iceberg sink.
4. If the value is genuinely non-numeric, fix data quality at the source or drop/coerce the field.

Example fix

// before
Object v = rowData.getField(2); // byte[] from upstream
// after
Object v = new String((byte[]) rowData.getField(2)); // or CAST in a transform so converter gets Number/String

if (!(v instanceof Number) && !(v instanceof String)) throw new IllegalArgumentException("decimal column must be Number/String, got " + (v == null ? "null" : v.getClass().getName()));

boolean isDecimalConvertible(Object v) { return v instanceof Number || v instanceof String; }

try { sink.write(row); } catch (IllegalArgumentException e) { if (e.getMessage().startsWith("Cannot convert to BigDecimal")) { log.error("Bad decimal value: {}", e.getMessage()); /* skip or DLQ row */ } else throw e; }

When it happens

Trigger: convertDecimal receives a value that is neither Number nor String while mapping a SeaTunnel row to an Iceberg DECIMAL column, e.g. a Boolean, byte[], or a null-typed boxed object produced upstream.

Common situations: Upstream source emits decimal columns as an unexpected Java type (e.g. CDC deserialization yields byte[] or BigDecimal handled by a different branch); schema mismatch where a string-typed SeaTunnel column maps to a decimal Iceberg column but a nested type slips through.

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

AI-assisted analysis of apache/seatunnel@cf67b549a7 (2026-09-10). Data as JSON: /api/errors/b9afc80ad9156f42. Report an issue: GitHub.