apache/iceberg · error · IllegalArgumentException

Cannot convert to boolean

Error message

Cannot convert to boolean: ${value.getClass().getName()}

What it means

convertBoolean converts values to Iceberg BooleanType fields: it accepts Boolean directly and String via Boolean.parseBoolean. Note parseBoolean treats any non-"true" string as false, so only non-String/non-Boolean classes (Number, byte[], Map, List) throw IllegalArgumentException.

Solutions

1. Send actual Boolean values (or "true"/"false" strings) for boolean fields.
2. If the producer emits 0/1, add an SMT to convert ints to booleans, or change the column to IntegerType.
3. Change the Iceberg column type to match the actual data type.
4. Catch IllegalArgumentException to divert records to a DLQ.

Example fix

// before
record.set("active", 1); // int into BooleanType
// after
record.set("active", true); // or SMT: ReplaceField with cast, or column INTEGER

Object v = record.get("active");
if (!(v instanceof Boolean) && !(v instanceof String)) {
  throw new IllegalArgumentException("active must be boolean, got " + v.getClass().getSimpleName());
}

boolean isBooleanConvertible(Object v) {
  return v instanceof Boolean || v instanceof String;
}

try {
  sink.write(record);
} catch (IllegalArgumentException e) {
  if (e.getMessage() != null && e.getMessage().contains("Cannot convert to boolean")) {
    sendToDlq(record, e);
  } else throw e;
}

When it happens

Trigger: A field mapped to an Iceberg BooleanType column holding a Number, byte[], collection, or other value that is neither Boolean nor String.

Common situations: Boolean columns fed 0/1 integer values from producers (a common mismatch — numbers are NOT accepted here); schemaless JSON with mixed types; legacy producers using int flags.

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 double
• Cannot convert to float
• Cannot convert to int
• Cannot convert to long

AI-assisted analysis of apache/iceberg@86d9c8fc54 (2026-09-12). Data as JSON: /api/errors/96fdc02f97b71f91. Report an issue: GitHub.

Appendix: source

Thrown at kafka-connect/kafka-connect/src/main/java/org/apache/iceberg/connect/data/RecordConverter.java:486

      } 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) {
        return (String) value;
      } else if (value instanceof Number || value instanceof Boolean) {
        return value.toString();
      } else if (value instanceof Map || value instanceof List) {
        return MAPPER.writeValueAsString(value);
      } else if (value instanceof Struct) {
        Struct struct = (Struct) value;
        byte[] data = config.jsonConverter().fromConnectData(null, struct.schema(), struct);
        return new String(data, StandardCharsets.UTF_8);
      }
    } catch (IOException e) {
      throw new UncheckedIOException(e);
    }

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