What causes " : couldn't convert Long to String " in pentaho/pentaho-kettle?

Verify the conversion mask is a valid DecimalFormat pattern for integers (e.g. '#,##0')

pentaho/pentaho-kettle · error · KettleValueException

<toString()> : couldn't convert Long to String

Error message

<toString()> : couldn't convert Long to String

What it means

Thrown by ValueMetaBase's Long/Integer-to-String conversion when getDecimalFormat(false).format(integer) throws. It wraps the cause and names the value meta, meaning the integer could not be formatted to a string under the current format mask and locale.

Solutions

Verify the conversion mask is a valid DecimalFormat pattern for integers (e.g. '#,##0')
Clear the mask to use the default formatting if none is required
Align setConversionLocale with the mask's separators
Catch KettleValueException and fall back to String.valueOf(long)

Example fix

// before
valueMeta.setConversionMask("#,##0.00E0;;"); // invalid for Integer
// after
valueMeta.setConversionMask("#,##0");

Defensive patterns

Strategy: try-catch

Validate before calling

static boolean isValidIntegerMask(String mask) {
  try { new java.text.DecimalFormat(mask); return true; }
  catch (IllegalArgumentException e) { return false; }
}

Try / catch

try {
  String s = valueMeta.getString(longObject);
} catch (KettleValueException e) {
  log.error("Long->String format failed: " + e.getMessage(), e);
  return String.valueOf(longObject);
}

Prevention

Use integer-appropriate masks like '#,##0' (no decimal sections)
Clear the conversion mask when default formatting is acceptable
Keep mask and ConversionLocale consistent
Test formatting after loading metadata from older files

When it happens

Trigger: Calling getString() on a TYPE_INTEGER value when DecimalFormat.format(Long) fails — invalid conversion mask pattern, incompatible mask/locale combination, or an exception raised inside the DecimalFormat.

Common situations: Masks containing invalid pattern characters copied from a Number field; locale changed after masks were defined; corrupted value meta metadata loaded from an old file.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

Related errors

AI-assisted analysis of pentaho/pentaho-kettle@f3058517a1 (2026-09-13). Data as JSON: /api/errors/c36e281c0b989871. Report an issue: GitHub.

Appendix: source

Thrown at core/src/main/java/org/pentaho/di/core/row/value/ValueMetaBase.java:1312

        return null;
      } else {
        // Return strings padded to the specified length...
        // This is done for backward compatibility with 2.5.x
        // We just optimized this a bit...
        //
        String[] emptyPaddedStrings = Const.getEmptyPaddedStrings();
        if ( length < emptyPaddedStrings.length ) {
          return emptyPaddedStrings[length];
        } else {
          return Const.rightPad( "", length );
        }
      }
    }

    try {
      return getDecimalFormat( false ).format( integer );
    } catch ( Exception e ) {
      throw new KettleValueException( toString() + " : couldn't convert Long to String ", e );
    }
  }

  protected synchronized String convertIntegerToCompatibleString( Long integer ) throws KettleValueException {
    if ( integer == null ) {
      return null;
    }
    return Long.toString( integer );
  }

  protected synchronized Long convertStringToInteger( String string ) throws KettleValueException {
    string = Const.trimToType( string, getTrimType() ); // see if trimming needs
    // to be performed before
    // conversion

    if ( Utils.isEmpty( string ) ) {
      return null;
    }

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