What is the spring batch way of formatting CSV fields individually?

[Sax388]

Before using Spring Batch I've been using

@Data
public class DataModel{
  @CsvCustomBindByPosition(position = 0, converter = BigDecimalCurrencyConverter.class)
  @CsvBindByName(column = "Revenue (in $)")
  private BigDecimal revenue;
}

with

public static class BigDecimalCurrencyConverter
    extends AbstractBeanField<BigDecimal, BigDecimal> {

  @Override
  protected BigDecimal convert(String value)
      throws CsvDataTypeMismatchException, CsvConstraintViolationException {
    if (value == null || value.isEmpty()) {
      return null;
    }

    var symbols = new DecimalFormatSymbols(Locale.getDefault());
    symbols.setDecimalSeparator(',');

    var decimalFormat = new DecimalFormat("#,##0.00", symbols);
    decimalFormat.setParseBigDecimal(true);

    try {
      return (BigDecimal) decimalFormat.parse(value);
    } catch (ParseException e) {
      throw new RuntimeException(e);
    }
  }

  @Override
  protected String convertToWrite(Object value) {
    if (value == null) {
      return "";
    }

    var number = (BigDecimal) value;

    var symbols = new DecimalFormatSymbols(Locale.getDefault());
    symbols.setDecimalSeparator(',');

    var decimalFormat = new DecimalFormat("#,##0.00", symbols);

    return decimalFormat.format(number);
  }
}

With a little Reflection the fields were (de)serialized accordingly.

Now I'm not sure how exactly to put this code to make the most out of it. I liked having it close to the model. I'm still using

private static <T> String[] getCsvHeaderNames(Class<T> modelClass) {
  return Arrays.stream(modelClass.getDeclaredFields())
      .map(
          field ->
              field.getAnnotation(CsvBindByName.class) != null
                  ? field.getAnnotation(CsvBindByName.class).column()
                  : field.getName())
      .toArray(String[]::new);
}

to get the headers for my FlatFileHeaderCallback.

[fmbenhassine]

The FieldSetMapper is the main extension point for converting a typed fieldset to a domain object. There an are few implementations provided by spring batch, but you might need a custom one if nothing from the provided ones really help.

In your case, you can use a BeanWrapperFieldSetMapper if the target type is a java class or RecordFieldSetMapper for java records. Both provide a configurable conversion service in which you can register custom converter like the one you shared (you just need to adapt it to the expected conversion type).

If you share a GitHub repo or a zip with a minimal code example / input file, I can try to help you implement the mapping logic with spring batch.

[Sax388]

Thanks a million, I was able to use a CustomBeanWrapperFieldExtractor and I'm really happy how it turned out!

  private FlatFileItemWriter<RechnungserstellungRow> createWriter() {
    return new FlatFileItemWriterBuilder<RechnungserstellungRow>()
        .resource(new FileSystemResource(Path.of(outputFile)))
        .name("rechnungserstellungReportFormatFileWriter")
        .headerCallback(new CsvHeaderCallback(csvHeaderNames))
        .delimited()
        .delimiter(";")
        .fieldExtractor(fieldExtractor())
        .shouldDeleteIfEmpty(true)
        .build();
  }

  private CustomBeanWrapperFieldExtractor<RechnungserstellungRow> fieldExtractor() {
    CustomBeanWrapperFieldExtractor<RechnungserstellungRow> fieldExtractor =
        new CustomBeanWrapperFieldExtractor<>();
    fieldExtractor.setNames(csvColumnNames);
    fieldExtractor.afterPropertiesSet();

    fieldExtractor.registerConverter(
        BigDecimal.class, new BigDecimalCurrencyConverter(Locale.GERMAN));

    return fieldExtractor;
  }

And the converter implementation is also nice:

@RequiredArgsConstructor
public class BigDecimalCurrencyConverter implements Converter<BigDecimal, String> {

  private final Locale locale;

  @Override
  public String convert(@NonNull BigDecimal value) {

    var symbols = new DecimalFormatSymbols(locale);
    symbols.setDecimalSeparator(',');

    var decimalFormat = new DecimalFormat("#,##0.00", symbols);
    decimalFormat.setRoundingMode(RoundingMode.HALF_UP);
    decimalFormat.setGroupingUsed(false);
    return decimalFormat.format(value);
  }
}