Exporting Multiple Header Rows

[brunoagretti]

Describe the bug

When exporting a grid that contains multiple header rows, the exporter only takes the last header row into account and omits the previous ones. This affects the correct representation of headers in the exported file.

Grid with multiple header rows:

Exported .xlsx file:

Expected behavior

The exporter should be able to handle multiple header rows, exporting all of them instead of just the last one. I assume the same issue might occur with footer rows.

Minimal reproducible example

public class GridExporterMultipleHeaderRowsDemo extends Div {

  public GridExporterMultipleHeaderRowsDemo() throws EncryptedDocumentException, IOException {
    Grid<Person> grid = new Grid<>(Person.class);
    DecimalFormat decimalFormat = new DecimalFormat("$#,###.##");
    grid.removeAllColumns();
    grid.addColumn(
            LitRenderer.<Person>of("<b>${item.name}</b>").withProperty("name", Person::getName))
        .setHeader("Name");
    grid.addColumn("lastName").setHeader("Last Name");
    grid.addColumn(item -> Faker.instance().lorem().characters(30, 50)).setHeader("Big column");
    Column<Person> budgetColumn =
        grid.addColumn(item -> decimalFormat.format(item.getBudget()))
            .setHeader("Budget")
            .setTextAlign(ColumnTextAlign.END);
    BigDecimal[] total = new BigDecimal[1];
    total[0] = BigDecimal.ZERO;
    Stream<Person> stream =
        IntStream.range(0, 100)
            .asLongStream()
            .mapToObj(
                number -> {
                  Faker faker = new Faker();
                  Double budget = faker.number().randomDouble(2, 10000, 100000);
                  total[0] = total[0].add(BigDecimal.valueOf(budget));
                  budgetColumn.setFooter(new DecimalFormat("$#,###.##").format(total[0]));
                  return new Person(
                      faker.name().firstName(),
                      (Math.random() > 0.3 ? faker.name().lastName() : null),
                      faker.number().numberBetween(15, 50),
                      budget);
                });
    
    grid.setItems(DataProvider.fromStream(stream));
    grid.setWidthFull();
    this.setSizeFull();
    
	HeaderRow firstExtraHeaderRow = grid.appendHeaderRow();
	HeaderRow secondExtraHeaderRow = grid.appendHeaderRow();
	for (Column<Person> column : grid.getColumns()) {
		String columnHeader = grid.getHeaderRows().get(0).getCell(column).getText();
		
		HeaderCell firstHeaderCell = firstExtraHeaderRow.getCell(column);
		firstHeaderCell.setComponent(new Span(columnHeader + " 1"));
		HeaderCell secondHeaderCell = secondExtraHeaderRow.getCell(column);
		secondHeaderCell.setComponent(new Span(columnHeader + " 2"));
	}

    GridExporter<Person> exporter =
        GridExporter.createFor(grid, "/custom-template.xlsx", "/custom-template.docx");
    HashMap<String, String> placeholders = new HashMap<>();
    placeholders.put("${date}", new SimpleDateFormat().format(Calendar.getInstance().getTime()));
    exporter.setAdditionalPlaceHolders(placeholders);
    exporter.setSheetNumber(1);
    exporter.setCsvExportEnabled(false);
    exporter.setNumberColumnFormat(budgetColumn, decimalFormat, "$#,###.##");
    exporter.setTitle("People information");
    exporter.setNullValueHandler(() -> "(No lastname)");
    exporter.setFileName(
        "GridExport" + new SimpleDateFormat("yyyyddMM").format(Calendar.getInstance().getTime()));
    add(grid);
  }
}

Add-on Version

1.9.2-SNAPSHOT

Vaadin Version

23.3.15

Additional information

No response