I am generating an .xlsx file using Apache POI 5.2.5, sending the byte array to the client side and downloading the file locally on the client’s machine.

When trying to open the file, I’m getting “We found a problem with some content in *.xlsx. Do you want us to try to recover it as much as we can” error. Clicking yes the file opens both on Windows and on Mac and all the data is present, but not as a table object. Trying to open the file using google sheets works without issues and the table object has a border.

The issue persisted also when I tried to save it directly on the server’s machine, so I don’t think the problem is on the client side.

The code generating the byte array:

private byte[] generateExcelBytes(List<DATA_OBJECT> data) {
    try (XSSFWorkbook workbook = new XSSFWorkbook()) {
        XSSFSheet sheet = workbook.createSheet("Data");

        CellStyle headerStyle = workbook.createCellStyle();
        Font headerFont = workbook.createFont();
        headerFont.setBold(true);
        headerFont.setFontHeightInPoints((short) 14);
        headerStyle.setFont(headerFont);

        CellStyle dataStyle = workbook.createCellStyle();
        Font dataFont = workbook.createFont();
        dataFont.setFontHeightInPoints((short) 12);
        dataStyle.setFont(dataFont);

        createTable(sheet, 0, 0, headerStyle, dataStyle, data);

        // Write the workbook content to a ByteArrayOutputStream
        ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
        workbook.write(outputStream);
        return outputStream.toByteArray();
    } catch (IOException e) {
        logger.error("Exception when creating xlsx file for account {} CDI status tables", account.getId(), e);
    }
    return null;
}

private void createTable(XSSFSheet sheet, int startRow, int startCol, CellStyle headerStyle, CellStyle dataStyle, List<DATA_OBJECT> data) {
    // Create sample data (replace with your actual data generation logic)
    Row headerRow = sheet.createRow(startRow);

    // for each header
    createCell(headerRow, startCol + X, HEADER_NAME, headerStyle);

    // Create data rows
    for (int i = 0; i < data.size(); i++) {
        DATA_OBJECT data_object = data.get(i);
        Row dataRow = sheet.createRow(startRow + i + 1);
        // for each data object
        createCell(dataRow, startCol, data_object.get_relevant_value, dataStyle);
    }

    int endRow = startRow + baseHoldings.size();
    int endCol = startCol + NUM_OF_COLUMNS;

    XSSFAutoFilter autoFilter = sheet.setAutoFilter(new CellRangeAddress(startRow, endRow, startCol, endCol));
    for (int i = startCol; i <= startCol + NUM_OF_COLUMNS; i++) {
        sheet.autoSizeColumn(i);
        sheet.setColumnWidth(i, sheet.getColumnWidth(i) + 1000);
    }

    // Create Excel table
    XSSFTable table = sheet.createTable(null);

    CTTable cttable = table.getCTTable();
    cttable.setDisplayName("Data Table");
    cttable.setId(1);
    cttable.setName("Data_Table");
    cttable.setRef(new CellRangeAddress(startRow, endRow, startCol, endCol).formatAsString());
}

private void createCell(Row row, int columnIndex, String value, CellStyle style) {
    Cell cell = row.createCell(columnIndex);
    cell.setCellValue(value);
    cell.setCellStyle(style);
}

Opening the file on Mac, I managed to see an actual error:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<recoveryLog xmlns="http://schemas.openxmlformats.org/spreadsheetml/2006/main">
    <logFileName>Repair Result to <FILE_NAME>0.xml</logFileName>
    <summary>Errors were detected in file '<FILE_PATH>.xlsx'</summary>
    <removedParts summary="Following is a list of removed parts:">
        <removedPart>Removed Part: /xl/tables/table1.xml part with XML error.  (Table) Xml parsing error Line 2, column 70.</removedPart>
    </removedParts>
</recoveryLog>

/xl/tables/table1.xml file contents:

<?xml version="1.0" encoding="UTF-8"?>
<table id="1" displayName="Data Table" name="Data_Table" ref="A1:H3" xmlns="http://schemas.openxmlformats.org/spreadsheetml/2006/main"/>

I don’t know what causes the XML parsing error, or how to avoid it when generating the file on the server side.
Any help will be appreciated.