xls (HSSF) Overview

HSSF provides read and write support for the legacy xls (BIFF8) format. Coverage is ~35%.

Status

HSSF has grown beyond the original bootstrap reader/writer. It now supports practical basic workbook operations: common cell types, multiple sheets, basic styles, layout records, representative Apache POI fixture loading, Java POI interop slices, and preservation of non-workbook OLE streams, VBA streams, and unknown BIFF records during light edits.

It is still not a full Apache POI HSSF port. Images, shapes, chart creation, comment editing, filters, pivots, and new BIFF formula token writing are not modeled through public APIs.

Basic Read and Write

using DotnetPoi.HSSF.UserModel;

// Write
using var wb = new HSSFWorkbook();
var sheet = wb.createSheet("Sheet1");
var row = sheet.createRow(0);
row.createCell(0).setCellValue("Hello from HSSF");

using var file = File.Create("output.xls");
wb.write(file);

// Read
using var stream = File.OpenRead("input.xls");
using var wb2 = new HSSFWorkbook(stream);
var value = wb2.getSheetAt(0).getRow(0).getCell(0).getStringCellValue();

When to Use HSSF

• You need to read or update existing xls files without style changes
• You have a legacy workflow that requires xls output
• You are migrating from xls to xlsx and need a transitional solution
• You need to extract values from old xls files for indexing or migration
• You need light edits while preserving unmodeled OLE/BIFF content as much as possible

When to Use XSSF Instead

• All new development should use XSSF (xlsx)
• xlsx is more capable, more widely supported, and has higher coverage
• Excel can open xlsx files from Excel 2007 onwards
• LibreOffice/OpenOffice handles xlsx as well as xls

Supported Today

• String, numeric, boolean, blank, and error cells
• Multiple sheets, sparse rows/cells, and high column indexes
• Basic font and cell style round-trips: font name/size/bold/italic/color, data formats, alignment, wrap, borders, fills
• Column width, row height, hidden rows/columns, merged regions, freeze panes
• Reading formula text and cached formula values from existing files
• Representative Apache POI .xls fixture loading
• Java POI interop fixtures for basic, styles, layout, unicode, and comprehensive workbooks
• Preservation of non-Workbook OLE streams, macro/VBA streams, directory metadata, and unknown BIFF records

Limitations

• No formula evaluation
• No new BIFF formula token writing
• No image or drawing usermodel
• No chart creation/editing
• No comment or hyperlink editing API
• No data validation
• No auto filter
• No pivot tables
• No rich text

HSSF is maintained for compatibility but is not a priority for new development.