DotnetPoi.Core 0.5.0

DotnetPoi.Core

Faithful .NET port of Apache POI — read/write xlsx, docx, pptx, xls, doc, ppt with zero dependencies.

⚠️ This is an unofficial port and is not affiliated with the Apache Software Foundation. Apache POI is a registered trademark of the Apache Software Foundation.

Install

dotnet add package DotnetPoi.Core

<PackageReference Include="DotnetPoi.Core" Version="0.5.0" />

Compatible with .NET 5+, .NET Core 3.1+, .NET Framework 4.7.2+, Mono 5.4+, Unity 2018.1+.

Documentation

Full documentation is available at the dotnet-poi documentation site

Package architecture

DotnetPoi.Core contains everything except formula evaluation. Formulas are preserved as text and cached values are read/written, but the evaluator engine lives in the separate DotnetPoi.Formula package. When DotnetPoi.Formula is referenced, createFormulaEvaluator() is automatically enabled via lazy assembly discovery at runtime.

Quick start

xlsx — write

using DotnetPoi.XSSF.UserModel;

using var wb = new XSSFWorkbook();
var sheet = wb.createSheet("Sheet1");
var row = sheet.createRow(0);
row.createCell(0).setCellValue("Hello");
row.createCell(1).setCellValue(42);

using var fs = new FileStream("output.xlsx", FileMode.Create);
wb.write(fs);

xlsx — read

using var fs = new FileStream("input.xlsx", FileMode.Open);
using var wb = new XSSFWorkbook(fs);

var cell = wb.getSheetAt(0).getRow(0).getCell(0);
Console.WriteLine(cell.getStringCellValue());

xlsx — styling

using DotnetPoi.SS.UserModel;

var style = wb.createCellStyle();
style.setFillForegroundColor(IndexedColors.Green.getIndex());
style.setFillPattern(FillPatternType.SolidForeground);
style.setBorderTop(BorderStyle.Thin);
var cell = sheet.createRow(0).createCell(0);
cell.setCellValue("Styled");
cell.setCellStyle(style);

docx — write

using DotnetPoi.XWPF.UserModel;

using var doc = new XWPFDocument();
var run = doc.createParagraph().createRun();
run.setText("Hello from dotnet-poi");
run.setBold(true);

using var fs = new FileStream("output.docx", FileMode.Create);
doc.write(fs);

pptx — write

using DotnetPoi.XSLF.UserModel;

using var prs = new XMLSlideShow();
var slide = prs.createSlide();
var picIdx = prs.addPicture(File.ReadAllBytes("photo.jpeg"), XSLFPictureData.PICTURE_TYPE_JPEG);
var shape = prs.createPicture(slide, picIdx);
shape.setAnchor(0, 0, XMLSlideShow.DefaultSlideCx, XMLSlideShow.DefaultSlideCy);
shape.setRotation(45.0);

using var fs = new FileStream("output.pptx", FileMode.Create);
prs.write(fs);

Encrypted xlsx

using var wb = new XSSFWorkbook();
wb.createSheet("Sheet1").createRow(0).createCell(0).setCellValue("Secret");
using var fs = new FileStream("secret.xlsx", FileMode.Create);
wb.writeEncrypted(fs, "password123");

Format coverage

Legend: ✅ complete / ⚠️ partial / 🔵 preserved as unknown parts, not editable / ❌ not implemented.

xlsx / XSSF (~78%)

docx / XWPF (~65%)

pptx / XSLF (~40%)

xls / HSSF (~10%)

Legacy binary

Practical gaps (priority order)

Test coverage

Testing strategy

Quality and fidelity to Apache POI are ensured through a multi-layered testing strategy:

• Unit tests (xUnit): Ported alongside each class from the original Apache POI test suite. Ensures internal logic and edge-case handling are consistent with Java.
• XML Parity tests: Captures raw XML output from Apache POI (via XMLBeans) and verifies that PoiXmlWriter produces byte-equivalent output in C#. This prevents interoperability issues caused by subtle XML formatting differences.
• Bidirectional Interop tests:
  • Direction A: Java POI writes a file → DotnetPoi.Core reads it.
  • Direction B: DotnetPoi.Core writes a file → Java POI reads it.
• Preservation tests: Verifies that unmodeled features (macros, charts, comments, pivot tables) survive a read-modify-write cycle (round-trip) without data loss.
• Manual Verification: Periodic verification using real Office applications (Excel, Word, PowerPoint) and LibreOffice on macOS, Windows, and Linux to ensure no "repair" dialogs or visual regressions.

Philosophy

• 🔱 Maximum fidelity to upstream Apache POI — we follow, not reinvent
• 🤖 Ported class-by-class with LLM assistance
• 💸 Free forever. No EULA. No maintenance fee. No exceptions.
• 📖 Apache POI is the source of truth — included as a git submodule

License

Apache License 2.0 — same as upstream Apache POI.

Disclaimer

This project is not affiliated with the Apache Software Foundation or the Apache POI project. Apache POI is a registered trademark of the Apache Software Foundation.