Apache POI Tutorial

What is Apache POI? Apache POI is the open source Java library for Microsoft Office formats. The components you will use most are HSSF/XSSF (Excel .xls / .xlsx ), HWPF/XWPF (Word ...

Maven Dependency Gradle Dependency Without a Build Tool (Eclipse) Download the POI binary distribution, unzip it, then Project → Properties → Java Build Path → Libraries → Add ...

XSSFWorkbook in 10 Lines Key Points Always use try-with-resources : both Workbook and the output stream must be closed. Rows and cells are 0-indexed . setCellValue is overloaded ...

Iterate Rows and Cells Safely Things Beginners Get Wrong sheet.getLastRowNum() returns the index of the last row, not the count; blank rows in between are skipped by the for-each ...

Create Styles Once, Reuse Everywhere Practical Tips A workbook supports ~64,000 styles — create each style once and reuse the object, never one style per cell. ...

Writing Formulas Notes Formulas use English function names with commas ( SUM(A1:A10) ) regardless of the Excel locale. Call evaluator.evaluateAll() before saving if downstream ...

The Problem XSSFWorkbook keeps the whole workbook in memory — a million-row export easily needs gigabytes of heap. SXSSFWorkbook keeps only a sliding window (default 100 rows) and ...

Reading a .docx File Writing a .docx File Full runnable version: ReadWordExample in the poi-examples repo. (Old binary .doc needs the separate poi-scratchpad artefact — prefer ...

Checklist Before Shipping Close everything with try-with-resources ( Workbook , streams). On Windows an unclosed stream locks the file. Reuse styles — the 64k style limit is per ...