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Add excel-export module: Apache POI 6.0.0 XSSF vs SXSSF under a fixed heap, 1,000,000 rows streamed with StreamingResponseBody, OpenCSV, sheet rolling, temp-file cleanup

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Co-Authored-By: Claude Sonnet 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_017ic4b4VQVEJWetTT1dYzyJ
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asmhatre
2026-10-29 06:18:42 +00:00
co-authored by Claude Sonnet 5.5
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# excel-export
Companion code for **[Export Excel and CSV from Spring Boot: Streaming 1 Million Rows with Apache POI SXSSF](https://ankurm.com/spring-boot-export-excel-csv-streaming-poi-sxssf/)**.
Spring Boot 4.1.2, Spring Framework 7, JDK 25, Apache POI 6.0.0 (`poi-ooxml`), OpenCSV 5.12.0. No database, no Docker.
| Piece | Code | What it shows |
|---|---|---|
| XSSF endpoint | `ExportController#xssf` | whole workbook in heap; the baseline that runs out of memory |
| SXSSF endpoint | `ExportController#sxssf` | `SXSSFWorkbook(100)` + `StreamingResponseBody`, `dispose()` in `finally`, optional `compressTempFiles` |
| CSV endpoint | `ExportController#csv`, `CsvExporter` | OpenCSV streaming, UTF-8 BOM for Excel, formula-injection guard, swallowed write errors |
| Writer shared by XSSF and SXSSF | `XlsxExporter` | styles created once, freeze pane, auto filter, lakh/crore number format, sheet rolling at 1,048,576 rows |
| Data | `SaleSource` | rows computed from their index (stands in for a database cursor) |
| Diagnostics | `ProbeController` | peak used heap and peak RSS; delete before shipping |
```bash
./scripts/run-all.sh # tests + every measurement; rewrites output/*.txt (15-25 minutes)
curl -o sales.xlsx 'http://localhost:8080/export/sxssf?rows=1000000' # after: java -jar target/excel-export-1.0.0.jar
```
`output/01..04` come from the tests, `output/05..09` from `scripts/measure.sh`, `output/10` from `scripts/libreoffice-check.sh`, which starts a fresh JVM with a fixed
`-Xmx` for every line. The numbers are indicative: they were taken on a shared 2-vCPU sandbox, one run per line.
Not run here: a real database cursor (rows are generated) and Microsoft Excel itself. LibreOffice 24.2.7.2 refuses to open
the SXSSF file because its ZIP entries carry a zero timestamp (same with POI 5.5.1); see `output/10-libreoffice.txt`.