jafly by example

From Spring Boot to a connected enterprise architecture.

The canonical, build-it-yourself guide to jafly, the Java member of Framework by Firefly — a metaframework on top of Spring Boot (WebFlux · Project Reactor · R2DBC). You build one real application, a personal-loan origination service (Lumen Lending), from an empty folder to a secured, observable, event-driven, three-tier system — making every concept concrete before the next.

Published by the Firefly Software Foundation under Apache-2.0, in American English and Spain Spanish (es-ES).

What makes this book different

Every code listing in these pages is a verbatim slice of the companion Maven reactor under samples/lumen-lending, which is built and tested in CI. When prose drifts from working code, the build fails. What you read is what actually compiles and passes its tests.

Building the book

The book is a print-grade EPUB + PDF produced by a self-contained Python (WeasyPrint) pipeline.

# one-time
python3 -m venv build/.venv
./build/.venv/bin/pip install -r build/requirements.txt

# build (macOS — uses the DYLD shim for cairo/pango)
./build/run.sh --config book.yaml        # English  -> dist/firefly-java-by-example.{epub,pdf}
./build/run.sh --config book.es.yaml     # Spanish  -> dist/firefly-java-by-example-es.{epub,pdf}

# build (Linux / CI)
./build/build-book.sh --config book.yaml

Use JDK 25 for the companion application and verify that mvn -version reports that JDK. The published framework dependencies used by this sample target Java 25.

Verify the sample reactor, book tooling, and both editions’ listings:

mvn -f samples/lumen-lending/pom.xml verify
./build/.venv/bin/python -m pytest tests -q
./build/.venv/bin/python build/verify_code.py manuscript samples/lumen-lending
./build/.venv/bin/python build/verify_code.py manuscript-es samples/lumen-lending

Cover and interior artwork

The English and Spanish manifests select separate front and back covers from art/. PDF covers occupy the complete 7.5 × 9.25 inch trim page, without running headers or page numbers. EPUB editions include localized cover and back-cover documents at the beginning and end of the reading order, while retaining the chapter navigation. The interior uses the approved jafly logo on title and part pages, compact numbered chapter banners, and the shared paper, charcoal, amber and gold palette. Chapter titles come from the localized manifests when the manuscript does not supply a heading. Technical prose, diagram geometry, and verbatim listings are preserved.

The shared Framework by Firefly brand kit owns the cover design. Validate the checked-in outlined SVGs and 1500 × 1850 PNGs before rebuilding:

./build/.venv/bin/python build/gen_cover.py
# To import an updated canonical set:
./build/.venv/bin/python build/gen_cover.py --source /path/to/Framework-Brand-Kit/11-Books/java

On macOS, prefix these commands with DYLD_FALLBACK_LIBRARY_PATH="$(brew --prefix)/lib" if Cairo is not already on the loader path. The tool validates all four covers before copying them, and can rasterize missing PNGs from their outlined SVGs. It does not generate a new cover design. See artwork provenance for ownership and print boundaries.

Releases

The redesigned English and Spanish editions are published together as books-2026.10.08:

Edition	PDF	EPUB
English	Download PDF	Download EPUB
Español	Descargar PDF	Descargar EPUB

Book-only editions use a books-YYYY.MM.DD tag. The existing CalVer (vYY.MM.PATCH) workflow remains available for subsequent technical editions.

Scope

This book covers jafly, the Java family. The pyfly, larafly, rsfly and netfly frameworks, Firefly Agentic, the agentic-bridge and frontend projects have their own documentation and are outside this book's scope.

---

Copyright © 2026 Firefly Software Foundation. Licensed under Apache-2.0.