Java/Spring engineering notes built on top of 10+ years in telecom BSS and network provisioning, before I moved into microservices architecture. This isn't a general-purpose dev encyclopedia — it used to try to be one and it was worse for it. What's left is what I can actually back up in a conversation: architecture decisions, failures, debugging recipes, and a telecom domain guide built from things like number portability and a Nokia-to-Huawei core migration, not from reading Wikipedia.

I used to run a second repo, dev-library, for everything more generalist — languages, web fundamentals, cloud, AI. It quietly grew into a parallel copy of the same subjects covered here, just less maintained. I folded it into this one in July 2026 (with its Git history intact — see docs/governance/migration-map.md if you want the full reasoning) instead of keeping two half-finished libraries alive.

If you want to learn how something works in general, start in foundations/. If you want to know how to actually build, run, or fix it with this stack, that's knowledge/. Runnable code lives in projects/, graded from a ten-line CLI up to a multi-service platform.

engineering-library/
├── projects/                  nano → micro → mini → standard → macro Java/Spring/Angular projects
├── knowledge/                  choosing, building, operating, debugging — this stack, in production
│   ├── telecom/                BSS/OSS, provisioning, 5G core, number portability, roaming
│   ├── backend/                Java/Spring, Node.js, microservices, APIs
│   ├── architecture-library/   architecture patterns and ADRs
│   ├── engineering-failures/   postmortems and things that broke, written up honestly
│   ├── debugging-recipes/      how I actually tracked down specific bugs
│   ├── database-engineering/   Postgres/Oracle, schema and query design
│   ├── security-patterns/      auth, SSO, API security patterns
│   ├── devsecops/              CI/CD, pipeline security
│   ├── ai-engineering/         RAG, agents, evals, hooks/skills, model routing and cost
│   ├── cybersecurity/          offense/defense fundamentals, pentest methodology, blue team
│   ├── code-review/            reviewing and being reviewed
│   └── practices/              testing, git workflows, agile
├── foundations/                 languages, web, cloud, mobile, and other generalist ground
└── docs/standards/             Java/Spring, Angular, SQL, security conventions I hold projects to

Each knowledge/ folder has its own README, and the ones that started here also carry a _TEMPLATE.md so new entries stay consistent. Entries get added as I actually hit the thing, not in batches — some folders are thinner than others and that's honest, not an oversight.

Most Java/Spring content online comes from people who've only ever worked in web/e-commerce backends. knowledge/telecom/ is the opposite: number portability modeled as a multi-operator state machine, a real 5G core migration, provisioning architecture that has to survive a partner network being down. It's the one section of this repo nobody else can really write.

MIT — see LICENSE.