Spring Boot

Goal

Everything a backend engineer needs to build, secure, test, observe, and ship production Spring Boot services — from how auto-configuration actually decides which beans to create to REST APIs, Spring Data JPA, transactions, security, messaging, caching, resilience, native images, and containerized deployment. Concept-first and interview-grade: every module teaches you to justify a choice, name the failure mode, and mitigate it — not just recite what an annotation does. Pairs with the Java language fundamentals and with Gen AI Engineer when you build AI features on the JVM (via Spring AI, the Spring-idiomatic client for LLM providers — not yet its own track in this vault).

How to use this track

You don’t master Spring Boot by memorizing annotations — you master it by understanding the container underneath them and the auto-configuration that wires it. Go top-to-bottom for a full pass, or jump to the module you need. Every module follows the same through-line: concept → how it works internally → trade-offs & alternatives → gotchas (shown failing) → mitigations → best practice → in practice → sources.

The through-line every module answers

What it is → the trade-offs → when NOT to use it → the failure mode → the committed recommendation. That is exactly what a senior Spring interview probes: not “what is @Transactional” but “what happens when you call a @Transactional method from within the same class, and why.”

Versions here are HIGH-CHURN — re-verify before relying on them

This track is written against Spring Boot 4.1.x on Spring Framework 7.0, Jakarta EE 11 (Tomcat 11, Hibernate ORM 7, Hibernate Validator 9), Jackson 3, JUnit 6, with a JDK 17 baseline (Java 21/25 recommended). Spring Boot 4.0 went GA on 2025-11-20. The concepts (IoC, the bean lifecycle, the filter chain, transaction propagation, the N+1 problem) are durable; the coordinates (version numbers, property keys, deprecations like RestTemplate) move every release. Each module flags its volatile facts — check them against the primary docs. Today’s date context: mid-2026.

Three concerns that run through EVERY module (the spine)

1. Auto-configuration & “convention over configuration” — Boot’s defining trait. You must know what it auto-configures and how to override or disable it, or you’ll fight the framework. See 01 - Spring Boot Fundamentals & Auto-Configuration.
2. The container & bean lifecycle — everything is a bean; DI, scopes, and proxies underlie transactions, security, caching, and @Async. Half of “why doesn’t my annotation work?” is a proxy/self-invocation issue. See 02 - IoC Container, Beans & Dependency Injection.
3. Production-readiness — security, observability, resilience, and graceful shutdown are not afterthoughts; they are covered as first-class modules (08 - Spring Security, 12 - Actuator, Metrics & Observability, 13 - Resilience & Production Readiness).

Curriculum

Suggested order

Foundations (01–03) → Web (04–05) → Data (06–07) → Cross-cutting (08–10) → Quality & operations (11–13) → Ship it (14–15). If you only do six before an interview: 01, 02, 06, 07, 08, 12 — the container, persistence, transactions, security, and observability are where senior questions concentrate and where production incidents actually come from.

How this fits the rest of the vault

JAVA LANGUAGE + JVM                    the language, memory model, concurrency
        +
SPRING FRAMEWORK (core)                IoC container, AOP, the bean model
        ▼
SPRING BOOT (this track)               auto-configuration, starters, the
                                       production-ready opinionated stack
        +
SPRING DATA / SECURITY / etc.          the ecosystem modules layered on top
        ▼
SPRING AI  ───────────────────────►    building LLM features on the JVM
                                       (bridges to [[00 - Gen AI Engineer Index]])

Spring Boot is Spring Framework with opinions: the container, DI, and AOP are Framework; the auto-configuration, starters, embedded server, and Actuator are Boot. Keeping that line straight is itself an interview signal.

Anchor sources (re-verify — they move every release)

• Spring Boot reference: docs.spring.io/spring-boot · Spring Boot 4.0 Release Notes · Spring Boot 4.0.0 announcement
• Spring Framework: reference docs · Framework 7.0 GA
• Ecosystem: Spring Data JPA · Spring Security · Micrometer · Testcontainers
• HTTP clients direction: The state of HTTP clients in Spring (2025)

On the diagrams

Animated GIFs are generated by assets/gen_springboot_gifs.py (Pillow, via the animated-diagrams skill engine). Re-run it to tweak a figure. Obsidian animates GIFs in reading view (animated SVG renders frozen and Mermaid is static, so GIF is used for anything that moves).