Spring Boot 3 EOL to Spring Boot 4: A Production Upgrade Playbook (Including Jackson 2 to 3)

This article provides a practical, phased migration strategy from Spring Boot 3.x to Spring Boot 4.0, emphasizing end-of-life (EOL) risks, CVE exposure, and Jackson 2 to Jackson 3 migration. It covers platform baseline changes (Java/Jakarta/Servlet), dependency restructuring, test infrastructure updates, and security considerations. The playbook includes a three-phase approach: stabilizing on latest 3.5.x, migrating to 4.0 with compatibility bridges, and converging to native 4.0 patterns. It also addresses companion migrations for Spring Modulith 2.0 and Testcontainers 2.x, along with a production rollout checklist and CI/CD gates. Targeted at developers and DevOps teams managing Spring Boot upgrades in production environments.