feat(build): upgrade platform baseline to Java 21 and Spring Boot 4

Problem to solve

A major version is the only reasonable moment to change the baseline. Java 21 brings virtual threads, and Spring Boot 4, available since November 2025, is the line that will receive support through AWE 5's lifetime. This is also the moment to realign Selenium 4.18 with the BOM, upgrade java-jwt from 3.18 to 4.x, and remove the Lombok plugin patch.

Further details

Impact on existing AWE 4 products (level 3 - High): every project will have to upgrade its JDK and Spring Boot version; there is no shortcut. This is mitigated with a dedicated migration guide, maintenance of the 4.x branch with security fixes for a defined period, and a 5.x archetype available from day one.

Effort: L (1-3 weeks) Delivery phase: 2 (major version, controlled breakage) Development order: 28 (Block 3 - Backend; closes the major version)

Proposal

  • Set Java 21 as the minimum supported version
  • Upgrade to Spring Boot 4 and Spring Framework 7
  • Make virtual threads activatable via a property
  • Review pinned dependencies in awe-dependencies and the starters
  • Realign Selenium to 4.18+ per the Spring Boot BOM
  • Upgrade java-jwt from 3.18 to 4.x
  • Remove the Lombok plugin patch

What does success look like, and how can we measure that?

  • The framework builds and all test suites pass on Java 21 with Spring Boot 4 / Spring Framework 7
  • Virtual threads can be enabled via a configuration property without code changes
  • A dedicated 4-to-5 migration guide covering the JDK/Boot jump is published
  • A 5.x archetype is available and builds a working sample project
  • support/4.x continues to receive security fixes per the published support window

Links / references

  • Depends on: #762 (closed), #764
  • Part of the AWE 5 evolution plan (initiative 12 of 27, development order 28).