[TASK] Lunch and Learn — Devoxx Belgium 2025: Java 21→25 in the dotCMS codebase

Description

Show-and-tell of the material I brought back from Devoxx Belgium 2025, delivered as a Lunch and Learn.

Scope change: the original topic on this issue was Memory Leaks. After reviewing the sessions I attended, the talk has been re-scoped to Java 21 → 25 and what it means for the dotCMS codebase, which is far more actionable for the team now that core compiles to Java 25 (parent/pom.xml → dotcms.core.compiler.release=25). Memory-related content survives as the GC segment (topic 4), not as a standalone leak-hunting talk.

Talk structure

Four topics, each split between two speakers: one presents the Java language/runtime concept, the other presents how it lands in the dotCMS codebase — with real examples from core, an explicit when it is a good idea and when it is not, and the adoption implications.

My part

The dotCMS half of each topic. Not slideware — every claim is backed by code in this repository:

• Concrete examples in the core codebase for each concept.
• When to adopt and when not to, grounded in constraints we have actually hit (Velocity introspection, Jackson round-trips, OSGi/plugin ABI stability, existing Immutables-based modelling).
• Implications of adoption: source vs binary compatibility, serialization contracts, plugin extensibility, test and benchmark needs.

Deliverable: a PR against this issue carrying the example code and the accompanying write-up.

Acceptance Criteria

• Prep and get good material to rock an awesome presentation
• Topic 1 — Three Amigos: dotCMS examples + adopt/do-not-adopt guidance
• Topic 2 — Java 21→25 APIs: dotCMS examples + adopt/do-not-adopt guidance
• Topic 3 — Loom: dotCMS examples + adopt/do-not-adopt guidance
• Topic 4 — GC: dotCMS baseline, candidate experiments, observability
• PR opened and linked to this issue

Priority

None

Additional Context

Baseline of the codebase as of this update, which is what makes the dotCMS half worth presenting:

• Core compiles to Java 25, so all of the above is available today with no version gate.
• sealed: zero usages anywhere in dotCMS/src/main/java.
• record: 15 declarations across 12 files, nearly all of them in the vendor-neutral search layer.
• The codebase models immutable data with Immutables (@Value.Immutable), so for this team the real question is Immutables vs records and open vs sealed hierarchies — not POJO vs record.