Upgrade Java 8 → 21

Java 8 LTS support ended for many vendors; Java 11, 17, 21 are the LTS waypoints. The 8 → 21 jump unlocks records, virtual threads, pattern matching — language features that meaningfully improve code. The trade-off: dependency upgrades (Spring Boot 2 → 3, Hibernate 5 → 6) ride along.

When to use

• Codebase still on Java 8 (yes, this is common in 2026).
• Considering 8 → 11 or 11 → 17 — same pattern; less benefit.
• Greenfield modules that should be 21 from the start.

When NOT to use

• Stuck on a vendored Java 8 by customer requirement (regulated, embedded).
• Using libraries that explicitly don't support 17+ (rare; usually a fork exists).
• Java 8 with Spring Boot 1.x — multiple sequential upgrades (Spring Boot 1 → 2 → 3 + Java 8 → 21). Stage carefully.

The waypoints