Most production Java runs on 21, and will move next to 29. That means four releases of changes arriving in one upgrade. Java 26 shipped HTTP/3 in the standard HTTP client, faster startup, a free garbage collector improvement, and the first warnings in the plan to make final fields truly final. Here is what helps you, what will break your reflection-heavy libraries, and how to reduce the risk of an upgrade you have not started.
How to migrate a Spring Boot microservice fleet from Java 8 to Java 17 without downtime — the four layers, the order, the land mines, and the metric.