What is the javax to jakarta namespace migration in Spring Boot 3, and why did it happen?

Spring Boot 3 & Modern Java

Spring Boot 3 (and Spring Framework 6) require Jakarta EE 9+ APIs, meaning every enterprise Java API package Spring depends on — servlets, JPA, Bean Validation — moved from the `javax.*` namespace to `jakarta.*` (e.g., `javax.persistence.Entity` became `jakarta.persistence.Entity`). This happened because Oracle transferred Java EE to the Eclipse Foundation (renamed Jakarta EE), but retained trademark control over the `javax.*` package prefix, forcing the newly-independent Jakarta EE specifications to adopt a new namespace going forward.