What is Jakarta EE 11 and what changes does it bring in Spring Boot 4?

// All javax.* imports from Spring Boot 2.x are gone in Boot 4
// They must be jakarta.* (this was also true in Boot 3 but Boot 4 enforces it)

// WRONG (will not compile in Boot 4):
import javax.persistence.Entity;
import javax.validation.constraints.NotNull;
import javax.servlet.http.HttpServletRequest;

// CORRECT:
import jakarta.persistence.Entity;
import jakarta.validation.constraints.NotNull;
import jakarta.servlet.http.HttpServletRequest;

// The OpenRewrite recipe handles automated migration:
// Migrate_To_Jakarta_EE_10 recipe covers remaining javax.* -> jakarta.*

// Hibernate 7.1 breaking change: detached entities
// Boot 3: silently reassociated (lenient)
// Boot 4: throws exception if you try to persist a detached entity without explicit merge
@Transactional
public void updateOrder(Order detachedOrder) {
    // Boot 3: orderRepo.save(detachedOrder) might silently merge
    // Boot 4: be explicit:
    orderRepo.save(entityManager.merge(detachedOrder));
}