EntityManager являетсяnot thread-safe по определению. Спецификация сервлетов говорит, что в нераспределенной среде и без реализацииSingleThreadModel, естьonly one servlet instance per definition.

Поэтому в Java EE, когда вы вводитеEntityManager сквозь@PersistenceContext в поле сервлета - это не потокобезопасно:

<code>public class MyServlet extends HttpServlet {

    // Not thread-safe, should be using EMF instead.
    @PersistenceContext
    private EntityManager em;
}
</code>

Is this correct to say that even though the default scope of Spring beans is singleton, the EntityManager is thread-safe as the Spring uses ThreadLocal to bind its transaction and EntityManager to it?

Is the above Servlets example still valid in Spring? Is it still not thread-safe?

Does the ThreadLocal approach works only for Spring managed beans and plain servlet is not one of those?

As far as I remember, it's the container responsibility to inject the EntityManager. In Glassfish Java EE implementation, it was the application server who discovers the @PersistenceContext as injection point.
How does it look like in Spring? Is the Spring Framework responsible for discovering those annotations or it's responsibility of the JPA implementor?