Is it safe to inject an EJB into a servlet as an instance variable?

Question

We all know that in the web tier there is the possibility that only a single instance of a given Servlet exists which services multiple requests. This can lead to threading issu

Answer 1

It's a mixed bag.

Stateless session beans may be injected and are safe. This is because even if a single instance of a stub is used, access to the methods will be serialized by the container.

I think what inferreddesign says is not true. It doesn't matter if the stateless session bean uses a persistence context. Only one caller will ever access a single bean instance at the same time, so even though the persistence context is not thread safe, the EJB guards against multiple access to it. Think of it as if every session bean method has the synchronized keyword applied to it.

The main problem with injecting an EJB in a Servlet I think is performance. The single stub instance will become a major area of contention when multiple requests are queuing up while waiting for a session bean method to be executed for them.