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From tornike <torni...@gmail.com>
Subject Re: EntityManager & Servlets
Date Tue, 15 Sep 2009 20:39:50 GMT

Thanks for replying to my question.
I have figured out how EJB works with servlets now, I am not a very
experienced developer and I learn through examples. I inject session beans
(@EJB) into my servlets and database manupulations are kept in session
beans.
While reading about these issues I came across Java 6EE where as I
understood EJBs are introduced in web container as web beans. Should be
easier to figure out for newcomers like me:)
Thanks


Jay D. McHugh-3 wrote:
> 
> Sorry for the late reply to this.
> 
> Geronimo should not allow you to add container managed entity managers
> to servlets.  They would not be thread safe.
> 
> I haven't looked at the example in a while - but I believe it is using a
> stateless session bean to access the entity manager.  That is perfectly
> acceptable (and correct)...
> 
> I just took a look at the example and it does in fact use a stateless
> bean (AccountBean).  So, that is why it is able to use container managed
> persistence.
> 
> I don't think that it would actually make projects simpler to move the
> data access logic into each of the servlets that need it.  For me at
> least, centralizing the logic into session beans means that I am forced
> to consider exactly what I will be doing with the data and only write
> the code once to do it.
> 
> Hope that helps,
> 
> Jay
> 
> tornike wrote:
>> Yes, but if it's in their example maybe it's OK for Geronimo to use
>> container
>> managed EntityManager with the servlet and there won't be any threading
>> issues. If it's true then we wouldn't need any EJB's in the project and
>> simply communicate to JPA entities even when using container managed
>> EntityManager. As far as I know this method is discouraged but if it's ok
>> to
>> do in Geronimo it would greatly simplify many projects. 
>> 
>> 
>> 
>> Fredrik Jonson-3 wrote:
>>> In <25221488.post@talk.nabble.com> tornike wrote:
>>>
>>>>  EntityManager is not thread safe and it should not be injected into
>>>> the
>>>>  servlet. (container managed one) However in the example of ejb-JPA 
>>>>
>>>> http://cwiki.apache.org/GMOxDOC21/container-managed-persistence-with-jpa.html
>>>>
>>>>  I have tested the example works without problems so are there
>>>> conditions
>>>>  when it can be done or am I understanding it the wrong way?
>>> I'd say the example is wrong or at least careless. So I'm also
>>> interested
>>> if someone thinks otherwise.
>>>
>>> If I would have done it I'd inject a EntityManagerFactory in the servlet
>>> and
>>> acquired a new EntityManager from the pool for each request to doGet
>>> method:
>>>
>>> public class Example extends HttpServlet {
>>>   @PersistenceUnit
>>>   private EntityManagerFactory emf;
>>>
>>>   @Override
>>>   protected void doGet(HttpServletRequest request, HttpServletResponse
>>> response)
>>>     throws ServletException, IOException {
>>>       EntityManager em = emf.createEntityManager();
>>>       // do stuff
>>>
>>> -- 
>>> Fredrik Jonson
>>>
>>>
>>>
>> 
> 
> 

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