If you don't want to use PersistenceUnit, lookup EntityManager in each request,
or inject it into a SLSB. But if you want to use EntityManager in a servlet, you
need to use UserTransaction to determine transaction boundaries.
HTH,
-marina
Felipe Gaúcho wrote:
> the persistenceunit is really necessary ? I really don't want to
> handle transactions by my own.. I prefer the container to do
> that....... (in general)..
>
> On Fri, Aug 14, 2009 at 11:34 PM, Martin Gainty<mgainty_at_hotmail.com> wrote:
>
>>you can't use @PersistenceContext to inject an EntityManager
>>
>>so you'll need to use @PersistenceUnit to inject an EntityManagerFactory
>>and use lookup to PersistenceUnit to get hold of an EntityManager
>>
>>EntityManagerFactory example:
>>
>>public class RegistrationServlet extends HttpServlet {
>>// inject EntityManagerfactory
>> @javax.persistence.PersistenceUnit private EntityManagerFactory emf;
>> @Resource private UserTransaction utx;
>> public void service ( HttpServletRequest req , HttpServletResponse resp)
>>throws ServletException, IOException {
>>
>> EntityManager em = emf.createEntityManager();
>> try {
>> ...
>>
>> utx.begin();
>> em.persist(credential);
>> utx.commit();
>>
>> ...
>>
>> } catch (Exception e)
>> {
>> try {
>> utx.rollback();
>> } catch (Exception e) {}
>>
>> }
>> finally
>> {
>> em.close();
>> }
>> }
>>
>>or
>>declare a dependency on an EntityManager from web.xml
>>
>> < persistence-context-ref>
>> < persistence-context-ref-name>
>> persistence/LogicalName
>> </persistence-context-ref>
>> < persistence-unit-name>
>> ActualPUNameAsItAppearsInPersistence.xml
>> </persistence-unit-name>
>></persistence-context-ref>
>>
>>then use JNDI to lookup
>>
>>public class RegistrationServlet extends HttpServlet {
>>
>> @Resource private UserTransaction utx;
>>
>> public void service ( HttpServletRequest req , HttpServletResponse resp)
>>
>> throws ServletException, IOException {
>>
>> Context envCtx = InitialContext().lookup("java:comp/env");
>>
>> EntityManager em = (EntityManager)
>>envCtx.lookup("persistence/LogicalName");
>> ...
>>//start transaction
>> utx.begin();
>>//persist credential to DB
>> em.persist(credential);
>>//commit data
>> utx.commit();
>> ...
>>
>> }
>>}
>>http://weblogs.java.net/blog/ss141213/archive/2005/12/dont_use_persis_1.html
>>
>>Martin Gainty
>>______________________________________________
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>>
>>
>>>Date: Fri, 14 Aug 2009 20:22:16 +0200
>>>From: fgaucho_at_gmail.com
>>>To: users_at_glassfish.dev.java.net
>>>Subject: Re: how to create a MySql datasource using asadmin ?
>>>
>>>so, this code is thread safe:
>>>
>>>@PersistenceUnit(name = "footprint")
>>>private EntityManagerFactory emf;
>>>
>>>public T read(final Serializable primaryKey) throws Exception {
>>>EntityManager manager = emf.createEntityManager();
>>>try {
>>>return manager.find(entityClass, primaryKey);
>>>} finally {
>>>manager.close();
>>>}
>>>}
>>>
>>>
>>>??
>>>
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>>>
>>
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