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Re: Why save the EntityManagerFactory

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On 19/08/2015 11:32, Cecil Westerhof wrote:
> I am using http://www.uow.edu.au/~nabg/399/JPA/JPA.pdf to get a start
> with JPA. When looking at page 14 an EntityManagerFactory is created
> and kept until the end of the program.
> Could the following:
>      emf = Persistence.createEntityManagerFactory("JavaApplication12PU");
>      em = emf.createEntityManager();
> not just be changed to:
>      em = Persistence.createEntityManagerFactory("JavaApplication12PU").createEntityManager();
>

Just a guess but

private static void closedownDataPersistence() {
    em.close();
    emf.close();
}

implies to me that both em and emf consume system resources and require
separately closing to release those resources when you are finished with 
them.

em = 
Persistence.createEntityManagerFactory("JavaApplication12PU").createEntityManager(); 
might leave an unclosed 'thing' consuming resources.

What is the status of the EntityManagerFactory when you return from your 
chained expression above? you certainly must create one but when you 
return you have no reference to the factory so can't close it. It won't 
be collected as, if it still has a handle on some system resource it 
won't be null. So you are left with a zombie Object consuming resources 
with no way to reclaim it.

Also, long chains of method calls are harder to read so it's good 
practice to unchain them. Chaining isn't particularly clever although as 
they become more adept at the language all Java developers seem to do it 
to some extent or other.

Like I say, just a guess.


-- 
Laughing Spam Fritter

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Thread

Why save the EntityManagerFactory Cecil Westerhof <Cecil@decebal.nl> - 2015-08-19 12:32 +0200
  Re: Why save the EntityManagerFactory Arne Vajhøj <arne@vajhoej.dk> - 2015-08-19 19:15 -0400
  Re: Why save the EntityManagerFactory Eternal Hope <laughingspam99@gmail.com> - 2015-08-21 09:43 +0100
    Re: Why save the EntityManagerFactory Arne Vajhøj <arne@vajhoej.dk> - 2015-08-30 21:55 -0400
      Re: Why save the EntityManagerFactory Lew <lewbloch@gmail.com> - 2015-08-31 10:13 -0700

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