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From "Altenhof, David Aron" <dalte...@iupui.edu>
Subject RE: Interceptor attempt
Date Thu, 11 Nov 2010 14:33:46 GMT
Greg-

Thanks for bumping my memory on when the page gets rendered. I remember reading that somewhere,
but forgot when writing this. Committing the transaction in the action for save/delete seems
to be the way to go.  

Regarding ThreadLocal, I'm a bit new to Java and still struggling a bit with the concept.
You can simply simply call a sf.getCurrentSession().beginTransaction(); to begin and  sf.getCurrentSession().getTransaction().commit();
to commit it from anywhere in your app?

Thanks,

David



-----Original Message-----
From: Greg Lindholm [mailto:greg.lindholm@gmail.com] 
Sent: Wednesday, November 10, 2010 5:15 PM
To: Struts Users Mailing List
Subject: Re: Interceptor attempt

(Sorry - premature post)

Hi David,

I've written a couple of these so let me give you some advice:

Create an Interface "HibernateAware" that your actions will implement if they want a Hibernate
Session and Transaction injected.

public interface HibernateAware
{
 void setSession(Session session);
 void setTransaction(Transaction tx);
}

Next, you only want to create a Session and Transaction if the Action implements HibernateAware,

Object action = invocation.getAction();
if (action instanceof HibernateAware)
{
  HibernateAware ha = (HibernateAware) action;
  ha.setSession(...)
  ha.setTransaction(...)
 ...
}
else
{
return invocation.invoke();
}


Next and a bigger issue;  I think it is a really bad idea to do the commit in the interceptor.
 If the commit fails it is too late to tell the user or do anything about it since your result
and response has already been rendered.  You need to understand how the interceptor stack
works, but the key point is the first interceptor or action that returns a result string causes
the result to be processed and the response (jsp page) to be rendered before the interceptor
stack starts to unwind. SO if the commit fails, it's too late in the interceptor to do anything
about it, you have already rendered the everything is OK page to the user.

What I do is to commit the transaction in the Action then if it fails I can return a FAILURE
result.

Now if you need a Transaction open in order to allow lazy loading while rendering the jsp
page what I will do is begin a second transaction.

Then in the interceptor I will Rollback the transaction and close the session since nothing
in the page rendering should modify any entities.

Next; your interceptor needs to close the session.

Your option instead of storing the session in the action is to store it and the transaction
in ThreadLocal storage. In fact if you copied your HIbernateUtil from many of the examples
it may already be storing the session in ThreadLocal storage as this is very common.

One thing you need to be aware of regarding ThreadLocal storage and web servers; most web
servers use a thread pool for executing requests and once your request is finished the thread
gets put back into the pool for use on a future request.  This can be a problem if you don't
properly clean up all ThreadLocal storage, for example if you leave a session open and in
ThreadLocal storage when the thread gets re-used for the next request it will already have
a session in it and it will be reused.  This usually happens when an exception occurs and
the session doesn't get closed so chances are the session is corrupt or dead which will cause
this later request to fail unexpectedly.

I would put the call to invocation.action() in a try block with a finally block that closes
the session and cleans up any other THreadLocal stuff you have so it doesn't pollute the thread
pool.




On Wed, Nov 10, 2010 at 4:44 PM, Greg Lindholm <greg.lindholm@gmail.com> wrote:
> Hi David,
>
> I've written a couple of these so let me give you some advice:
>
> Create an Interface "HibernateAware" that your actions will implement 
> if they want a Hibernate Session and Transaction injected.
>
> public interface HibernateAware
> {
>
> }
>
> On Wed, Nov 10, 2010 at 3:45 PM, Altenhof, David Aron 
> <daltenho@iupui.edu> wrote:
>> Hello all, I'm trying to write my own interceptor, and have a question or two...
>>
>> I'd like to write a simple interceptor that will manage hibernate sessions for me.
I know that there are more sophisticated ways to do this using Spring, etc. but this is mainly
a learning experience.
>>
>> So, given the simple code below, my questions are:
>>
>>
>> 1)      Does it appear to be thread-safe?
>>
>> 2)      Is there any condition, other than an unhandled exception elsewhere in
the app, that would cause the transaction not to be committed?
>>
>> 3)      Are there any better places to stash the session and transaction references
other than the Action? I tried putting it on the value stack, but that wreaked havoc with
the Params interceptor.
>>
>> Thanks!
>>
>> David
>>
>> public class HibernateInterceptor implements Interceptor {
>>
>>                public String intercept(ActionInvocation 
>> actionInvocation) throws Exception {
>>
>>                                Session sess = 
>> HibernateUtil.getSession();
>>                                Transaction tx = 
>> sess.beginTransaction();
>>
>>                                // Put sess, tx in Action
>>                                Action action = (Action) 
>> actionInvocation.getAction();
>>                                if(action instanceof MyAction ) {
>>                                                
>> ((MyAction)action).setHibSession(sess);
>>                                                
>> ((MyAction)action).setHibTransaction(tx);
>>                                }
>>
>>                                String rslt = 
>> actionInvocation.invoke();
>>
>>                                try {
>>                                                // Try to
commit:
>>                                                tx.commit();
>>
>>                                } catch (Exception ex) {
>>                                                // Try to
rollback and do other stuff here ...
>>                                }
>>                                return rslt;
>>                }
>>                public void destroy() {}
>>                public void init() {}
>> }
>>
>>
>

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