On Jan 20, 2012, at 4:51 PM, David Blevins wrote:
> I don't have a good vision for how separating them would be done, but I wonder if it's just as simple as having a "Transaction" interceptor and a "RollbackOnException" interceptor. Or some variation on the idea.
This idea came to me as a self-documenting and very flexible possible approach:
@Transactional
@Rollback({RuntimeException.class, MyCustomException.class})
public void doSomething() {
//...
}
If the exception is assignable to anything in the list, the transaction is rolled back. At this point there isn't the need for @ApplicationException or anything similar. Just about anyone could look at that and know what's going on and how to alter the behavior.
That's probably good enough right there.
In the future if we get some generally applicable pattern for annotation reuse in place (e.g. meta-annotations, more generic version of stereotype, whatever want to call it), these common combinations can be easily reused:
@Transactional
@Rollback({RuntimeException.class, MyCustomException.class})
@RolesAllowed({"Manager", "Admin"})
@Metatype
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface AcmeTransactionalOperation {
}
Then..
@AcmeTransactionalOperation
public void doSomething() {
//...
}
Effectively, the problem of what we need to squish together for convenience isn't our problem anymore. We just focus on clear and separate concerns. With some ability to compose things together, the question of "will users also want x with y" where the answer is clearly "sometimes" becomes an easy one for users to solve for themselves.
At that point we as spec designers need to only ask "will users want x and possibly not y". And of course, there'd be some flexibility to get that answer wrong. If we learn annotation X encompasses too much functionality (the "i got more than I wanted" problem), we could of course split those concerns into annotations D and E then redefine X as a meta-annotation comprised of D and E.
-David
> I can see concrete use cases for people wanting the protection of MANDATORY and having the mindset of, "Look, it's your transaction, deal with the exceptions as you see fit. Don't make me tell you what's safe and isn't."
>
> Of course the concept of app/system exceptions could still be supported for when people opt-into the "RollbackOnException" contract, though I wonder if it would be all that used. Theoretically, if you had specific goals for your exception handling, you could simply assume that responsibility. Don't use the standard "RollbackOnException" interceptor and instead write your own interceptor to call setRollbackOnly() using whatever conditions you wanted. With things separated, you'd have this ability, with them "smushed" together you'd have to write all your own transaction handling code.
>
> A lot of things can simply be traced back to the fact that interceptors did not exist when these particular APIs were created.
>
> For as large as the CMT API is it's actually not that complete. For example, why not an interceptor that calls getRollbackOnly() and throws a "DontBotherInvokingMeException" if the answer is false? Was probably not worth the xml before and perhaps not worth annotation now, but it's an interesting omission.
>
>> I definitely agree with you about the SFSB destruction issue flagged
>> in your blog. I would advocate that we try to fix that for the
>> transactional interceptor case. We could try to fix it in general
>> with the introduction of more metadata, if the EJB EG wants.
>
> Will definitely give that some thought.
>
>>
>>>
>>> Not a proposal, but some thoughts.
>>>
>>
>> thanks again for posting
>
> Thanks for tackling this topic. It's a fun one. We could certainly green-light the CMT API as-as with no harm, but there's no denying we won't get this chance again for quite a long time :)
>
>
> -David
>
>>>>
>>>> Jan 18, 2012 07:53:44 PM, jsr342-experts_at_javaee-spec.java.net wrote:
>>>> Supporting a superset of Spring and EJB would result in something
>>>> very complex. In particular, the way Spring allows control over
>>>> the rollback behavior using include lists and exclude lists and
>>>> class names and Class objects is very complex. We were hoping to
>>>> satisfy most developers with something much simpler than Spring
>>>> or EJB.
>>>>
>>>> Which of the features from Spring's @Transactional annotation do you
>>>> think are the most used?
>>>>
>>>> reza_rahman_at_lycos.com wrote on 01/17/12 09:47:
>>>>> Sorry for the delay in responding. Things are hectic these days...
>>>>>
>>>>> I actually think EJB 3 application vs. system exception is a good idea (except
>>>>> for that I don't think the special treatment of RemoteException is really needed
>>>>> -- in Spring, system exception == runtime exception). It's easy to explain,
>>>>> works in the real world and corresponds nicely with exception handling best
>>>>> practices: http://onjava.com/pub/a/onjava/2003/11/19/exceptions.html?page=1.
>>>>> Now, I do think it would be very useful to provide a mechanism to override
>>>>> default exception level behavior (no
>>>>> annotation/checked/unchecked/_at_ApplicationException) per bean/method. Basically,
>>>>> I would like to see the super-set of Spring
>>>>> (http://static.springsource.org/spring/docs/2.0.x/api/org/springframework/transaction/annotation/Transactional.html)
>>>>> and EJB exception handling.
>>>>>
>>>>> As to wrapping exceptions, I do agree it's completely overkill and
>>>>> counter-intuitive (Spring does not do it, for example).
>>>>>
>>>>> Hope it helps.
>>>>>
>>>>> Jan 10, 2012 03:14:50 PM, jsr342-experts_at_javaee-spec.java.net
>>>>> <mailto:jsr342-experts_at_javaee-spec.java.net> wrote:
>>>>>
>>>>>
>>>>> It looks like we're in general agreement on the transactional interceptor
>>>>> approach I proposed earlier.
>>>>>
>>>>> Aside from the more obvious open issues around naming, there is an
>>>>> issue related to the handling of exceptions that we need to resolve.
>>>>>
>>>>> The issue relates to what should happen with regard to the state of a
>>>>> transaction when an exception is thrown that reaches a transactional
>>>>> interceptor.
>>>>>
>>>>>
>>>>> First, some background on how EJB handles container-managed transactions....
>>>>>
>>>>> The EJB spec distinguishes between "system exceptions", which
>>>>> cause the container to mark the transaction for rollback, and
>>>>> "application exceptions", which by default do not cause the
>>>>> transaction to be marked for rollback.
>>>>>
>>>>> An application exception is either a checked exception (other than the
>>>>> RemoteException) or a runtime exception annotated with @ApplicationException.
>>>>>
>>>>> @Target(TYPE) @Retention(RUNTIME)
>>>>> public @interface ApplicationException {
>>>>>
>>>>> /**
>>>>> * Indicates whether the container should cause the transaction to
>>>>> * rollback when the exception is thrown.
>>>>> */
>>>>> boolean rollback() default false;
>>>>>
>>>>> /**
>>>>> * Indicates whether the application exception designation should
>>>>> * apply to subclasses of the annotated exception class.
>>>>> */
>>>>> boolean inherited() default true;
>>>>> }
>>>>>
>>>>>
>>>>> An EJB system exception is a subclass of RemoteException or a subclass
>>>>> of RuntimeException that has not been designated as an application
>>>>> exception.
>>>>>
>>>>> When the EJB container intercepts a system exception (at a business
>>>>> method boundary), it causes the current transaction to be marked for
>>>>> rollback. When the called method runs in the context of the caller's
>>>>> transaction, the container throws the EJBTransactionRolledBackException
>>>>> (or some variant thereof). If a new transaction was *started* for the
>>>>> called method, the container throws the EJBException. In both these
>>>>> cases, the original exception is wrappered. Application exceptions
>>>>> are thrown back to the caller as is.
>>>>>
>>>>> If the caller receives an application exception, the caller presumably
>>>>> knows based on the exception type whether the exception causes
>>>>> rollback or not. Unless the caller is familiar with the transaction
>>>>> attribute of the called method, however, the caller doesn't know
>>>>> whether its own transaction was marked for rollback or whether only
>>>>> the callee's transaction was rolled back. However, the caller can
>>>>> invoke the getRollbackOnly method to determine the state of its own
>>>>> transaction.
>>>>>
>>>>> In the case of a system exception, if the caller receives the
>>>>> EJBException, the caller can assume that the callee's transaction was
>>>>> rolled back, but that the caller's own transaction was not affected.
>>>>> If the caller receives the EJBTransactionRolledBackException, the
>>>>> caller knows that its own transaction was marked for rollback (and
>>>>> that the callee was run within the context of that same transaction).
>>>>>
>>>>>
>>>>> So much for background.... Now, what should the behavior be for
>>>>> transactional interceptors?
>>>>>
>>>>> While we could adopt the EJB approach (modulo some renaming), Bill and
>>>>> I are concerned that it is too complex. (See Chapter 14 ("Exception
>>>>> Handling") of the EJB 3.1 spec for the gory details.)
>>>>>
>>>>> We propose a simpler approach along the following lines:
>>>>>
>>>>> By default, all exceptions should result in the current transaction
>>>>> being marked for rollback. If the developer believes that the
>>>>> exception should not cause rollback, he or she annotates the exception
>>>>> class with @DontRollbackTransaction (real name for this exception *TBD*).
>>>>>
>>>>> The DontRollbackTransaction annotation is simply:
>>>>>
>>>>> @Target(TYPE)
>>>>> @Retention(RUNTIME)
>>>>> @Inherited
>>>>> public @interface DontRollbackTransaction {}
>>>>>
>>>>> All exceptions are thrown back without any wrappering. While we can
>>>>> understand the rationale for wrappering an exception that marks the
>>>>> caller's transaction for rollback in a TransactionRolledbackException,
>>>>> we're not convinced that this is needed. Likewise, we're not
>>>>> convinced of the need to make a distinction by means of exception
>>>>> wrappering as to whether the callee's transaction was rolled back.
>>>>>
>>>>>
>>>>> We'd like your feedback on this and on your experience with regard
>>>>> to how developers are actually making use of the current EJB facility,
>>>>> particularly in view of the assumptions that we are making.
>>>>>
>>>>> Again, we are assuming the following:
>>>>>
>>>>> (1) It is not essential that the caller be able to identify from an
>>>>> exception that it receives whether its own transaction was marked
>>>>> for rollback, as the caller can use the getRollbackOnly method
>>>>> to determine this.
>>>>>
>>>>> (2) It is not essential that the caller be able to identify by means
>>>>> of the exception that it receives back whether a transaction
>>>>> was started on behalf of a method that it invoked, as it can
>>>>> use its knowledge of the exception received and getRollbackOnly
>>>>> status to determine this if it does not already know this information.
>>>>>
>>>>> (3) Subclasses of dont-rollback exceptions will typically be dont-rollback
>>>>> exceptions, and, if not, they can be defined to not extend dont-rollback
>>>>> exceptions. (Note that if we receive compelling feedback from
>>>>> developers to the contrary on this point, we could always add a
>>>>> an element to the annotation to control this at a later time. If
>>>>> we think this is at all likely, we should choose an annotation
>>>>> name accordingly.)
>>>>>
>>>>>
>>>>> Please post your feedback.
>>>>>
>>>>> Other specleads should feel free to forward this message to your expert
>>>>> groups for
>>>>> further input.
>>>>>
>>>>>
>>>>> thanks,
>>>>>
>>>>> -Linda
>>>>>
>>>>
>>>
>