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From Simon Kitching <simon.kitch...@chello.at>
Subject Re: digester issue
Date Wed, 14 Nov 2007 16:02:45 GMT
Hi Kirran,

By "callback" do you mean something like a Spring init-method or a JSF @PostConstruct call?

There is no feature in Digester specifically for this, but I guess there are a couple of ways
to emulate it.

You mention the Digester.setStackAction method. Obviously the onPush method is no use, but
why not use onPop? (assuming you have some annotation or implemented interface that tells
you which objects to init, and which to ignore).

An object on the stack can be "initialised" via either xml attributes or nested child elements.
In the second case, there is no generic way to know when an object has been fully initialised
until all the nested rules have been executed. So onPop seems an entirely appropriate place
to inspect objects for initialisation annotations or interfaces.

Simply adding a CallMethodRule to invoke an init method as the first rule after the CreateObjectRule
that creates the object will have a very similar effect - CallMethodRules are invoked in reverse
order (see the wiki) so the first one registered will be invoked just before the object is
popped from the stack.

I guess it would be quite nice for SetPropertiesRule to take an init-method parameter, which
it invokes after the props are set. For objects that only need xml attributes, that works
nicely as the method can be called before child elements are processed.

Adding one to ObjectCreateRule, however, is only a very minor convenience. It would need to
be called on rule end, making it effectively no different than the manual adding of a CallMethodRule
rule.

Do you perhaps have a situation where you need objects initialised before they are passed
to their parent via a SetNextRule? Then you should see the wiki FAQ:
 http://wiki.apache.org/jakarta-commons/Digester/FAQ
entry:
  How do I get CallMethodRule to fire before SetNextRule?

Regards,

Simon

---- kirran <srik.bussa@gmail.com> schrieb:
> 
> Hi,
> these examples really helped me. But I could n't figure out how to get a
> callback on each object being populated. Surely i can get a callback by impl
> 'onPush'. But the object i get there is a newly created one. I 'd appreciate
> if you can let me know of a way to get each object being populated as
> against a new obj.
> thanks in advance.


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