Kohsuke Kawaguchi wrote:
> Dan Diephouse wrote:
>> Hi,
>> I am working with the JAXB attachment support and have run into a bit
>> of a quandary. When I'm marshalling my JAXB objects, its easy enough
>> to pass in my AttachmentMarshaller and receive notification that I
>> have attachments. However, that doesn't do me much good as at that
>> point I am already in the midst of sending my response. Is there
>> anyone way to figure out if there are attachments that need to be
>> written before I marshal?
>
> Right. It's a bit of catch-22 situation.
>
> Scanning the whole tree once just to see if there's any binary is
> expensive, and we can't do this very nicely today (in short of
> marshalling to /dev/null.) But that's an option --- namely, marshal it
> once to a dummy OutputStream just to see if you have binary attachment.
>
> Another approach that can be done today is to buffer the marshalling
> result until you know if there's an attachment or not. If you do find
> an attachment you can stop buffering at that point and do things full
> speed. But if your XML is big and attachments aren't often, then this
> would slow things down.
>
> The third approach is to always enable the attachment support upfront
> (IOW write a MIME envelope for XOP) --- I think this is what JAX-WS RI
> is doing.
>
> The fourth approach that requires some changes in the RI is, when we
> build a JAXBContext, maybe we can check if a given class may
> potentially contain a binary data in its descendants, and give you
> that information.
>
> Assuming that you are using it for XFire, that would let you say "this
> operation has parameters Foo, Bar, and String, and none of them can
> contain binary data at all, so let's turn off the attachment". If a
> tree can statically contain binary data but it actually didn't then
> you lose, but hopefully that's not big enough lose.
>
>
> Can you think of any other ways to do this better? Do you want the 4th
> approach?
>
OK, that was what about what I thought. I really can't think of anyway
to do it better. Now in XFire it works one of two ways - 1. set the
mtom-enabled flag, and then we always write it in MIME format. Or 2. if
we're in DOM mode (i.e. for WS-Security), it already caches the output
so we can figure out if there are attachments before we write.
I don't think there is any great way to do it. After thinking about it
more, I think ultimately MTOM does just need to be a flag, since its an
optimized transmission. I.e. the WSDL isn't saying this byte[] data has
to be an attachment. Although maybe a ws-policy provides a way to do that?
Another random question - is there any way to have JAXB generate a
DataHandler/DataSource instead of a byte[] array?
Thanks!
- Dan
--
Dan Diephouse
Envoi Solutions
http://envoisolutions.com
http://netzooid.com/blog