[Geotools-devel] Improving parsing GML files without a reference to the schema

[Andrea A. <and...@ge...>]

Hi,
I'm looking into improving our ability to parse GML files whose reference
to the schema is invalid or unreachable, in other words, not usable.

Right now the parser generates a feature collection by reflecting the schema
out of the first feature, which causes issues some cases, like
missing elements in the first feature (because they are null), which will
be then not part of the schema, and will be pruned from any subsequent
feature too.

My first idea would be to mimic what we have in the GeoJSON module and
allow the client to perform two parses, one that would determine the best
feature type by scrolling over the GML (see
FeatureJSON.readFeatureCollectionSchema),
and a second one that can take the target feature type as a hint (see
FeatureJSON.setFeatureType).

These could be added as new methods to the GML facade class:
SimpleFeatureType GML.decodeSchema(InputStream in)
SimpleFeatureCollection GML.decodeFeatureCollection(InputStream in)

Internally I'd pass a custom FeatureTypeCache that is not caching anything
in the first
case, allowing each feature to have its own natural feature type, and the
second one
to prime the cache with the target feature type.

However, I was thinking that the same could be done in a single call, since
we'd
be getting a in memory feature collection anyways, so we can really just
figure
out the best fitting feature type, and then decorate the collection with a
retyping one that will be returned. This would be best done using a
PullParser,
as we could control how the collection gets build (otherwise we end with a
DefaultFeatureCollection that would spam the logs complaining the feature
type
of the last feature added is not the same as the collection one).

This would however incur in a bit of extra cost... but probably negligible
comparedf
to the GML parsing itself... at the same time, the PullParser  is not as
tested as the non pull one.

So, we have two solutions, one safe but slower, based on two methods, using
the normal
parser, and doing two scans, one faster but a litter bit more untested,
using
the PullParser.

Which avenue would be the preferred one? Mind, I'd also need to backport
this little
new feature

Cheers
Andrea

-- 
==
GeoServer Professional Services from the experts! Visit
http://goo.gl/it488V for more information.
==

Ing. Andrea Aime
@geowolf
Technical Lead

GeoSolutions S.A.S.
Via Poggio alle Viti 1187
55054  Massarosa (LU)
Italy
phone: +39 0584 962313
fax: +39 0584 1660272
mob: +39  339 8844549

http://www.geo-solutions.it
http://twitter.com/geosolutions_it

*AVVERTENZE AI SENSI DEL D.Lgs. 196/2003*

Le informazioni contenute in questo messaggio di posta elettronica e/o
nel/i file/s allegato/i sono da considerarsi strettamente riservate. Il
loro utilizzo è consentito esclusivamente al destinatario del messaggio,
per le finalità indicate nel messaggio stesso. Qualora riceviate questo
messaggio senza esserne il destinatario, Vi preghiamo cortesemente di
darcene notizia via e-mail e di procedere alla distruzione del messaggio
stesso, cancellandolo dal Vostro sistema. Conservare il messaggio stesso,
divulgarlo anche in parte, distribuirlo ad altri soggetti, copiarlo, od
utilizzarlo per finalità diverse, costituisce comportamento contrario ai
principi dettati dal D.Lgs. 196/2003.



The information in this message and/or attachments, is intended solely for
the attention and use of the named addressee(s) and may be confidential or
proprietary in nature or covered by the provisions of privacy act
(Legislative Decree June, 30 2003, no.196 - Italy's New Data Protection
Code).Any use not in accord with its purpose, any disclosure, reproduction,
copying, distribution, or either dissemination, either whole or partial, is
strictly forbidden except previous formal approval of the named
addressee(s). If you are not the intended recipient, please contact
immediately the sender by telephone, fax or e-mail and delete the
information in this message that has been received in error. The sender
does not give any warranty or accept liability as the content, accuracy or
completeness of sent messages and accepts no responsibility  for changes
made after they were sent or for other risks which arise as a result of
e-mail transmission, viruses, etc.

-------------------------------------------------------