Hi,
as you know we have a WFS 3.0 prototype implementation in community land. Right now it’s implemented
mostly as an internal proxy to WFS 2.0:
The other possible alternative for implementation would have been to use Spring MVC… however that would have come
with a very high cost, as it would have broken solid all usage of DispatcherCallback, making WFS3 problematic to use
in the GeoServer ecosystem.
Here is a small recap of supported functionalities that would be broken by a WFS implemnetation not going go through the Dispatcher and does
not invoke DispatcherCallback:
- Version negotiation
- Workspace specific services
- Monitor extension
- Service security
And then add to that whatever extra callback is present in vendor implementations of GeoServer (in my experience it’s one
of the most used callbacks).
Now, not going throught the Dispatcher does not equate with not calling DispatcherCallback, but it’s pretty close.
The main issue is that not all callbacks are read only, and each method allows implementors to alter the call in many ways:
-
init allows to fiddle with kvp maps, allowing to alter them, or redefine them from scratch
-
serviceDispatcher allows to re-route to another service (we do that, for example, in the ncwms module, and I believe in the WFS NSG modules too)
-
operationDispatched allows to change the parsed request parameters, or to re-route to an entirely different call (done multiple times in vendor extensions, e.g., to bypass GeoServer completely and call other services in the infrastructure that could compute some GetMap responses with higher efficiency)
-
operationExecuted allows to rewrite the response object (e…g, to enrich/decorate/filter the response)
-
responseDispatched allows to change the response object that will encode the response (allows for alternate encoding implementation)
-
finished… is just finished, no changes allowed here
In Spring MVC I see none of this flexibility, yes one can add interceptors, but they are working at low level HTTP and would end up being shared with the configuration API, and believe one can build proxies around controllers, but their support of the above would seem rather limited compared to the above (change http kvp, change single method request and response objects). So even adding a proxy around the controller, the support for callback would be severely limited and would not fit the existing architecture, breaking them in case WFS 3 is used.
The above makes me believe MVC is not actually viable to implement OGC resource oriented services, as a result, I’ll probably continue
to work on the current proxy based approach, and see how deep the rabbit hole is.
But… I’d like to hear from others, that surely have more MVC famliarity than me, and see if there is any viable alternative
Cheers
Andrea
···
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Ing. Andrea Aime
@geowolf
Technical Lead
GeoSolutions S.A.S.
Via di Montramito 3/A
55054 Massarosa (LU)
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