Thanks for this discussion/background Andrea.
While I can think of bad ways to fake an interceptor kind of workflow (give
each request a scratch area to work with, call all the interceptors and let
them collaborate in the scratch area) it seems like a lot of effort to
duplicate something we already have working with the dispatcher.
Other idea was to look for any examples of using spring mvc with OGC
services ... a long shot but I found:
https://github.com/gvSIGAssociation/gvsig-web-fw
--
Jody Garnett
On Mon, 23 Apr 2018 at 06:45, Andrea Aime <[email protected]>
wrote:
> 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:
>
> https://github.com/geoserver/geoserver/blob/master/src/community/wfs3/src/main/java/org/geoserver/wfs3/WFS3Filter.java
>
> https://github.com/geoserver/geoserver/blob/master/src/community/wfs3/src/main/java/org/geoserver/wfs3/DefaultWebFeatureService30.java
>
> 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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> ==
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> @geowolf
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>
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