Hi,
the KML2 module is almost ready as a KML module replacement, so I wanted to
give people an introduction to its features and design, given that the next
steps are going to be mostly bug fixes (unless I receive negative feedback
on some design elements of course).
As already reported in a previous thread (March 1st) the module builds KML
documents as object model trees based on the JAK library (
https://code.google.com/p/javaapiforkml/) and uses the JDK own JAXB library
to then serialize the resulting tree. Tests have been made to make sure
JAXB is not affecting WFS CITE tests.
There are three KML object model builders in the codebase, two of them
building a small KML made mostly of links, and one that is streaming, based
on lists that are evaluated as they are traversed:
https://github.com/geoserver/geoserver/tree/master/src/community/kml2/src/main/java/org/geoserver/kml/builder
For example, the simple network link builder just builds a kml with a
networklink for each layer:
https://github.com/geoserver/geoserver/blob/master/src/community/kml2/src/main/java/org/geoserver/kml/builder/SimpleNetworkLinkBuilder.java
The StreamingKMLBuilder instead builds a KML document containing a list of
folders (one per layer) that is generated as the list itself is traversed,
which in turn contains placemarks that are also generated as the list of
placemarks is traversed:
https://github.com/geoserver/geoserver/blob/master/src/community/kml2/src/main/java/org/geoserver/kml/builder/StreamingKMLBuilder.java
The streaming behavior is based on the Sequence construct, a simplified
iterator, and classes that wrap it to build enough List behavior to allow
JAXB to encode the output:
https://github.com/geoserver/geoserver/tree/master/src/community/kml2/src/main/java/org/geoserver/kml/sequence
If you look at the feature sequence factory and its sequence, you'll see
how the streaming encoding works:
https://github.com/geoserver/geoserver/blob/master/src/community/kml2/src/main/java/org/geoserver/kml/sequence/FeatureSequenceFactory.java
The interesting bit here is that a basic Placemark is built, and then its
contents are actually filled by pluggable decorators that do add the
geometry, title, description, style and so on:
https://github.com/geoserver/geoserver/tree/master/src/community/kml2/src/main/java/org/geoserver/kml/decorator
This makes it easy to add new content in placemarks, but will also allow to
completely separate GeoSearch as a clear cut plugin (still have to do this,
it's my next step after I've finished testing the KML generation and
compare all the outputs to the old KML generator).
The regionation code is still there, and has been isolated in its own
little package:
https://github.com/geoserver/geoserver/tree/master/src/community/kml2/src/main/java/org/geoserver/kml/regionate
All the crufty code to load the data and parse the styles have been
factored out in a bunch of small Visitor classes, plus a KMLFeatureAccessor
that binds them all togheter:
https://github.com/geoserver/geoserver/tree/master/src/community/kml2/src/main/java/org/geoserver/kml/utils
As you can see, generally speaking, each bit of the KML generation has been
split into smaller self contained classes having just one purpose. The old
KMLUtils is still there, but have a look and you'll see it really just has
a handful of utility methods left.
The code coverage is, at the moment, at 77%, but I plan to increase if
further as I progress with the interactive tests and find areas that are
not well covered.
Given that in 30 days we're going to have the feature freeze, I'm also
going to ask how we are playing with the upgrade.
I'm of course biased, but I feel this code is much more solid and more
understandable than the old code base, besides being easier to extend, so
if it was just for me I'd do a simple swap, kml2 in, old kml out.
My next step is to go through each page of the documentation about KML and
manually try each request and parameter described there, comparing it with
the outputs of the old module, to make sure there are no regressions (and
then create a geosearch2 that leverages the kml2 module).
Soo... what do you think?
Ah, if you want to build it as a replacement of the kml module, you can by
doing so:
mvn eclipse:eclipse -P\!kml,kml2
The \ is there to escape the ! which is otherwise interpreted as a signal
by the linux shell, if you are on another operating system you might not
need it (and oh, the ! is there to exclude the kml profile).
Well, let me know
Cheers
Andrea
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