On Mon, Apr 30, 2012 at 3:34 PM, David Winslow <[email protected]> wrote:
> Not to hijack the catalog discussion, but I will have some time later this
> week to work on implementing an output mode for the WMS GetCapabilities
> response to have it omit errant layers instead of generating invalid XML.
> If you have more detailed thoughts on "transactional" XML encoding I am
> interested to hear them. (The rough idea, buffer starting with an open tag
> until a closing tag is encoded, is pretty straightforward but I am not very
> familiar with the APIs and implementations involved.)
Let me see, I had in mind two ideas to make the usual TransformerBase
subclass handle "transactional" writes,
one based on command recording, the other based on output stream buffering.
The first one basically is based on the observation that the code going
through TransformerBase basically
writes XML via a handful of methods, start/end/chars/cdata, so one may put
the code in "recording mode"
and just record the calls to those methods but not make them act on the
ContentHandler,
see if we can encode stuff, and on "commit" replay those against
the actual contentHandler, otherwise throw away the list of recorded
commands on "rollback".
A lower level approach is based on the idea that regardless of what you do
you go through a OutputStream,
so one could create a wrapper that can switch between stream and in memory
buffer mode, put it
in buffer mode before starting to write a layer, write it, in case of
success write the buffer contents to the
actual stream, in case of failure just throw away and move on.
This seems simpler and may have a smaller footprint, at the same time we
have a few levels of abstraction
in between so we may not be 100% sure of what the layers above are doing,
which might result in
switching to buffer mode and receiving some content that we though we
should have already written
out after the switch (which would happen if anything above the output
stream does some of its own buffering).
Cheers
Andrea
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Ing. Andrea Aime
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