ImageLoader overhaul needed
---------------------------
Key: GEOT-1536
URL: http://jira.codehaus.org/browse/GEOT-1536
Project: GeoTools
Issue Type: Bug
Components: core render
Affects Versions: 2.5-M0, 2.4-RC0
Reporter: Andrea Aime
Assignee: Jesse Eichar
Fix For: 2.4-RC1, 2.5-M1
ImageLoader has a couple of issues I'm going to discuss now.
First of all, let's consider that the only code that still uses ImageLoader is
the SLDStyleFactory, which uses it to load external graphics in non interactive
mode. At the current state, there is no code trying to use that class in
interactive mode.
The responsibilities for ImageLoader are:
* load external images, eventually returning null immediatly but keep on
loading the file in the background (interactive mode)
* load external images blocking the caller (non interactive mode)
* cache the results so that the image loading does not occurr over and over
again
Image loading is done using MediaTracker, a bunch of sleep(xxx) and a 10
seconds timeout which is probably the cause
of the issues we're seeing in GeoServer (see linked issue).
If we give up interactive loading (which is not used), we could load an image
by simply using ImageIO.read(url), that would
be simpler and possibly more reliable.
Image caching is to be kept, but current code has two limitations:
* image cache is static and unbounded, meaning that once an image is loaded,
it'll stay there as long as the application lives. This may be troublesome,
especially if someone loads by mistake a big image instead of small icons.
Using a SoftValueHashMap should address this problem.
* the cache is keyed by url, no attempt is made to see if the file system or
the external server has a fresher copy of the data (maybe the content has been
replaced). We should avoid that and make sure the url does point to the same
data (e.g., if it's a file use latest modification date, if it's a http
connection consider caching limits or do a conditional get retrieving data only
if it has been modified after a certain date...
not sure there is any general way to do so, for http see
http://www.oreillynet.com/onjava/blog/2004/07/optimizing_http_downloads_in_j.html)
I would like your opinions on this one. Am I missing something? Any suggestions
on how to proceed?
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