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From Upayavira ...@odoko.co.uk>
Subject Re: Extending the image reader
Date Mon, 30 Jan 2006 10:00:10 GMT
Tim Williams wrote:
> I want the image reader to accept a variant name (e.g. "thumb",
> "small") and then write the newly created image variant to disk before
> sending the output.  In other words, so that a given image
> "IMG001.jpg" might be "read" with a variant "thumb" and on disk would
> now be:
> IMG001.jpg
> IMG001.thumb.jpg
> 
> Obviously, a hefty cost for the first time through on each image but
> just reading afterwards.  I've initially done this by just copying the
> entire ImageReader into a new PersistentImageReader and inserting the
> applicable code in setup() and processStream().  Now that it's working
> how I'd like, I figured I'd just extend the ImageReader and only
> implement these two methods.  The only way I can think to do it is
> somehow redirect the output into a buffer, write the buffer, then send
> it out.  Is there a better way to extend a reader?  Anyone have any
> clues as to how I might be able to buffer the ImageReader's output?

Well, sounds like you're trying to achieve something similar to caching.
I wonder if the caching system might be an alternative approach to
achieving the same thing.

Anyway, to answer your question directly...

The AbstractReader class has a setOutputStream method. You could, in
your generate() method:
 * check to see if the resource has already been generated. If it has,
   set the inputSource to that of your cached version and proceed as
   normal (calling super.generate())
 * Otherwise, take a copy of the existing output stream, set the output
   stream (using setOutputStream) to your own buffering version. Proceed
   as normal. At the end of the generate method you write the contents
   of buffer to disc, then copy contents of buffer to original output
   stream.

I think that would work. And this should work as an extension of the
ImageReader class as you suggest.

Have I understood your question?

Regards, Upayavira

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