I worked on an app where we had cache set to false for Struts. In that
context, using an Action to retrieve the images prevented any of them from
being cached, which was bad for server load and site performance. We were
using Struts 1.0.2, though perhaps Struts 1.1 allows you to set the cache
behavior of each mapping/Action individually, which would have solved our
performance issue for the most part.
In light of that, we wrote a little servlet to serve the images. We also
implemented getLastModified() to retrieve the last modification time of the
requested image (which was also stored in the database). This worked great,
because the images would be cached by the browser until they were updated in
the db. I am not sure if that (last modification time) is supported in
Struts 1.1 either, but it would be another nice thing to have for
applications like this.
As a side note, storing the images in the db was been very nice for us
generally. Having all the data in the database is very convenient for
deployment, since there are no filesystems to worry about and no chance that
the filesystem would be out of sync with the db (where you would likely
still store references to the binary data, stored as files in such a
scenario). The performance was fine with the caching sorted out. We didn't
do any rigorous comparisons to disk-based storage, but rather the
performance just turned out to not be an issue for this project after the
caching was fixed.
Perhaps this already exists, but it would be very cool to have a system that
stored (or simply allowed storage of) the image (or any similar binary data)
in the db and then cached them to a local disk for performance. This would
be a great J2EE or Struts-specific open source project for someone to make
available. You'd get the convenience of db storage and the performance of
disk storage. You could even provide a custom tag library to construct a tag
(or URL) from the image/resource ID, set the size of image in the HTML, or
perhaps adjust the src URL for direct access to the disk file for cached
images. Though watch out for stale caches in that last scenario -- perhaps
the mod times of the disk file versus the db blob could be checked when the
tag is processed to avoid that problem. The image could even be
pre-emptively written to the cache (assuming it is stale or not yet cached)
when the tag is processed to always be able to write a URL to the file in
the cache rather than to a servlet for processing. You might run into
trouble if someone references the image from another site or something
though, so that might not be that great after all. That is unless you have a
404 handler that could look it up in the cache if it is found to be missing
on disk and reset the response code back to 200 and serve the image data
from the db, which might be worth a try. The 404 handler idea would allow
operation with a fixed maximum disk cache size, or avoid problems if you
simply ran out of disk space to cache to, also. Or perhaps it would be
simpler and just as fast to pass all requests for images through a servlet,
since you'd be doing much the same kind of stuff that the FileServlet would
be doing to serve the image anyway. Non-image specific tags would also be
useful for other kinds of binary data stored in the db. This could be a
great project if there isn't one out there already.
-Max
- Original Message -
From: Nicolas De Loof [EMAIL PROTECTED]
To: Struts Users Mailing List [EMAIL PROTECTED]
Sent: Wednesday, April 02, 2003 12:46 AM
Subject: Re: How to use Struts to show image from database (byte[])?
You can migrate your original ImageServlet as Struts action :
Put servlet code inside execute() method of a new ImageAction class, that
sends image byte[] and content-type headers in
response, then returns null.
Add an action-mapping for ImageAction (let's say /image.do) and you will
be able to use /myApp/image.do?imageID=x
Nico.
Subject: How to use Struts to show image from database (byte[])?
I have images in database.
Prior to Struts I use servlet to show image and in JSP or sevlet. I have
/myPackage/imageservlet?imageID=1
How to use Struts to show image from database (byte[])?
Thanks.
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