Murray Collingwood wrote:
Hello again
I'm on the hunt for some sample code that will show me how to use my SQL Blob fields
to store images or documents.
Here's something on the Wiki to get you started:
http://wiki.apache.org/struts/StrutsFileDownload
The sample app posted there includes serving an image from a database.
For a while I entertained the idea of keeping the images and documents in a sub-
directory and simply referencing the file names but then I realised I was going to get
into trouble with synchronising the SQL data with the files on disk. For example, what if
somebody manually deleted one of the files, suddenly I need a bunch of conditions to
handle these inconsistencies.
Not sure what you mean here... it sounds like you need to store some
info in the database to give some details on what's on the file system,
but I'm not sure what you see as the problem here.
From my reading of Blobs in the SQL manual (MySQL 4.1) I can simply treat them like
objects and populate them into forms etc without any problem. So how do I get the
image to appear on the html page? Is it as simple as:
<html:img name="attributeName" property="myblob" /> ?
Not really... while I wouldn't be surprised if there was some provision
for getting a BLOB field to an Object, that's not what is typically done.
You need to understand the basic HTTP model here... let's say you do
some processing no the server and ultimately wind up in a JSP. The JSP
renders HTML, which is returned to the browser. Let's say the following
appears in the HTML:
<img src="myImage.gif">
Simple enough... what happens is the HTML is interpreted by the browser,
and a new request is made to the server for that image. It is at this
point you need to do something (maybe)... if the file is simply on the
file system, so long as the path is correct, the image will be returned.
What if the image is in the database though? You will need to have a
servlet (or Action) that retrieves the BLOB and returns it to the
browser. This is typically done by gettting a stream on the bytes of
the BLOB and writing them to the response.
How do I upload an image and capture it into a form?
Uploading is done using an <upload> element, presuming you are uploading
via HTTP. The important thing to note here is that Struts isn't really
involved... the BLOB will never be in the ActionForm for instance,
either when uploaded or downloaded. There are numerous examples of
accepting uploads in Struts, and any of these can be the basis for what
you are doing. You will just need to write the image to the database at
that point.
Regarding the SQL management of blobs, I'm assuming that it is better to create a
separate table for these with two columns, ID (int auto_increment) and IMAGE (blob),
and then to use the ID to reference the image on the other tables where it is linked.
Does this sound right to you?
Probably right... couldn't say for sure without knowing your DB schema a
bit.
--
Frank W. Zammetti
Founder and Chief Software Architect
Omnytex Technologies
http://www.omnytex.com
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