Scripting languages | Technology Tales

Exploring AJAX

7^th June 2007

When I started it, my online photo gallery started out simply as a set of interlinked HTML pages. Over time, I discovered frames (yes, them!) and started to make use of JavaScript to make the slideshows slicker. In those days, I was working off free webspace provided by my ISP and client-side scripting was the only tool that I had for enhancing functionality. Having tired of the vagaries of client-side scripting while the browser wars were in full swing and incompatibilities reigned supreme, I went with paid hosting to get access to tools like Perl and PHP for server-side processing. Because their flexibility compared to JavaScript was a breath of fresh air to me, I am still a fan of the server-side approach.

The journey that I have just described is one that I now know was followed by many website builders around the same time. Nevertheless, I have still held on to JavaScript for some things, particularly for updating the DOM as part of making the pages more responsive to user interaction. In the last few years, a hybrid approach has been gaining currency: AJAX. This offers the ability to modify parts of a page without needing to reload the whole thing, generating a considerable amount of interest among web application developers.

The world of AJAX is evidently a complex one, though the underlying principle can be explained in simple terms. The essential idea is that you use JavaScript to call a server-side script, PHP is as good an example as any, that returns either text or XML that can be used to update part of a web page in situ without the need to reload it as per the traditional way of working. It has opened up so many possibilities from the interface design point of view that AJAX became a hot topic that still receives much attention today. One bugbear is efficiency because I have seen an AJAX application lock up a PC with a little help from IE6. There will always remain times when server-side processing is the best route, even if that needs to be balanced against the client-side approach.

Like its forbear DHTML, AJAX is really a development approach using a number of different technologies in combination. The DHTML elements such as (X)HTML, CSS, DOM and JavaScript are very much part of the AJAX world but server-side elements such as HTTP, PHP, MySQL and XML are also very much part of the fabric of the landscape. In fact, while AJAX can use plain text as the transfer format, XML is the one implied by the AJAX acronym and XSLT is used to transform XML into HTML. However, AJAX is not limited to the aforementioned technologies; for instance, I cannot see why Perl cannot play a role in place of PHP and ASP, both of which can be used for the same things.

Even in these standards-compliant days, browser support for AJAX remains diverse, to say the least, and it is akin to having MSIE in one corner and the rest in the other. Mind you, Microsoft did introduce the tools in the first place only for them to use ActiveX, while Mozilla created a new object type rather than continue this method of operation. Given that ActiveX is a Windows-only technology, I can see why Mozilla did what they did, and it is a sensible decision. In fact, IE7 appears to have picked up the Mozilla way of doing things.

Even with the apparent convergence, there will continue to be a need for the AJAX JavaScript libraries that are currently out there. Incidentally, Adobe has included one called Spry with Dreamweaver CS3. Nevertheless, I still like to find out how things work at the basic level and feel somewhat obstructed when I cannot do this. I remember perusing Wrox’s Professional AJAX and found the constant references to the associated function library rather grating; the writing style didn’t help either.

My taking a more granular approach has got me reading SAMS Teach Yourself AJAX in 10 Minutes as a means for getting my foot in the door. As with their Teach Yourself … in 24 Hours series, the title is a little misleading since there are 22 lessons of 10 minutes in duration (the 24 Hours moniker refers to there being 24 lessons, each of one hour in length). Anything composed of 10-minute lessons, even 22 of them, is never going to be comprehensive but, as a means for getting started, I have to say that the approach seems effective based on this volume. It has certainly whetted my appetite for giving AJAX a go, and it’ll be interesting to see how things progress from here.

SQL Developer Java error

6^th June 2007

Last night, I tried starting up Oracle's SQL Developer so that I could add a listing of my hillwalking blog posts to my website's site map with a spot of PHP scripting. However, all that I got was something like that which you see below:

Java Error returned on launching Oracle SQL Developer

I must confess that this one threw me. The solution, though challenging to find (they often are, even with the abilities of Google) was to use a batch file called sqldeveloper.bat that you can find in the [installation directory]\sqldeveloper\bin directory. It does start the thing when all else seems to fail and got me up and running again. I did get that blog post listing added to the site map after all; Having more visibility of the MySQL tables was a definite plus point.

Photo gallery trouble

4^th June 2007

The recent woes at Zooomr (mustn't forget that it is spelt with three O's...), have prompted me to ponder photo galleries. My own is a self-hosted affair, with Perl doing the honours of reading and processing data stored in an XML file. It may seem an unsophisticated system, but it has worked well and, apart from the matter of server administration, I am in full control. Yes, there is a development and maintenance overhead, but I enjoy programming and scripting anyway; I just have to find the time for it. If this is not your idea of fun, then using a service like Flickr, Zooomr or Photobucket is attractive so long as things don't go awry as they have for Zooomr and all the bad publicity and user frustration can't have done Zooomr's future prospects any good at all.

Using Korn shell commands in scripts running under the bash shell

19^th May 2007

This is actually a fairly simple one: just prefix the relevant command with ksh like below (in the example below, bash won't know what to do with the print command otherwise):

ksh print "Hello, world!"

It's also useful for running Korn shell scripts under the bash shell as well.

Recalling previous commands in the Korn shell

18^th May 2007

The default shell on Solaris boxes seems to be Korn and the version that I have encountered doesn't appear to allow obvious access to the command history. In the bash shell, the up and down cursor keys scroll through your command history for you, but Korn doesn't seem to allow this. Thankfully, there is another way: you can set up the editor vi as the default method for gaining access to the command history by adding the following line to the .profile file in your home directory:

set -o vi

Then, you can use the Vi (it's pronounced vee-eye, apparently) commands ESC+h and ESC+j to move up and down the list of previous commands. That, or, assuming that you have access to it, just use the bash shell anyway...

Checking existence of files and directories on UNIX using shell scripting

23^rd April 2007

Having had a UNIX shell script attempt to copy a non-existent file, I decided to take another look for ways to test the existence of a file. For directory existence checking, I was testing for the return code from the cd command, and I suppose that the ls command might help for files. However, I did find a better way:

if [ -f $filename ]
then
    echo "This filename [$filename] exists"
elif [ -d $dirname ]
then
    echo "This dirname [$dirname] exists"
else
    echo "Neither [$dirname] or [$filename] exist"
fi

The -d and -f flags within the evaluation expressions test for the existence of directories and files, respectively. One gotcha is that those spaces within the brackets are important too, but it is a very way of doing what I wanted.

HTML Tidy for Windows

22^nd March 2007

Drupal has modules (Import HTML and its helper Static HTML together make up one option) for importing static (X)HTML pages into its database, and it needs HTML Tidy to work. Since I am playing with the thing on Windows, I went out and snagged the version for that OS. Being either lazy or bloody-minded, I tried an XHTML page with PHP code embedded in it and, needless to say, the thing choked. I must try it with plain XHTML instead.

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