Technically, you can create a full Ajax application without ever using XML, but you will find XML to be a virtual necessity as your Web application grows in complexity. Here is how to do the same simple Web page with XML, once again cutting every corner for the sake of simplicity.
Notice in Listing 3 that we now grab the response with the code http.responseXML and extract the value we want with the code xmlDocument.getElementsByTagName('shipping'). Note also that the XML refers to the total with the tag shipping instead of totalshipping. This difference is unnecessary, but the purpose in this tutorial is to avoid the possible implication that the XML tag name and the HTML input field id must match in order to make the application work. They do not have to match.
Listing 3. index-xml.html
The only thing left is to modify our PHP code to return XML instead of plain text. See Listing 4 for the PHP code. In addition to the XML content itself, note the line of code that sends a header identifying the content as XML before returning the XML content itself. The XML places the shipping amount as a child of <order>, along with the unused data, <total>. This is simply a baby step toward representing a more realistic set of data that the page should return.
Listing 4. GetShippingXML.php
<?php $shipping="$5.00"; $total="$505.00"; $return_value = '<?xml version="1.0" standalone="yes"?> <order> <shipping>'.$shipping.'</shipping> <total>'.$total.'</total> </order>'; header('Content-Type: text/xml'); echo $return_value; ?>
Believe it or not, that's all there is to Ajax. Just about everything else that adds complexity to Ajax application development falls into the following categories.
A real Ajax application would not assume that the PHP file exists. It also would check the validity of the zip code before attempting to send it as a parameter to the server in order to find the shipping cost. (You also could have the server validate the zip code or do minimal validation at the client side, such as ensuring that the user entered five full digits and then perform full validation of the zip code at the server side.)
The above example eschews all error handling in order to keep the focus on the bare bones of how Ajax works. Obviously, you need to include input validation, error detection and error handling in a real application.
The above sample code works with Firefox, but there's no guarantee it will work in any other browser. If you want to write all your Ajax code from scratch, taking into account the variations between Firefox, IE and Opera, buy lots of ibuprofen—you'll need it. Fortunately, a plethora of Ajax libraries exist that manage the differences for you. One of my favorites is Dojo (see Resources).
Practical Task Scheduling Deployment
One of the best things about the UNIX environment (aside from being stable and efficient) is the vast array of software tools available to help you do your job. Traditionally, a UNIX tool does only one thing, but does that one thing very well. For example, grep is very easy to use and can search vast amounts of data quickly. The find tool can find a particular file or files based on all kinds of criteria. It's pretty easy to string these tools together to build even more powerful tools, such as a tool that finds all of the .log files in the /home directory and searches each one for a particular entry. This erector-set mentality allows UNIX system administrators to seem to always have the right tool for the job.
Cron traditionally has been considered another such a tool for job scheduling, but is it enough? This webinar considers that very question. The first part builds on a previous Geek Guide, Beyond Cron, and briefly describes how to know when it might be time to consider upgrading your job scheduling infrastructure. The second part presents an actual planning and implementation framework.
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- The Firebird Project's Firebird Relational Database
- Murat Yener and Onur Dundar's Expert Android Studio (Wrox)
- SUSE LLC's SUSE Manager
- Managing Linux Using Puppet
- My +1 Sword of Productivity
- Non-Linux FOSS: Caffeine!
- Google's SwiftShader Released
- Doing for User Space What We Did for Kernel Space
- SuperTuxKart 0.9.2 Released
With all the industry talk about the benefits of Linux on Power and all the performance advantages offered by its open architecture, you may be considering a move in that direction. If you are thinking about analytics, big data and cloud computing, you would be right to evaluate Power. The idea of using commodity x86 hardware and replacing it every three years is an outdated cost model. It doesn’t consider the total cost of ownership, and it doesn’t consider the advantage of real processing power, high-availability and multithreading like a demon.
This ebook takes a look at some of the practical applications of the Linux on Power platform and ways you might bring all the performance power of this open architecture to bear for your organization. There are no smoke and mirrors here—just hard, cold, empirical evidence provided by independent sources. I also consider some innovative ways Linux on Power will be used in the future.Get the Guide