|
 |
|
Comments
|
Today's Top SOA Links
AJAX An Introduction to AJAX and Taconite
Yes, it works
By: Tom Schreck; Jason Doyle
Jan. 25, 2007 01:45 PM
AJAX stands for Asynchronous JavaScript and XML. The core of AJAX is the use of the XMLHttpRequest() object to communicate with server-side scripts. It can send and receive information in XML, HTML, and plain text. The "Asynchronous" part means the client can communicate with the server without page refreshes. This allows you to update portions of a page based upon user events and is what allows developers to create Rich Internet Applications (RIA) using existing technologies.
The XMLHttpRequest object is not officially part of any Web standard, including W3C standards. Hence, the W3C created the Document Object Model Load and Save specification. Taconite is based on the concepts behind the W3C's Document Object Model Load and Save specification. The heart of Taconite is a parser that converts normal (X)HTML code into a series of JavaScript commands that dynamically create the content on the browser. This The Taconite custom parser is implemented as a set of JSP custom tags that can be used in any Java servlet container, or as a client-side JavaScript library, meaning it can be used in conjunction with virtually any server-side technology. Taconite focuses on removing the tedious task of writing large amounts of JavaScript to dynamically update content on a Web page. Unlike some frameworks that try to invent a new way of sending request data to the server, Taconite relies on the tried-and-true name/value pairs either embedded within the query string of a GET request, or tucked safely into the body of a POST. The client-side library even automates the creation of the name/value query string. All you need to worry about is telling Taconite what values should be sent to the server, and it takes care of the rest. Since the JavaScript is created by the parser based on the HTML you specify, you don't have to worry about dealing with browser JavaScript incompatibilities. The parser takes care of them all for you. All you need to do is specify the dynamic content as HTML, and the parser does the rest. InnerHTML Avoided The main problem with innerHTML is that it's non-standard. It is not specified by any W3C recommendation, although it is supported by most of today's browsers. Another problem with innerHTML is that it really only applies to HTML documents, not XHTML documents, which is what the industry is moving to. As browsers move to better, more strict support for XHTML documents, they may not support innerHTML due to its non-standard nature. Coming as a surprise to absolutely nobody, the innerHTML property has its own browser-to-browser quirks. For example, IE won't allow the innerHTML of a <table> to be appended. So, if you want to append one row to a table using innerHTML, you'll have to reproduce the entire contents of the table tag, with the one new row added at the end. That's just a waste of processing time and bandwidth. Using the innerHTML property doesn't lend much control when it comes to placing the new content. For instance, if you want to insert a table row between two existing table rows using the innerHTML property, you would have to reproduce the entire table. Taconite gives you the flexibility to specify where content should be placed. In fact, this concept is straight out of the W3C DOM Load and Save specification. Figure 1 shows the client HTML page. Note that there is only one link on the page (line 18). Clicking the link sends an AJAX request to the server, and the server's response is appended to the page. Lines 7 and 8 reference Taconite JavaScript files. The taconite-client.js file is always required when Taconite is used. This file defines the AjaxRequest object, which is the heart of the Taconite client-side library. The taconite-parser.js file references the JavaScript-based Taconite parser. It is only required when you wish to perform the XHMTL-to-DOM parsing on the browser rather than on the server. Lines 11-14 define the doHelloWorld function. Thanks to the Taconite framework, it's only two lines long. The first line creates an instance of the AjaxRequest object. The AjaxRequest object, as described by its name, encapsulates an AJAX request. Each instance of an AjaxRequest object creates its own instance of the XMLHttpRequest object, so you can create as many as you like without worrying about instances of XMLHttpRequest overwriting one another. Line 18 defines the link that initiates the AJAX request when clicked. The link calls the doHelloWorld function, passing to it the URL of the AJAX service to be called. The AjaxRequest object is created by passing a single argument to the object constructor. The argument is the URL to which the AJAX request will be sent. The second line of the doHelloWorld function sends the request to the server. The AjaxRequest object defines a sendRequest method, which is called here to send the request. The rest is defined on the server, which we'll look at next. Line 1 in Figure 2 is a directive indicating that the Content-Type of the page should be returned as text/xml. All Taconite responses must be returned with a Content-Type of text/xml, otherwise, the XMLHttpRequest object won't be able to parse it as an XML document. This file can be reproduced by any server-side technology; just set Content-Type to be text/xml. Line 3 has the taconite-root XML tag, which is the root tag of all Taconite responses. All Taconite responses must have the taconite-root tag as the root tag. The presence of this tag ensures that the response is well-formed XML. Note that the taconite-root tag has an attribute of xml:space="preserve." This is to ensure that Internet Explorer handles whitespace correctly. Line 5 opens the taconite-append-as-children tag. This tag says that the child elements of this tag will be appended as children to the context node. The context node is specified by the contextNodeID attribute. The value of this attribute must correspond to some element on the XHTML page. Remember the empty div element on Line 23 of the XHTML page, which had an ID attribute value of helloWorldContainer? This is where the message will be appended, because the contextNodeID attribute of the taconite-append-as-children tag has a value of helloWorldContainer. The second attribute on the taconite-append-as-children tag is parseInBrowser, which has a value of true (when not using the JSP tags, parseInBrowser must always be true). This tells the AjaxRequest object that it needs to parse the response into JavaScript before running the JavaScript to produce the "Hello World" message. Finally, the "Hello World!" message is defined on Lines 7-9. Notice how the message is simply defined as valid XHTML. In fact, the div tag even has an embedded style that makes the message font orange in color! This is the beauty of Taconite: you simply specify the new or updated content as regular ol' XHTML, and Taconite does the rest, without resorting to using the pesky innerHTML property. Using Taconite with ColdFusion
Reader Feedback: Page 1 of 1
Subscribe to the World's Most Powerful Newsletters
Subscribe to Our Rss Feeds & Get Your SYS-CON News Live!
|
SYS-CON Featured Whitepapers
Most Read This Week |
||||||||||||||||||||||||||||||||||||||||
|
|
| | | | | | | | |
|
|
|
|
|
|
| | | | | | | | | | | | | | | | | | | | | | | | | | |
|
|
| SYS-CON MEDIA: | | | | |
| SYS-CON EVENTS: | | | | | |
| INTERNATIONAL SITES: | | | | | | | | | | |
 |
Terms of Use & Our Privacy Statement  About Newsfeeds / Video Feeds |
| Copyright ©1994-2008 SYS-CON Publications, Inc. All Rights Reserved. All marks are trademarks of SYS-CON Media. |
| Reproduction in whole or in part in any form or medium without express written permission of SYS-CON Publications, Inc. is prohibited. |
.gif)
parser allows the developer to write content in a way that is natural - as (X)HTML. You no longer have to crowd your pages with a slew of document.createElement and document.appendChild commands to dynamically create new content. The resulting JavaScript is evaluated by the browser's JavaScript engine to produce the content specified by the (X)HTML. All you need to do is make sure that the content being generated is valid XHTML. That means single tags must be self-closing, attributes need to be in quotes, special characters need to be escaped and attribute minimization must be avoided (i.e., nowrap should be nowrap="nowrap").
