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AJAX 1
AJAX
Ronen Cooper
Roy Ben-Ami
AJAX 2
Contents
What’s Ajax? Classic Model Vs. Ajax Model Defining Ajax
XHTML, DOM, XML, XMLHttpRequest, JavaScript Advantages & Disadvantages Ajax Alternatives
XUL, XAML, Applets, Flash, SVG Enhanced Ajax
DWR, Xajax, Ajax.Net Examples + Demo
AJAX 3
What’s Ajax
Ajax may sound familiar… Washing Machine powder Dutch soccer team
AJAX 4
What’s Ajax
Ajax is the buzzword of the moment among web developers
It Stands for Asynchronous JavaScript And XML Jesse James Garrett invented this bad acronym
in Feb 2005 to describe its use by Google. Most of the Ajax world is focused on the client
side, and "ooooh ahhhh" effects Lets see some of these effects!
AJAX 5
What’s Ajax
Google Suggest Microsoft Live
Writely Google Maps
Examples From the
Web
Gmail
AJAX 6
What’s Ajax
Ajax isn’t a technology Ajax is an approach to Web application
development that uses client-side scripting to exchange data with the Web server
Ajax is also more of a pattern -- a way to identify and describe a useful design technique
Ajax is new in the sense that many developers are just beginning to be aware of it, but all of the components that implement an Ajax application have existed for several years
AJAX 7
Classic Model
The classic web application model works like this: Most user actions in the
interface trigger an HTTP request back to a web server.
The server does some processing — retrieves data, crunches numbers, talks to various legacy systems
And then returns an HTML page to the client
AJAX 8
Classic Model
This approach makes a lot of technical sense, but it doesn’t make for a great user experience. At every step in a task, the user waits. The user sees the application go to the server
AJAX 9
Ajax Model
An Ajax application eliminates the start-stop-start-stop nature of interaction on the Web It introduces an intermediary, an Ajax
engine, between the user and the server.
Instead of loading a webpage, at the start of the session, the browser loads an Ajax engine, written in JavaScript and usually tucked away in a hidden frame.
The Ajax engine allows the user’s interaction with the application to happen asynchronously, independent of communication with the server
AJAX 10
Ajax Model
Every user action that normally would generate an HTTP request takes the form of a JavaScript call to the Ajax engine
AJAX 11
Ajax Model
Any response to a user action that doesn’t require a trip back to the server — such as simple data validation, editing data in memory, and even some navigation — the engine handles on its own.
If the engine needs something from the server in order to respond — if it’s submitting data for processing, loading additional interface code, or retrieving new data — the engine makes those requests asynchronously, usually using XML, without stalling a user’s interaction with the application.
The user is never staring at a blank browser window and an hourglass icon, waiting around for the server to do something.
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Defining Ajax
Ajax incorporates several technologies, each flourishing in its own right, coming together in powerful new ways.
standards-based presentation using XHTML, CSS dynamic display and interaction using DOM data interchange and manipulation using XML, XSLT asynchronous data retrieval using XMLHttpRequest and JavaScript binding everything together.
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XHTML, CSS
XHTML stands for EXtensible HyperText Markup Language It consists of all the elements in HTML 4.01
combined with the syntax of XML. CSS stands for Cascading Style Sheets
It is used to describe the presentation of a document written in HTML or XML.
AJAX 14
DOM
The HTML DOM is the Document Object Model for HTML . DOM provides a standard set of objects for
representing HTML and XML documents, and a standard interface for accessing and manipulating them.
Essentially, it connects web pages to scripts or programming languages.
It defines an HTML document as a collection of objects that have properties and methods and that can respond to events
AJAX 15
XML, XSLT
XML stands for EXtensible Markup Language XML was designed to describe data and to focus on
what data is (unlike HTML which was designed to display data and to focus on how data looks)
It is a general-purpose markup language for creating special-purpose markup languages that carry data.
XSL stands for EXtensible Stylesheet Language XSLT stands for XSL Transformations XSLT is used to transform an XML document into another
XML document, or another type of document that is recognized by a browser, like HTML and XHTML
AJAX 16
XMLHttpRequest
The kernel of Ajax is the XmlHttpRequest The XMLHttpRequest object allows client-side
JavaScript to make HTTP requests (both GET and POST) to the server without reloading pages in the browser and without blocking the user
This JavaScript object was originally introduced in Internet Explorer 5 by Microsoft (Gasp!, yes they actually invented something), and it is the enabling technology that allows asynchronous requests
Despite its name, you can use the XMLHttpRequest object with more than just XML. You can use it to request or send any kind of data.
AJAX 17
XMLHttpRequest
By performing screen updates on the client, you have a great amount of flexibility when it comes to creating your Web site : Eliminate page refreshes every time there is user
input Edit data directly in place, without requiring the user
to navigate to a new page to edit the data Increase site performance by reducing the amount of
data downloaded from the server The possibilities are endless!
AJAX 18
JavaScript
JavaScript is one of the world's most popular programming languages Its popularity is due entirely to its role as the scripting
language of the WWW along with VBScript
JavaScript has a syntax similar to Java but: It is not a real programming language (it is script) It was developed at Netscape and not Sun. It was originally called LiveScript, but that name
wasn't confusing enough.
AJAX 19
JavaScript
JavaScript binds all the mentioned technologies together to create the Ajax “pattern”. When a user clicks a button, you can use JavaScript and
XHTML to immediately update the UI Then you spawn an asynchronous request to the server
using the XMLHttpRequest object via JavaScript to perform an update or query a database.
When the request returns as XML, you can then use JavaScript, CSS, XSLT and DOM to update your UI accordingly without refreshing the entire page.
Most importantly, users don't even know your code is communicating with the server: the Web site feels like it's instantly responding ("desktop-like" usability)
AJAX 20
Small Example
In this example we have an HTML page: In it we have a link When we press it, it goes to another html page. Reads its content from the server. And pops an alert box with the content as a string.
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Small Example
if (window.XMLHttpRequest) http_request = new XMLHttpRequest();else if (window.ActiveXObject) http_request = new ActiveXObject(“Microsoft.XMLHTTP”);
http_request.onreadystatechange= alertContents;http_request.open(‘GET’, url, true);http_request.send(null);
if (http_request.readyState == 4) if (http_request.status == 200) alert(http_request.responseText);
<a href=“#” onclick=“makeRequest(‘test.html’)”> Make a request </a>
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Ajax Advantages
Client Side Can produce smooth, uninterrupted user workflow. Saves bandwidth by only transmitting new information Creates possibility of entirely new types of user interfaces
not possible in traditional model. Developer Side
Provides a Middle-of-the-Road approach between sophisticated web design (Java applets and Flash) to simple web design (HTML).
Doesn't require 3rd party software like Java or Flash Fits into normal code flow Most developers already know JavaScript.
AJAX 23
Ajax Disadvantages
Client Side Poor compatibility with very old or obscure browsers, and
many mobile devices. Limited Capabilities like multimedia, interaction with web-
cams and printers, local data storage and real time graphics.
The first-time long wait for Ajax sites. Problem with back/forward buttons and bookmarks.
Developer Side Easily Abused by “bad” programmers. Not everyone have JavaScript enabled. Too much code makes the browser slow.
AJAX 24
Ajax Alternatives
As a new technology moves through the hype curve, people emerge to raise the inevitable question "Why not something else?“
Now we have AJAX –
an admittedly powerful
approach to web development is that because it's really
the best option for the job?
AJAX 25
Ajax Alternatives
XUL Pronounced "zool", XUL is a high performance markup
language for creating rich dynamic user interfaces It’s part of the Mozilla browser and related applications
and is available in Mozilla browsers (like Firefox). XUL is comprised mainly of a set of high-performance
widgets that can be combined together Advantages: high performance, fast, works with
JavaScript, based on XML Disadvantages: Only compatible with Mozilla browsers.
AJAX 26
Ajax Alternatives
XAML
XAML is a high performance markup language for creating rich dynamic user interfaces.
It’s part of Avalon, Microsoft’s next generation UI technology (will be supported in IE 7).
Advantages: high performance, robust, highly configurable.
Disadvantages: Microsoft-only technology and will be available only when Vista is released.
AJAX 27
Ajax Alternatives Java Applets
An Applet is a program written in JAVA that can be included on a web page.
Advantages: Fast. Supported on most platforms (with the Java plugin).
Disadvantages: Requires the Sun Java plugin and takes a while to load.
Macromedia Flash & Shockwave (or the new FLEX) These are powerful presentation-layer frameworks. Advantages: Browser and platform compatibility. Speed
and flexibility. Increasingly powerful development tools. Disadvantages: General distrust from enterprise software
developers. Rare skillset required.
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Ajax Alternatives
SVG (Scalable Vector Graphics)
A text based graphics language that describes images with vector shapes, text, and embedded raster graphics.
It has good interoperability with CSS and JavaScript Advantages: Speed and flexibility. Disadvantages: Requires proprietary plugins that many
firms will not allow users to install. Rare skillset required to do development. This language is still somewhat immature and developing.
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Ajax Alternatives
XUL XAML SVG Flash Applets Ajax
Desktop-like UI
Platform Independence
Vendor Independence
Skill Set Transferrance
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Enhanced Ajax
Raw Ajax - using the XmlHttpRequest directly for creating asynchronous requests is cumbersome.
It is verbose in the JavaScript code and hard to debug. You must consider the server-side work needed to
marshal the results back to the browser Using different engines/frameworks you can
eliminate all of the machinery of the Ajax request-response cycle from your application code.
This means your client-side code never has to deal with an XMLHttpRequest object directly.
You don't need to write object serialization code or use third-party tools to turn your objects into XML.
AJAX 31
Enhanced Ajax
DWR – Direct Web Remoting It is a Java framework that you can easily plug into your
Web applications to allow your JavaScript code to call services on the server.
DWR is deployed as a servlet within your Web application DWR dynamically generates JavaScript to include in your
Web page for each exposed class The generated JavaScript contains stub functions that
represent the corresponding methods on the Java class and also performs XMLHttpRequests behind the scenes.
The DWR invokes those methods and sends the method's return value back to the client side in its servlet response, encoded into JavaScript
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Enhanced Ajax
This method of remoting functions from Java to JavaScript gives DWR users a feel much like conventional RPC mechanisms like RMI or SOAP, with the benefit that it runs over the web without requiring web-browser plug-ins.
function eventHandler() { Data.getOptions(populateList);}
function populateList(data) { DWRUtil.addOptions(“listid”,data);}
public class Data { public String[] getOptions() { return new String[]{“1”,”2”,”3”}; }}
AJAX 33
Enhanced Ajax
There are many more such frameworks for Java and other languages: Xajax - an open source PHP class library for ajax Ajax.net – Ajax library for .Net (not by microsoft) AjaxAnywhere - designed to turn any set of existing
JSP or JSF components into AJAX-aware components
Dojo - an Open Source toolkit that allows you to easily build dynamic capabilities into web pages
Bindows - object-oriented platform and IDE for developing Ajax applications
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Demo
The demo contains 2 identical examples for using Ajax. First example will use the raw XMLHttpRequest. Second example will use the DWR.
The examples show a way for creating the “next generation” voting system. Old system is used in sites like walla, ynet and more… Currently, when you vote the entire page is
refreshed/resent. Ajax can make the user experience more pleasant by
providing a more responsive UI and eliminating the flicker of the page refresh.
It also saves bandwidth since we can send only the results back, instead of the whole page.
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Installation
All we need to run Ajax is a compatible browser! Explorer, Mozilla or FireFox will do fine.
But to develop and test our examples we also need a Web Server. We will use Tomcat 5.5 which can be found here We will need Java SDK 1.5 (5.0) – get here
In general, you will also need a DB, but for simplicity we don’t use one in our examples.
Lastly, for the DWR example, you need to d/l the dwr.jar from here (version 1.0 or 1.1 beta)
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Installation
Install Tomcat by running the binary file (after JDK 1.5) Start the tomcat web server by clicking the “Configure
Tomcat” program. Press the Start. Wait until the service
status says Started. Open your browser. Enter the address:
localhost:8080
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Installation
Make sure you have this page now in the browser
Now place the dwr.jar in the WEB-INF/lib directory of your web app (default is TOMCAT_HOME/webapps/ROOT/ WEB-INF/lib).
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Installation
Now add these lines to the WEB-INF/web.xml file. The <servlet> section needs to go with the other <servlet>
sections, and likewise with the <servlet-mapping> section. <servlet> <servlet-name>dwr-invoker</servlet-name> <display-name>DWR Servlet</display-name> <servlet-class>uk.ltd.getahead.dwr.DWRServlet</servlet-class> <init-param> <param-name>debug</param-name> <param-value>true</param-value> </init-param> </servlet> <servlet-mapping> <servlet-name>dwr-invoker</servlet-name> <url-pattern>/dwr/*</url-pattern> </servlet-mapping>
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Installation
That’s it!!! It’s that simple. Notice that Tomcat also supports JSP files and
servlets (the Java equivalent to ASP.NET). All we need now is a Text Editor such as
notepad or something else free to write the code down.
Later we will go back to configure the DWR correctly for our example.
But for right now, lets jump to the 1st example.
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Raw XMLHttpRequest
To make our example, we need to program 3 files A Java Class (Bean) that will do the voting calculations. A JSP page on the server to transfer the client’s data to
the Java Class (Bean) and back. A DHTML+JavaScript page that the client will see & use
We will create 4 files: VoteSystem.java – The Java Bean voteRaw.html - The DHTML file voteRaw.js – The JavaScript file we will put in the HTML calcVotes.jsp – The JSP server file
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Raw XMLHttpRequest
All the “Web” files go into your main web app directory in tomcat (i.e webapps/ROOT)
The Java Bean file goes into the relevant package in webapps/ROOT/WEB-INF/classes (in our case the package is myajax)
In the demo, we will give you a zip file which you open in the webapps directory.
It will contain all the files in their correct places
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Raw XMLHttpRequest
Basically the client will see a voting box in his page He will click his choice Using JavaScript and the XMLHttpRequest it will make a
request to the server (the JSP file) The JSP file will then call the Java Bean, and give him the
client’s data. The bean will return the answers to the JSP who will
transform them to XML and send them to the client. The client will receive the answers asynchronously and
display them.
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Raw XMLHttpRequest
The Java Bean (VoteSystem.java)package myajax;
public class VoteSystem {
private static int linux=0;private static int windows=0;
private static int solaris=0;private static int cares=0;
public VoteSystem{} ()
public String[] vote(int number) {switch(number) {
case 1:linux++;break;case 2:windows++;break;case 3: …
}…return new String[]{linux+"",windows+"",solaris+"",cares+""};…
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Raw XMLHttpRequest
The JSP File (calcVotes.jsp)<%@ page import="myajax.*" %>
<%String rank=(String)request.getParameter("rank");VoteSystem voteSystem=new VoteSystem();int rankNum=Integer.parseInt(rank);String reply[]=voteSystem.vote(rankNum);response.setContentType("text/xml");
%><%="<vote>"+ "<linux>"+reply[0]+"</linux>"+ "<windows>"+reply[1]+"</windows>"+ "<solaris>"+reply[2]+"</solaris>"+ "<cares>"+reply[3]+"</cares>"+ "</vote>"%>
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Raw XMLHttpRequest
The JavaScript File (voteRaw.js)function castVote(rank)
req = window.XMLHttpRequest ? new XMLHttpRequest() : new ActiveXObject("Microsoft.XMLHTTP");req.onreadystatechange = handleResponse;req.open("GET","http://127.0.0.1:8080/calcVotes.jsp?rank="+rank, true);req.send(null);if (req.readyState == 4) { if (req.status == 200) { response = req.responseXML.documentElement; table=document.getElementById("votes"); linux='Linux:<b> '+response.getElementsByTagName('linux')[0].firstChild.data……table.rows[1].cells[0].innerHTML=linux;table.rows[2].cells[0].innerHTML=windows;…
function handleResponse()
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Raw XMLHttpRequest
The HTML File – Pretty long boring HTML Stuff… Only 2 related things: At the <head> section we put a link to the file we created:
At the Vote form we link the links to the functions in the JavaScript file:
<script type="text/javascript" src="voteRaw.js"></script>
<tr><td class="sidemenuitem" width="134" align="center"><a href="#" onclick="castVote(1); return false;">Penguin Guy</a></td></tr>
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Raw XMLHttpRequest
As you can see, this is a lengthy process but it works!
In order to improve that, we can use the DWR. Now we don’t need the JSP page anymore, and we
can call directly the Java Bean ourselves from the HTML page.
The DWR will take care of transferring all the data between the client and the java class (we don’t need to do anything).
Let’s see example 2
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Direct Web Remoting
DWR makes our lives much simpler but it’s a bit slower that regular AJAX, and also still buggy (getting better all the time).
To use DWR we need to do the following: We need to tell the DWR engine what classes and
methods we want it to “export” for us. We need to create a dwr.xml file and put it inside our
TOMCAT_HOME/webapps/ROOT/ WEB-INF In the dwr.xml we will specify our Java Class, and will give
it a JavaScript name that we can use in the HTML pages.
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Direct Web Remoting
The dwr.xml file we will use
We will now need to change a few things…
<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE dwr PUBLIC "-//GetAhead Limited//DTD Direct Web Remoting 1.0//EN" "http://www.getahead.ltd.uk/dwr/dwr10.dtd">
<dwr> <allow> <create creator="new" javascript="JSVoteSystem"> <param name="class" value="myajax.VoteSystem" /> </create> </allow></dwr>
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Direct Web Remoting
The new JavaScript File (voteDWR.js)
Notice how much simpler the functions are! And we don’t even need the JSP file!
All that is left is to add 3 lines to the HTML file.
function castVote(rank) {JSVoteSystem.vote(rank,handleResponse);
}
function handleResponse(data) {…$("votes").rows[1].cells[0].innerHTML='Linux:<b> '+data[0]+'</b>';$("votes").rows[2].cells[0].innerHTML='Windows:<b> '+data[1]+'</b>';…
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Direct Web Remoting
We add 3 lines to the HTML file
The util.js that DWR provides contains a lot of useful methods to use the DOM such as setValue(), getValue() and more…
The built-in Debug mode in DWR allows us to test our classes in here: http://localhost:8080/dwr/
For every function we exported, we will be able to test and see how it works remotely – really cool feature!
<script type='text/javascript' src='/dwr/interface/JSVoteSystem.js'></script><script type='text/javascript' src='/dwr/engine.js'></script><script type='text/javascript' src='/dwr/util.js'></script>
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Bonus
We added 2 more JavaScript files to demo genlibsubset_draggable.js & draggable.js These enable you to drag around stuff in your HTML
file – a cool thing to do. All you need to do is to include those 2 scripts in your
file and add the attribute class=“draggable” to anything that you want to drag.
You need to give a fixed size to those objects in order for it to work.
<script type="text/javascript" src="genlibsubset_draggable.js"></script><script type="text/javascript" src="draggable.js"></script>…<div class="draggable" style="position:absolute; left:10px; top:300px;" >…</div>
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Thank You
The END!