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AJAX

Ronen Cooper

Roy Ben-Ami

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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

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What’s Ajax

Ajax may sound familiar… Washing Machine powder Dutch soccer team

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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!

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What’s Ajax

Google Suggest Microsoft Live

Writely Google Maps

Examples From the

Web

Gmail

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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

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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

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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

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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

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Ajax Model

Every user action that normally would generate an HTTP request takes the form of a JavaScript call to the Ajax engine

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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.

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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

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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

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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.

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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!

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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.

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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)

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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.

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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.

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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?

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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.

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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.

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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.

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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”}; }}

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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!