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AJAX. Ronen Cooper Roy Ben-Ami. 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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Ajax

AJAX

Ronen Cooper

Roy Ben-Ami

AJAX


Contents

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


What s ajax

What’s Ajax

  • Ajax may sound familiar…

    • Washing Machine powder

    • Dutch soccer team

AJAX


What s ajax1

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


What s ajax2

What’s Ajax

Google Suggest

Microsoft Live

Examples

From the Web

Writely

Google Maps

Gmail

AJAX


What s ajax3

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


Classic model

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


Classic model1

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


Ajax model

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


Ajax model1

Ajax Model

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

AJAX


Ajax model2

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.

AJAX


Defining ajax

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.

AJAX


Xhtml css

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


Ajax

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


Xml xslt

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 XSLTransformations

    • 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


Xmlhttprequest

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


Xmlhttprequest1

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


Javascript

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


Javascript1

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


Small example

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.

AJAX


Small example1

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>

AJAX


Ajax advantages

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


Ajax disadvantages

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


Ajax alternatives

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


Ajax alternatives1

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


Ajax alternatives2

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


Ajax alternatives3

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.

AJAX


Ajax alternatives4

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.

AJAX


Ajax alternatives5

Ajax Alternatives

AJAX


Enhanced ajax

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


Enhanced ajax1

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

AJAX


Enhanced ajax2

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);

}

public class Data {

public String[] getOptions() {

return new String[]{“1”,”2”,”3”};

}

}

function populateList(data) {

DWRUtil.addOptions(“listid”,data);

}

AJAX


Enhanced ajax3

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

AJAX


Ajax

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.

AJAX


Installation

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)

AJAX


Installation1

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

AJAX


Installation2

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).

AJAX


Installation3

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>

AJAX


Installation4

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.

AJAX


Raw xmlhttprequest

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

AJAX


Raw xmlhttprequest1

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

AJAX


Raw xmlhttprequest2

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.

AJAX


Raw xmlhttprequest3

Raw XMLHttpRequest

package myajax;

public class VoteSystem {

  • The Java Bean (VoteSystem.java)

private static int linux=0;

private static int windows=0;

private static int solaris=0;

private static int cares=0;

public String[] vote(int number) {

switch(number) {

case 1:

linux++;

break;

case 2:

windows++;

break;

case 3: …

}

return new String[]{linux+"",windows+"",solaris+"",cares+""};

public VoteSystem() {}

AJAX


Raw xmlhttprequest4

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>"

%>

AJAX


Raw xmlhttprequest5

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()

AJAX


Raw xmlhttprequest6

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>

AJAX


Raw xmlhttprequest7

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

AJAX


Direct web remoting

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.

AJAX


Direct web remoting1

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>

AJAX


Direct web remoting2

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>';

AJAX


Direct web remoting3

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>

AJAX


Bonus

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>

AJAX


Thank you

Thank You

The END!

AJAX


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