Web Technology Introduction

Collin Smith (Dec. 16, 2006)

AJAX AJAX

AJAX OutlineAJAX OutlineAJAX OutlineAJAX Outline

What is AJAX? Benefits Real world examples How it works Code review Samples

What is AJAX?What is AJAX?What is AJAX?What is AJAX?

Asynchronous JavaScript and XML(AJAX)

Web development technique for creating web applications Makes web pages more responsive by exchanging small

amounts of data Allows the web page to change its content without

refreshing the whole page A web browser technology independent of web server

software

BenefitsBenefitsBenefitsBenefits

Improves the user experience Analyzing information typed into browser in real time Provide a richer experience Increases responsiveness of web pages

Improve bandwidth utilization Only data which is required is retrieved from the server

Real World ExamplesReal World ExamplesReal World ExamplesReal World Examples

Google Maps (http://maps.google.com/) (slidable maps)

My Yahoo! (http://my.yahoo.com/) (shuffling windows)

How it worksHow it worksHow it worksHow it works

AJAX runs in your browser

Works with asynchronous data transfers(HTTP requests) between the browser and the web server

Http requests are sent by javascript calls without having to submit a form

XML is commonly used as the format for receiving server data but plain text may be used as well

1 – XMLHttpRequest object1 – XMLHttpRequest object1 – XMLHttpRequest object1 – XMLHttpRequest object

A page element must make a javascript call

The javascript function must create an XMLHttpRequest object which is used to contact the server

Javascript must determine whether the client is IE or Firefox

http = new ActiveXObject("Microsoft.XMLHTTP"); (IE)

http = new XMLHttpRequest(); (Mozilla)

2 - Sending the request2 - Sending the request2 - Sending the request2 - Sending the request

Once the XMLHttpRequest object has been created it must be set up to call the server

http.open("GET", serverurl, true); http.onreadystatechange = jsMethodToHandleResponse; http.send(null);

The code above utilizes the XMLHttpRequest object to contact the server and retrieve server data

When the response returns the javascript method jsMethodToHandleResponse can update the page

3 - Handling the Response3 - Handling the Response3 - Handling the Response3 - Handling the Response

Implementation of the javascript method which will be used to handle the response (Event Handler)

function jsMethodToHandleResponse(str) { //simply take the response returned an update an html

element with the returned value from the server document.getElementById("result").innerHTML = str; }

Now the page has communicated with the server without having to refresh the entire page

readyState propertyreadyState propertyreadyState propertyreadyState property

The XMLHttpRequest readyState property defines the current state of the XMLHttpRequest object

Possible values for the readyState

Usually we are usually only concerned with state 4

State Description

0 The request is not initialized

1 The request has been setup

2 The request has been submitted

3 The request is in process

4 The request is completed

Sample CodeSample CodeSample CodeSample Code

Simply unzip the sample code into a JSP Location and go to index.jsp

There are various examples that show some AJAX functionality

It is all JSP to make it easy to setup and easy to see the code.

The JSPs are generic enough to be easily to converted to other technologies (.NET or PHP)

ReferencesReferencesReferencesReferences

http://en.wikipedia.org/wiki/Ajax_%28programming%29 http://www.w3schools.com/ajax/default.asp