Transcript Catch Me If You Can

Making Progress
With Ajax
Peter van Dam
Agenda
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Agenda Item 1
Introduction
The XMLHttpRequest object
Calling Progress:
• WebSpeed
• Web services
 Ajax Frameworks
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What is Ajax?
Asynchronous JavaScript and XML
 Standards-based presentation using XHTML
and CSS;
 Dynamic display and interaction using the
Document Object Model;
 Data interchange and manipulation using
XML;
 (A)synchronous data retrieval using
XMLHttpRequest;
 and JavaScript binding everything together.
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What is Ajax? (2)
The bottom line
 A way to create web applications that behave
like desktop applications (Rich Internet
Application – RIA)
 Zero footprint
 Single Page Interface
 Almost as rich as the desktop
 But not a replacement for the desktop
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HTML, XHTML, DHTML
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HTML development ceased in 1999 (4.01)
Followed by XHTML (W3C standard)
No more browser-specific dialects
XHTML is like HTML 4.0 but enforces tag
rules stricter (e.g. close tags required:
<P></P> and <BR />)
 DHTML allows the dynamic manipulation of
web pages at runtime (see DOM)
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DOM
 The Document Object Model is a standard
API for accessing all objects in a web page
(document)
 An example language that implements the
DOM is JavaScript
 The DOM allows to query, create, modify and
delete elements in a web page at run time
 Examples: rendering, refreshing content (!)
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JavaScript
 JavaScript is a client-side programming
language that runs in the browser
 Standardized by ECMA
 Minor differences (additions) still exist, but it
is not a nightmare anymore
 As long as you stick to ECMAScript for
manipulating the DOM you are OK
 JavaScript is not difficult to learn
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CSS
 Cascading Style Sheets allow the separation
of presentation and data by defining Styles
 Look-and-feel is provided by CSS
 CSS offers more details than HTML
 Styles can be set by JavaScript as well, e.g.
field width in pixels
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CSS (2)
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XML
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The XMLHttpRequest object
The magic of Ajax is in the XMLHttpRequest object
The following code works in all modern browsers*:
function callServer(dataFile, target) {
var myRequest = new XMLHttpRequest();
var myTarget = document.getElementById(target);
myRequest.open("GET", dataFile, false);
myRequest.send(null);
myTarget.innerHTML = myRequest.responseText;
}
* IE 6- requires additional code
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The XMLHttpRequest object
Methods
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Method
Description
open(method, URL, async)
Specifies the method, URL and
optional “async” parameter.
setRequestHeader(label, value)
Adds a label/value pair to the
HTTP header to be sent.
send(content)
Sends the request.
Making Progress With Ajax
The XMLHttpRequest object
Properties
Property
Description
responseText
Returns the response as a string.
responseXML
Returns the response as XML. You can parse this DOM
tree with JavaScript.
readyState
Returns the state of the object as follows:
Onreadystatechange
status
statusText
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0 = uninitialized
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1 = open
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2 = sent
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3 = receiving
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4 = loaded
This is a reference to an event handler for an event that
fires at every change of readyState.
Returns the HTTP status code as a number (e.g. 404 for
"Not Found" and 200 for "OK").
Returns the status as a string (e.g. "Not Found" or "OK").
Demo reading file: ajax1.html
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Calling Progress Using WebSpeed
Ajax Architecture
Browser Client
Web
User
Ajax
Interface
Engine
Server
(HTML)
Documents
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Calling Progress
There are two major ways to call Progress from JavaScript
 WebSpeed
 Web Services
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Demo calling Progress: ajax3.html
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Calling Progress Using WebSpeed
WebSpeed Ajax Architecture
Browser Client
Web
User
Ajax
Interface
Engine
Server
WebSpeed
Agent
(HTML)
Documents
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Making Progress With Ajax
Database
GET or POST?
function callServer(url, targetContainer) {
var myRequest = createRequest();
var myTarget = document.getElementById(targetContainer);
myRequest.open("GET", url, false);
myRequest.send(null);
myTarget.innerHTML = myRequest.responseText;
}
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This example sends the request using GET
The parameters are appended to the URL
There is a limit of 512 bytes
In addition GET is prone to caching
Making Progress With Ajax
Switching from GET to POST
function callServer(url, data, targetContainer) {
var myRequest = createRequest();
var myTarget = document.getElementById(targetContainer);
myRequest.open("POST", url, false);
myRequest.setRequestHeader('Content-Type',
'application/x-www-form-urlencoded');
myRequest.send(data);
myTarget.innerHTML = myRequest.responseText;
}
 Change the method to POST
 Set the requestHeader to url-encoded
 Send the parameters as data
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Calling Progress using POST: ajax4.html
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Switching to XML
 Sending XML from JavaScript client:
setRequestHeader("Content-Type","text/xml");
 Receiving XML on WebSpeed server:
hDoc = WEB-CONTEXT:X-DOCUMENT.
 Sending XML from WebSpeed:
RUN outputContentType IN web-utilities-hdl
("text/xml":U).
 Receiving XML on JavaScript Client:
responseXML.firstChild.firstChild.nodeValue;
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Calling Progress using XML: ajax5.html
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Ajax Using Web Services
Advantages of Web services over WebSpeed
 Web services can be used instead of
WebSpeed
 The biggest advantage is automatic XML
conversion
 You can create Web service proxies using
ProxyGen for any .r file
 The Web Services Adapter (WSA) takes care
of the rest
 Now you have XML communication between
client and server
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Web Services and SOAP
A SOAP message is XML payload in an Envelope
Envelope
Header
Header Entry
Header Entry
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Body
Body Entry
Body Entry
…
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Demo stuff
 You have probably seen ProxyGen demos
several times
 Instead let us have a look at the generated
WSDL file
 You can install an Eclipse plug-in called Eclipse
Web Tools to help you out with Ajax
development including XML and WSDL
manipulation
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Example Using Web services: ajaxsoap.html
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Drawbacks of the Web Services Approach
 Uploading Files
• Is possible, but difficult
 Streaming data
• Not possible, you still need WebSpeed for this
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Ajax Frameworks
Why use an Ajax framework?
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Save a lot of time and effort
Do not reinvent the wheel
Mature user interface
Better quality by using a proven product
Cross-browser support
Access to widget and code libraries
Get Help and Support
Making Progress With Ajax
Examples of Ajax Frameworks
Commonly used Ajax JavaScript Frameworks
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Dojo
YUI
BackBase
SmartClient
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Dojo
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http://dojotoolkit.org
Open Source product
Very popular
Great widgets
 Not very well documented
 Prefers JSON over XML
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Yahoo! UI library
 http://developer.yahoo.com/yui
 Open Source product
 Well documented
 Very large installed base
 Easy to get started
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Backbase
 www.backbase.com
 Commercial product
 You can start with the Open Source version
 Pretty well documented
 Very powerful
 Complex
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SmartClient
 www.smartclient.com
 Commercial product
 Well documented
 Easy to get started
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?
Questions
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www.futureproofsoftware.com
[email protected]
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Thank You
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