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Intro to Ajax

Intro to Ajax. Fred Stluka Jan 25, 2006. What is Ajax?. "Asynchronous JavaScript and XML" New name for an old technique: JavaScript + DHTML + XMLHttpRequest In use since at least 1997 I've used it since 2000 Finally someone gave it a name Already enabled in your Web server and browser

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Intro to Ajax

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  1. Intro to Ajax Fred Stluka Jan 25, 2006

  2. What is Ajax? • "Asynchronous JavaScript and XML" • New name for an old technique: • JavaScript + DHTML + XMLHttpRequest • In use since at least 1997 • I've used it since 2000 • Finally someone gave it a name • Already enabled in your Web server and browser • Use JavaScript asynchronously behind the scenes to load additional data (typically XML) without discarding and reloading the entire Web page. Intro to Ajax Fred Stluka

  3. Why use Ajax? • Your users will soon demand it • Not just another cool (geeky) technology • Very user-visible effect • Rich UI experience in a Web page • Portable across browsers • Plus, all advantages of zero-install Web app • No install done for this demo • No "DLL Hell" Intro to Ajax Fred Stluka

  4. Why use Ajax? • Client/Server Apps: • Dynamic data • Static forms, controls, code, etc. • Efficient, but not flexible • Traditional Web Apps: • Dynamic data • Dynamic forms, controls, code, etc. • Flexible, but inefficient, and noticeably slow • Ajax Apps: • Dynamic data • Static or dynamic forms, controls, code, etc. • Best of both worlds Intro to Ajax Fred Stluka

  5. Why use Ajax? • Geeky reasons: • Multithreaded data retrieval from Web servers • Pre-fetch data before needed • Progress indicators • Appearance of speed • Avoids need for setTimeout() • Less bandwidth required; less server load • Reload partial page, not entire page • Load data only, not even partial page Intro to Ajax Fred Stluka

  6. How much to use Ajax? • As little or as much as you like • No need to abandon what you already do • One more item in your "bag of tricks" • Start by jazzing up your existing UI Intro to Ajax Fred Stluka

  7. How to use Ajax? Simple! Use the XMLHttpRequest Object Intro to Ajax Fred Stluka

  8. XMLHttpRequest Methods • open (“method”, “URL”, [async, username, password]) • Assigns destination URL, method, etc. • send (params) • Sends request including postable string or DOM object data • abort () • Terminates current request • getAllResponseHeaders () • Returns headers (name/value pairs) as a string • getResponseHeader (“header”) • Returns value of a given header • setRequestHeader (“label”,”value”) • Sets Request Headers before sending Intro to Ajax Fred Stluka

  9. XMLHttpRequest Properties • onreadystatechange • Event handler (your code) that fires at each state change • readyState 0 = uninitialized 3 = interactive (some data has been returned) 1 = loading (broken in IE 6.0) 2 = loaded 4 = complete • status • HTTP Status returned from server: 200-299 = OK • responseText • String version of data returned from server • responseXML • XML DOM document of data returned • statusText • Status text returned from server Intro to Ajax Fred Stluka

  10. Simple Example var req = new XMLHttpRequest(); req.onreadystatechange = myHandler; req.open("GET", "servlet", true); req.send("p1=abc"); ... function myHandler() { if (req.readyState == 4) { doSomethingWith(req.responseXML); } else if (req.readyState == 3) { showProgressIndicator(); } } Intro to Ajax Fred Stluka

  11. Demos • http://bristle.com/~fred/#ajax • Simple demo • More demos • Google Suggest • Google Maps • Language translation • Mouse gesture as password • Typing speed as password • Classified ads tied to map • "Mashups" Intro to Ajax Fred Stluka

  12. Security Issues • Can only hit domain the Web page came from • Cannot access a 3rd party Web Service • However: • You can wrap those requests through your own server • User can allow access to specific sites via browser security settings • IFRAME can access any site (instead of XMLHttpRequest) Intro to Ajax Fred Stluka

  13. Advanced Topics • http://bristle.com/~fred/#ajax • XSLT and XPath support (Sarissa) • Serializing Java Beans as XML • XMLBeans, JAXB, Zeus, Jbind, Castor, Betwixt • Serializing Java Beans as JavaScript objects • JSON -- JavaScript Object Notation • 2-way Mapping of Java Beans to JavaScript objects • DWR -- Direct Web Remoting • Ajax Component Libraries and Toolkits: • Dojo, Prototype, HTC, XBL • Implemented as JSP tag libraries or pure JavaScript • Ajax Frameworks • Ajax Patterns Intro to Ajax Fred Stluka

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