Part II: Using JavaScript to Enhance Your Pages in Java

Generation QR Code in Java Part II: Using JavaScript to Enhance Your Pages

very once in a while, a technology comes along that threatens to change everything AJAX is one such technology In this part, you learn what all the fuss is about and why AJAX is such a big deal You learn how to make your own AJAX requests by hand, and then you do some real Web 20 work with the fun and powerful jQuery library 9 describes the nuts-and-bolts details of AJAX how it works, how meaningless the acronym is, and everything See how to build an AJAX connection by hand (but after you ve seen it once, use a library like everyone else does) 10 introduces the spiffy jQuery library This free toolkit simplifies AJAX tremendously, and it adds amazing new capabilities to JavaScript Learn how to incorporate jQuery into your pages and get started with this incredible toolkit 11 shows how to use jQuery s many cool animation features You ll make various elements play hide-andseek, slide around, fade, and animate It s really fun 12 introduces the incredible jQuery user interface toolkit This fun tool allows you to create and use beautiful CSS themes You also learn how to add dragging, dropping, and resizing behavior to any element on the page 13 describes more of the jQuery user interface, especially elements that improve usability You learn how to easily build accordions and tabbed interfaces, and you are introduced to automatic calendars, sortable lists, scrollers, and custom dialogs 14 explains how jQuery helps with more advanced AJAX functions, especially working with data First you get an overview of traditional server-side programming with PHP Then you learn how AJAX simplifies this process, and how to manage data in specialized formats like XML and JSON

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Understanding AJAX Using JavaScript to manage HTTP requests Creating an XMLHttpRequest object Building a synchronous AJAX request Retrieving data from an AJAX request Managing asynchronous AJAX requests

f you ve been following the Web trends, you ve no doubt heard of AJAX This technology has generated a lot of interest Depending on who you listen to, it s either going to change the Internet or it s a lot of overblown hype In this book I show what AJAX really is, how to use it, and how to use a particular AJAX library to supercharge your Web pages

Okay, AJAX has nothing to do with a sequel to the Iliad (though that would be pretty cool) But since I have your attention, let s discuss AJAX, the mighty and very real Web technology The first thing to do is figure out exactly what AJAX is and what it isn t It isn t : A programming language Nope It isn t one more language to cram into your head (along with the many others you encounter) New No Most of the technology in AJAX isn t really all that new It s the way it s being used that s different Remarkably different Not really For the most part, AJAX is really the same kinds of things you see in the rest of this book It s about building compliant Web pages that interact with the user

So you ve got to wonder why people are so excited about AJAX It s a relatively simple thing, but it has the potential to change the way people think about Internet development Here s what it really is, has, and does: Direct control of client-server communication Rather than relying on the automatic communication between client and server that happens with Web sites and server-side programs, AJAX is about managing this relationship more directly Use of the XMLHttpRequest object This is a special object that s been built into the DOM of all major browsers for some time, but hasn t been used heavily The real innovation of AJAX was finding creative (perhaps unintentional) uses for this heretofore-obscure utility A closer relationship between client-side and server-side programming Up to now, client-side programs (usually JavaScript) did their own thing, and server-side programs (PHP) operated without too much knowledge of each other AJAX helps these two types of programming work together better A series of libraries that facilitate this communication AJAX isn t all that hard to use, but it does have a lot of details Several great libraries have sprung up to simplify using AJAX technologies You ll find AJAX libraries for both client-side languages (like JavaScript) and server-side languages (like PHP) As an added bonus, these libraries often include other great features that make JavaScript programming easier and more powerful Let s say you re making an online purchase with a shopping-cart mechanism In a typical (pre-AJAX) system, an entire Web page is downloaded to the user s computer There might be a limited amount of JavaScript-based interactivity, but anything that requires a data request needs to be sent back to the server For example, if you re on a shopping site and you want more information about that fur-lined fishbowl you ve had your eye on, you might click the More information button Doing so sends a request to the server, which builds an entire new Web page for you, containing your new request Every time you make a request, the system builds a whole new page on the fly The client and server have a long-distance relationship In the old days when you wanted to manage your Web site s content, you had to refresh each Web page time-consuming to say the least But with AJAX, you can update the content without refreshing the page Instead of the server sending an entire-page response just to update a few words, the server only sends the words you want to update and nothing else