It's been a while since we touched on AJAX, but a question came up recently about it an I thought it might be good to review. AJAX, or "Asynchronous JavaScript and XML", is a way for portlet developers to create rich Web Applications that don't require the entire browser page to refresh to update content. This is done by making asynchronous calls to the server and updating content within the page itself. With the AquaLogic portal, this means that portlets can dynamically update content in <div> tags by requesting new content without having to refresh the entire page (and other portlets on the page). It's a pretty simple concept; in many cases you can accomplish this without having to even change any code - you can just specify "inline refresh" on the Web Service and the portal will automatically rewrite the HTML links on the page to make AJAX calls:
The HTML rewrites cause the browser to make the HTTP request "behind the scenes", and when a response comes back, the portal refreshes the content inside the portlet <div> tag.
But there are some things to know about this AJAX stuff, so here are a couple of refresher points about AJAX:
1) The response to an AJAX request is basically just a text string to a browser, and it's up to your JavaScript to interpret it. Often you do something like:
document.getElementById("responseDivTag").innerHTML = response.getResponse();
... to refresh content. But note that this doesn't tell the browser to "process" the response - specifically, JavaScript that comes back in the response won't run, because all we're doing is setting the HTML to a string that comes back from the server. In order to run JavaScript in the response, you should look into the JavaScript "eval()" method, which will take a string returned from the server and run it as JavaScript. Just make sure you don't include the <script> tags in your response if you really are returning JavaScript and are parsing it as such.
2) The response does not have to actually be HTML! It's just a string to the browser, and you can do anything with it. The most common use (which all of our products use) is to return JSON, or "JavaScript Object Notation", which can then be treated as objects that your script can handle however you want. Let's say you just want to know if there was a success or failure: you could literally just return a "0" or "1" in your response and write something like:
if (response.getResponseText.equals("1"))
alert("success!");
else
alert("fail");
Obviously, this just barely scratches the surface on AJAX, and you can rest assured that you haven't heard the last of it. AJAX is the cornerstone of pretty much all future Oracle portal technologies, and if you're a web developer who's not all that familiar with it, trust me: you will be soon.
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