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An AJAX Caching Strategy
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05/04/2006, By Bruce Perry
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Over xml.com, Bruce Perry has written an article on AJAX Caching Strategy.
Making HTTP requests willy-nilly from AJAX applications, however, is almost never a good idea or design decision. The server side of the equation may not be able to handle the flood of requests. The client side of the AJAX application may have some of its requests time out or abort, which will disrupt the user experience that is meant to be AJAX's strength.
Specify a Time Period for Caching Data
There are always a number of viable solutions to such a problem or requirement. The one I chose was to create an object, using the Prototype open source JavaScript library, that keeps track of when a price was last updated by an HTTP request. The object has a property that represents a range, say 24 hours. If the price was fetched less than 24 hours ago, then the object prevents a new request from being initiated and keeps the displayed price the same.
This is an AJAX caching strategy that is designed to periodically refresh data from a server, but only if the client's version of the data has been cached for a specified period. If the application user leaves the page in her browser for more than 24 hours, then clicks a Refresh button, XHR goes out and grabs a new price for display. We want to give the user the ability to refresh the price without reloading the entire application into the browser, yet we also want to cut down on unnecessary requests.
The server component can be written in your language of choice for scraping web-page information: PHP, Ruby, Python, ASP.NET, Perl, Java. I chose Java, being partial to servlet/JSP programming and the Tomcat container. The Ajax.Request object connects with a JSP, which uses Java utility classes to harvest the energy information from U.S. EIA sites.
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