JavaServer Pages, 3rd Edition

Caching Data

Before we look at the <x:parse> action in detail, I’d like to say a few words about the caching technique used in this example. The Meerkat data is updated only on an hourly basis, so it’s pointless to ask for it more frequently. It’s also expensive in terms of time and computing resources to import and parse the XML data. By caching the parsed data for an hour, the web application gets more responsive and avoids putting load on the Meerkat server unnecessarily.

The caching technique used here simply creates a timestamp for the data in the form of a java.util.Date object and saves it together with the data itself in the application scope, using standard and JSTL core actions. When a new request is received, it’s tested to see if the cache is older than the predefined cache period (one hour in this example). If it is, a fresh copy is imported, parsed, and saved in the application scope again, along with the timestamp. Otherwise the cached data is used. You can use this technique for any type of processing that’s expensive, for instance retrieving data from a database or performing complex calculations.