J2EE Design Patterns

Content Caching

One of the best ways to increase scalability is through caching. Caching static pages is a well established practice on the web, and dedicated web caches are taking their place with routers and switches as standard equipment in the data center. A web cache maintains copies of the most frequently requested files, which allows it to serve those requests quickly, without involving the real web server. Most caches rightly ignore dynamically generated pages, as there’s no way to efficiently determine whether any two requests should receive the same response (or, for that matter, whether the web server needs to process the request for other reasons).

To create a high performance J2EE environment, we need to bring the benefits of caching to the dynamic components of the presentation tier. In this section, we’ll look at two approaches to this problem: caching the input used to generate the dynamic content, and caching the generated content itself.

Caching Content Components

The traditional communication model for web applications is synchronous . In other words, clients make requests for URLs and wait until they receive a web page in response. Given the nature of this exchange, it is easy to see why most application logic is implemented in a synchronous manner. As requests come in, the various parts of the response are calculated and correlated, and then the final response is generated. The problem with this approach is that it can be quite inefficient.

In Chapter 4 we discussed ...