J2EE Design Patterns

Chapter 5. Presentation Tier Scalability

Many developers believe design patterns and scalability do not go hand in hand. They argue that patterns add layers to an application, so the server must perform more operations and use more memory to handle each request. The extra operations slow response time down, and the increase in memory means fewer clients can be supported per server. By itself, this is a fair assessment, and if no two requests were alike, it might be the end of the story.

In an enterprise application, however, many clients need to access similar data. On a site that publishes stock quotes, for example, the server may respond to thousands of requests a minute for the same stock. If the price of the stock changes every five minutes, it would be massively inefficient to contact the stock market for each request. Even in an online bank, where every user wants to view personal data, resources such as database connections do not need to be recreated for every request.

Often, we can sacrifice some speed up front for better performance in the average case. While the first request for a particular stock quote or the first connection to a particular database might require a lot of work, subsequent requests will be much faster. It is fair to say the system’s scalability will increase: we can support more requests in the same amount of time.

In this chapter, we look at three patterns that increase the scalability of the presentation tier using variations of this concept:

Asynchronous ...