Chapter 7: Filters

---

Overview

The Servlet 2.3 specification introduces a new type of web application component - filters. Filters allow us to add functionality to our web applications that previously would have required proprietary container enhancements or other non-portable extensions to our environment. Filters sit between the client and the underlying web application, and are used to examine and modify the requests and responses that flow between them.

We can use filters to quickly prototype new concepts, or to add new functionality to our applications - without having to alter the original application.

In this chapter, we will:

• Discover what a filter is, and understand how they fit into the logical and physical design of our web applications.

• Look at how filters can be configured and combined together at deployment time

Along the way, we will design and code two practical filters that can be used to log access to our applications, and to transform content for different types of clients.

---