In this chapter, we will discuss two similar technologies: valves and filters. These technologies were invented for the purpose of intercepting requests for one or more web applications. The first, Tomcat Valve, is a proprietary Tomcat technology. The second, servlet filters, is a server-independent technology that was introduced as part of the Java Servlet specification (since version 2.3). Both of these technologies are used to process HTTP requests and response objects.
We will cover the following: