Chapter 10. The Wrapper Component
We are finally at the workhorse of the Tomcat component hierarchy—the Wrapper. This unassuming component is what breathes life into your servlets, and consequently is a very critical component to a web developer.
In the default case, where Tomcat is not running in a clustered configuration, the container is expected to use only one servlet instance per<servlet> element in the web deployment descriptor. It is this single instance that is wrapped by a Wrapper component.
The servlet specification requires each servlet to implement the javax.servlet.Servlet interface, which defines the init(), service(), and destroy() life cycle methods. The primary role of a Wrapper component is to invoke these methods at appropriate times in the lifetime of a servlet instance.
When a servlet implements the SingleThreadModel interface, the Wrapper might actually manage a pool of servlet instances, while ensuring that only one thread is executing within a servlet instance...
