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Trail: Servlets
Lesson: Running Servlets

## Configuring Tomcat Servlets

> You configure servlet application behavior by specifying elements in a text file called a Web application deployment descriptor. This file must be named `web.xml` and placed in a specific location when you install an application in Tomcat. The types of information that you specify and the format of the Web application deployment descriptor are described in the Java Servlet specification (versions 2.2 and 2.3).

> The Duke's Bookstore application uses two Web application deployment descriptor elements: `servlet` and `servlet-mapping`. All `servlet` elements must appear before any `servlet-mapping` elements.

> ## The Servlet Element

> The `servlet` element establishes a mapping between a servlet name and the fully-qualifed name of the servlet class:

>        <servlet>
>           <servlet-name>catalog</servlet-name>
>           <servlet-class>CatalogServlet</servlet-class>
>        </servlet>

> ## The Servlet Mapping Element

> When a request is received by Tomcat it must determine which servlet should handle it. You designate that certain paths (called aliases) map to a specific servlet with the `servlet-mapping` element. Alias paths appears after the context root in an HTTP request URL.

> A context root is a path that gets mapped to the document root of the servlet application. If your application's context root is `/bookstore`, then a request URL such as `http://hostname:8000/bookstore/catalog` will send the request to the servlet named `catalog` within the `bookstore` context. You set the context root and document root for an application when you configure the Tomcat server.

>        <servlet-mapping>
>           <servlet-name>catalog</servlet-name>
>           <url-pattern>/catalog</url-pattern>
>        </servlet-mapping>

> ## The Web Application Deployment Descriptor

> Here is the Web application deployment descriptor for the Duke's Bookstore example.

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