Web.xml file

Web.xml file
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While doing a web application and after creating a Servlet we will need to create a deployment descriptor (DD) named web.xml. We will find in that file XML’s code that we don’t understand the meaning. It is called Servlet Mapping. Those codes will look like:

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
  <display-name>ServletTest</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  <servlet>
    <description></description>
    <display-name>Ch1Servlet</display-name>
    <servlet-name>Ch1Servlet</servlet-name>
    <servlet-class>com.servlet.test.Ch1Servlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>Ch1Servlet</servlet-name>
    <url-pattern>/Ch1Servlet</url-pattern>
  </servlet-mapping>
  
  <servlet>
  	<servlet-name>Ch2Dice</servlet-name>
  	<servlet-class>com.servlet.test.Ch2Dice</servlet-class>
  </servlet>
  <servlet-mapping>
 	<servlet-name>Ch2Dice</servlet-name> 
 	<url-pattern>/Ch2Dice</url-pattern>
  </servlet-mapping>
</web-app>

The mapping will improve the application flexibility, while we need to make some changes we won’t need to inform everyone about the changes, and improve the security because the user name won’t be able to know the way our server is structured, he could find files without going through the right pages or forms.

The code between <Servlet></Servlet> maps the internal name to fully-qualified class name
The code between <Servlet-mapping></Servlet-mapping> maps the internal name to public URL name which means the path which will be seen by the user and which is in most of time coded.