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Web XML

layout: default title: web.xml Configuration File

web.xml is written in XML, eXtensible Markup Language.

XML is like HTML, but it allows users to define their own customized tags. * Applications can read these tags and determine what to do with the data based on the tag.

web.xml Explained

Sun Microsystems, the company that owned Java before Oracle, defined the XML tags used in web.xml.

<?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" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" version="3.0">
  <display-name>JavaWebIntro</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
  </welcome-file-list>
  <servlet>
    <servlet-name>helloWorld</servlet-name>
    <servlet-class>com.example.javaweb.examples.HelloWorldServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>helloWorld</servlet-name>
    <url-pattern>/hello</url-pattern>
  </servlet-mapping>

  <servlet>
    <servlet-name>inventory</servlet-name>
    <servlet-class>com.example.javaweb.labs.InventoryServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>inventory</servlet-name>
    <url-pattern>/inventory</url-pattern>
  </servlet-mapping>
</web-app>

<welcome-file-list> - This is a list of files that will display when the user does not request a particular page. The list is ordered, and the application will display the first file it finds.

<servlet> - The servlet is configured here to handle requests. * <servlet-name> - The servlet has an arbitrary name. * <servlet-class> - The fully-qualified Java Servlet class.

<servlet-mapping> - This tag is how the web container knows to send requests to URLs to a certain servlet class for handling. * <servlet-name> - this must match the servlet-name of a <servlet> (above); that is the connection between a Java class and a URL. * <url-pattern> - this maps a request for a resource to this servlet. * For example, to match all requests for resources ending in .do to a servlet, use <url-pattern>*.do</url-pattern>.

Example: Following a Request from Page to Servlet

In this example we will examine the link:

<a href="hello">Access Hello Servlet</a>

which creates this request:

GET http://localhost:8080/JavaWebIntro/hello

  • localhost:8080 is the URL for Tomcat.

  • JavaWebIntro is the context path. This tells Tomcat which web application should try and handle the request.

localhost and context path

The requested URL hello is mapped to <url-pattern>/hello</url-pattern>. * This pattern is mapped to the servlet named helloWorld, which uses the HelloWorldServlet Java class.

url-pattern to servlet-class

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