3.3 Configure the Application Deployment Descriptor - "web.xml"
A web user invokes a servlet, which is kept in the web server, by issuing a specific URL from the browser. In this example, we shall configure the following request URL to trigger the "HelloServlet":
http://hostname:port/helloservlet/sayhello
Create a configuration file called "web.xml", and save it under "webappshelloservletWEB-INF", as follows:
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<?xml version="1.0" encoding="ISO-8859-1"?>
<web-app version="3.0"
xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd">
<!-- To save as <CATALINA_HOME>webappshelloservletWEB-INFweb.xml -->
<servlet>
<servlet-name>HelloWorldServlet</servlet-name>
<servlet-class>mypkg.HelloServlet</servlet-class>
</servlet>
<!-- Note: All <servlet> elements MUST be grouped together and
placed IN FRONT of the <servlet-mapping> elements -->
<servlet-mapping>
<servlet-name>HelloWorldServlet</servlet-name>
<url-pattern>/sayhello</url-pattern>
</servlet-mapping>
</web-app>
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- The "
web.xml" is called web application deployment descriptor. It provides the configuration options for that particular web application, such as defining the the mapping between URL and servlet class. - The above configuration defines a servlet named "
HelloWroldServlet", implemented in "mypkg.HelloServlet.class" (written earlier), and maps to URL "/sayhello", where "/" denotes the context root of this webapp "helloservlet". In other words, the absolute URL for this servlet ishttp://hostname:port/helloservlet/sayhello.
- Take note that EACH servlet requires a pair of
<servlet>and<servlet-mapping>elements to do the mapping, via an arbitrary but unique<servlet-name>. Furthermore, all the<servlet>elements must be grouped together and placed before the<servlet-mapping>elements (as specified in the XML schema).
https://www.ntu.edu.sg/home/ehchua/programming/java/JavaServlets.html