The "web.xml" is called web application deployment descriptor

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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>

  • 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 is  http://hostname:port/helloservlet/sayhello.
    The &quot;web.xml&quot; is called web application deployment descriptor

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  • 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

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