java servlet mapping concept in web.xml file

Question

I am very new to java servlet.I am very confused about why we use servlet mapping in web.xml.I have made a project in which I have used two servlets.and if I don't use servlet mapping then also project executes in proper manner..Then why servlet mapping is used..???

Answer 1

Servlets should be registered with servlet container.For that, you should add entries in web deployment descriptor web.xml.It is located in WEB-INF directory of the web application. you have two option Either you annotation based Servlet where XMl is Not Required and once without Annotation where web.xml is required with Servlet Mapping . the mapping is defined on web.xml like

<servlet>
<servlet-name>Welcome</servlet-name>    
<servlet-class>HelloWorld</servlet-class>
</servlet>
<servlet-mapping>    
<servlet-name>Welcome</servlet-name>    
<url-pattern>/HelloWorld.do</url-pattern>
</servlet-mapping>

• Suppose on Submit any form data you want to call HelloWorld Servlet then for that servlet we have configure one unique URl that is defined as /HelloWorld.do so when you Submit the form data it will load prepspective Servlet But URL should be shown like /HelloWorld.do
• if you want to call HelloServlet from form Data then from Client code/Front end code call action ="/HelloWorld.do" full tag is <form action="action=/HelloWorld.do" method="post">
• you can call Servlet by creating servlet object as well. but suppose if you are lots of servlet file is there then unique URl pattern is required that is convient for programmer .
• Once you do login on form action call login action servlet URL and while log out call logout servlet URL .

Happy to help