The meaning of this is that in our login.jsp we have written action=servlet/com.onjava.login.
This same string "servlet/com.onjava.login" has to appear in web.xml in url-pattern. You can write any string but has to be same in jsp and in xml e.g. you can have string "Good", no problem.

The string between <servlet-mapping> and between
<servlet-name> has to be same, here it is login.
Then finally :) the string between <servlet-class> is the actual class part for your FILE login.class i.e. com.onjava.login. :)
web.xml->
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<web-app>
<servlet>

<servlet-name>login</servlet-name>
<servlet-class>com.onjava.login</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>login</servlet-name>
<url-pattern>servlet/com.onjava.login</url-pattern>
</servlet-mapping>

</web-app>
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