Deployment descriptor file which is also known as web.xml file, is used to configure the web app as well as servlet.
It is most important while the web app is to be deployed on the server, for example the database connection is going to differ while you deploy the app on server, so its preferable to define such settings in web.xml file because its a tag file which can be easily editable in any editor.
If we define the such settings in java file they need to be edited and re-compile on server, which is not feasible.
OS : Windows 10
Jdk : Version 8
IDE : Eclipse Mars
Server : Apache Tomcat 7
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