Not getting automatically web.xml file while creating servlet in Eclipse Juno 4.2

I am using Eclipse Juno 4.2, Java 1.7 and Tomcat 7. But in my system when I create servlet the web.xml file doesn't create automatically, but another system it's create automatically web.xml file. I am totally confused, is there anything to configure?

I also add web.xml file when I am going to create a dynamic project.