Question: I have different webapps that share a large portion of the web.xml configuration. For example, the way some servlets are mapped is identical for all apps, but some webapps have custom servlets, or an additional filter, or shared managed beans.

Each webapp is a different project in my IDE. I would like to refactor the common part of my web.xml to a "common" project, and let all the application-specific web.xml's extend the "common" web.xml. Is there any possibility to do this?

Answer: 
If you deploy your apps on glassfish, than you can put your common configuration in `default-web.xml` file under the `domain-dir\config\` location.
Usually web servers have feature to define default web.xml which caters to your requirement. I would suggest to explore that option for the web server you are using.