Error assembling WAR: webxml attribute is required (or pre-existing WEB-INF/web.xml maven on war

You might come across this error when building a web application on maven using the command

mvn war:war

This would be caused if maven is not aware of where the web.xml file is located.
If you follow the standard maven directory structure as


You would have to copy the contents of WebContent [WEB-INF AND META-INF] to src/main/webapp folder – there maven would get it as expected.