.do web page extension

A web page with extension '.do' what type of file is this? A web server can be setup to use any extension for any type of files so '.do' can be any kind of file. 

Java based web applications that use the struts framework use this extension. Struts uses a config file to map an incoming request to a Java class on the server side that does the processing, a struts request shoud have the extension ".do"