Search for text in all repos

I would like to be able to search for a specific piece of text in all files, in all projects, through a repository (even all repositories).

The latest version of the master branch of each project would a good enough candidate, for starters.

Of course, the more search criteria, the better (like excluding repos/projects or searching through specific branches of projects).

My use-case : I want to search where (which project and in what files) a java class from one project is being used (it might be used as Spring bean and declared in an xml file)