Currently there exists a need to create an application that will serve 5 different customers each requiring their own specific URL and content repository. My question is when designing this application what should my considerations be for protecting the content of the individual customers while meeting the requirements of the unique URL. The system will be sitting on Windows with a postgres database and java as the implementation language.
I'm not sure I understand to the following :
each requiring their own specific URL
x
meeting the requirements of the unique URL
But I sense what you want to do. The fact that there would be 5 groups/communities of users makes the application quite complicated. You are not explaining yourself much so I can refer to Liferay portal, which practically implements everything you need : user/group management and content repository.
If you don't mind that it is a portlet container, then developing a simple portlet that handles various groups of users that operate on content repository of various resources, could be much easier than programming it from scratch. It's all done, you just set it up.