How do you use Maven to share source code for two projects?

I have a large Java Web Application project using Maven and I need to start a new project that will share most of the same code (so I don't have to repeat work), but not all of it. I'm going to copy the shared code into a new project (let's call it "root"). How do I make my original Project depend on root for source code? I can't just jar it because I want to change the source before compiling.