What you're looking to use are our "Project Archives" tools. You can start by opening the Project Archives view, then in the Package Explorer, select your project.
Then back in the Project Archives view, right-click your project, and create a new jar configuration. You can add folders or filesets to this. It is built incrementally after workspace changes and is very fast, but may take a little while to get used to.
It can also be easily deployed to a server. ;)