How do I run a servlet from command-line mode?

Once you install your servlet inside a servlet container like Tomcat, you can fetch the results of the servlet by using a command-line tool like wget or curl (or write your own HTTP client -- it's not very difficult).

You can also use a tool like ServletUnit (part of HTTPUnit) that's a "bare-bones" on-the-spot servlet runner. Be warned, though; it doesn't implement all the features.