Jetty is a 100% Java HTTP Server and Servlet Container. This means that you do not need to configure and run a seperate web server (like Apache) in order to use java, servlets and JSPs to generate dynamic content. Jetty is a fully featured web server for static and dynamic content. Unlike separate server/container solutions, this means that your web server and web application run in the same process, without interconnection overheads and complications. Furthermore, as a pure java component, Jetty can be simply included in your application for demonstration, distribution or deployment. Jetty is available on all Java supported platforms.
You can also visit Jetty's Javadoc