Web Server: Static Files
From Resin 4.0 Wiki
Sending static files quickly is an key feature of the Resin Web Server. While the dynamic content take more development time, all the small images, css files, and the javascript needs to arrive at the browser quickly to ensure a responsive site.
sendfile()
Resin's static file serving is fast and efficient with the operating system sendfile() support. Large files are sent directly from the file system to the HTTP socket by the operating system, minimizing Java overhead.