Facelets (https://facelets.dev.java.net) is a framework that provides an alternative view technology to JSP, and is one of the supported view technologies of Seam. Seam 2.1 introduced support for Apache Wicket (http://wicket.apache.org) as a Seam view technology, but that is not covered in this book.
With JSP, suppose that a client requests a page from the server. The first time this page is accessed, it is converted into a servlet. This servlet is then responsible for generating the HTML that is returned to the client.
Java Server Faces works in a different manner, by building up a tree of components that are rendered to the view as necessary (note that JSF does not necessarily have to render HTML). Each JSF page has a life cycle consisting of several stages, as shown in the following diagram. Facelets is responsible for managing the Restore View and Render Response phases within the JSF life cycle.