Servlets and JSP (Java Server Pages) are the main way that Java is used in the Web today. These are Java programs that run on a Web server that allow HTML content to be dynamically generated (often by querying a database) and then sent via the web to a ""client"" machine that made the request in the first place. Jorelids book concentrates on teaching the program architect and designer how to fit the various pieces together, spending as little time as possible on the mechanics of coding.
As the tech reviewer puts it, ""Jorelids perspective is unique and not voiced in any of the popular Servlet books (such as the ones by Jason Hunter, Marty Hall, Calloway, etc). The code examples in the touring the package sections nicely explain how to use the important methods in the Servlet API. I have yet to see any existing books get into these useful details.""