However, although the Java TM platform is independent, the Web as a whole is not. To handle such issues, Thomas Davis and Craig Walker have developed an unobtrusive framework, an invisible layer between your servlets and the servlet engine, that gives you greater control over the environment. The ubiquitous servlet flourishes in all areas of Web development.
Authors devote entire books to servlets.
If you are a Java fanatic, and your project has a Web interface, you use servlets. Servlets are a simple concept, and the Java TM Servlet API reflects that. And a Session object stores any stateful data that needs to persist between the handshakes. The flow of information in a servlet Sun's Java Servlet API does an excellent job of hiding all the dirty work from the programmer, leaving the servlet engine to manage it instead. However, the programmer occasionally needs to peek behind the curtain and twiddle the knobs.