This chapter provides a quick introduction to some of the things an HTTP servlet can do. For example, an HTTP servlet can generate an HTML page, either when the servlet is accessed explicitly by name, by following a hypertext link, or as the result of a form submission. An HTTP servlet can also be embedded inside an HTML page, where it functions as a server-side include. Servlets can be chained together to produce complex effects—one common use of this technique is for filtering content. Finally, snippets of servlet code can be embedded directly in HTML pages using a new technique called JavaServer Pages.
Although the code for each of the examples in this chapter is available for download (as described in the the preface), we would suggest that for these first examples you deny yourself the convenience of the Internet and type in the examples. It should help the concepts seep into your brain.
Don’t be alarmed if we seem to skim lightly over some topics in this chapter. Servlets are powerful and, at times, complicated. The point here is to give you a general overview of how things work, before jumping in and overwhelming you with all of the details. By the end of this book, we promise that you’ll be able to write servlets that do everything but make tea.
Before we can even show you a simple HTTP servlet, we need to make sure that you have a basic understanding of how the protocol behind the Web, HTTP, works. If you’re an experienced CGI programmer ...