An Overview of Servlet and JSP Technology
Nagle and Wiegley，Aug. 2008，953 – 958.
Abstract: Servlet program running in the server-side, dynamically generated Web page
with the traditional CGI and many other similar compared to CGI technology, Java Servlet
with a more efficient, easier to use, more powerful and has better portability, more savings
to invest .
Key words: JSP Technology, Servlet, HTTP server
1.1 A Servlet's Job
Servlets are Java programs that run on Web or application servers, acting as a middle
layer between requests coming from Web browsers or other HTTP clients and databases or
applications on the HTTP server. Their job is to perform the following tasks, as illustrated
in Figure 1-1.
Figure 1-1
1．Read the explicit data sent by the client.
The end user normally enters this data in an HTML form on a Web page. However,
the data could also come from an applet or a custom HTTP client program.
2．Read the implicit HTTP request data sent by the browser.
Figure 1-1 shows a single arrow going from the client to the Web server (the layer
where servlets and JSP execute), but there are really two varieties of data: the explicit data
that the end user enters in a form and the behind-the-scenes HTTP information. Both
varieties are critical. The HTTP information includes cookies, information about media
types and compression schemes the browser understands, and so on.
3．Generate the results.
This process may require talking to a database, executing an RMI or EJB call,
invoking a Web service, or computing the response directly. Your real data may be in a
relational database. Fine. But your database probably doesn't speak HTTP or return results
in HTML, so the Web browser can't talk directly to the database. Even if it could, for
security reasons, you probably would not want it to. The same argument applies to most
other applications.You need the Web middle layer to extract the results
inside a document.
4．Send the explicit data (i.e., the document) to the client.
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