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2024年3月12日发(作者：shell脚本dirname)
An Overview of Servlet and JSP Technology
Nagle ,Wiegley
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. .
Keywords: JSP Technology;Servlet;HTTP server
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 Web middleware role
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.
1.2 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.
1.3 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 need the Web middle layer to
extract the results inside a document.
1.4 Send the explicit data (i.e., the document) to the client.
This document can be sent in a variety of formats, including text (HTML or
XML), binary (GIF images), or even a compressed format like gzip that is layered on
top of some other underlying format. But, HTML is by far the most common
format, so an important servlet/JSP task is to wrap the results inside of HTML.
1.5 Send the implicit HTTP response data.
Figure 1-1 shows a single arrow going from the Web middle layer (the servlet
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