1.2 Why Build Web Pages Dynamically?
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J2EE training from the author: http://courses.coreservlets.com/
1.2 Why Build Web
Pages Dynamically?
After Marty wrote the first edition of Core Servlets and JavaServer Pages, various of
his non-software-savvy friends and relations would ask him what his book was about.
Marty would launch into a long, technical discussion of Java, object-oriented pro-
gramming, and HTTP, only to see their eyes immediately glaze over. Finally, in exas-
peration, they would ask, “Oh, so your book is about how to make Web pages, right?”
“Well, no,” the answer would be, “They are about how to make programs that
make Web pages.”
“Huh? Why wait until the client requests the page and then have a program build
the result? Why not just build the Web page ahead of time?”
Yes, many client requests can be satisfied by prebuilt documents, and the server
would handle these requests without invoking servlets. In many cases, however, a
static result is not sufficient, and a page needs to be generated for each request.
There are a number of reasons why Web pages need to be built on-the-fly:
• The Web page is based on data sent by the client.
For instance, the results page from search engines and order-
confirmation pages at online stores are specific to particular user
requests. You don’t know what to display until you read the data that
the user submits. Just remember that the user submits two kinds of
data: explicit (i.e., HTML form data) and implicit (i.e., HTTP request
headers). Either kind of input can be used to build the output page. In
particular, it is quite common to build a user-specific page based on a
cookie value.
• The Web page is derived from data that changes frequently.
If the page changes for every request, then you certainly need to build
the response at request time. If it changes only periodically, however,
you could do it two ways: you could periodically build a new Web page
on the server (independently of client requests), or you could wait and
only build the page when the user requests it. The right approach
depends on the situation, but sometimes it is more convenient to do
the latter: wait for the user request. For example, a weather report or
news headlines site might build the pages dynamically, perhaps
returning a previously built page if that page is still up to date.
• The Web page uses information from corporate databases or
other server-side sources.
If the information is in a database, you need server-side processing
even if the client is using dynamic Web content such as an applet.
Imagine using an applet by itself for a search engine site:
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wzbyytm2013-10-01对servlet的介绍很全面，例子简介，精炼。尤其是关于cookie，监听器和拦截器的介绍很到位。
liangtai2013-04-01Wanderful JSP/Servlet material.
