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6

Chapter 1 Overview of Servlets and JavaServer Pages

3. Generate the results. 

This process may require talking to a database, executing an 

RMI or CORBA call, invoking a legacy application, or comput 

ing the response directly.

4. Format the results inside a document. 

In most cases, this involves embedding the information inside 

an HTML page.

5. Set the appropriate HTTP response parameters. 

This means telling the browser what type of document is being 

returned (e.g., HTML), setting cookies and caching parameters, 

and other such tasks.

6. Send the document back to the client. 

This document may be sent in text format (HTML), binary for 

mat (GIF images), or even in a compressed format like gzip that 

is layered on top of some other underlying format.

Many client requests can be satisfied by returning pre built documents,

and these requests would be handled by the server 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 like this:

The Web page is based on data submitted by the user. 

For instance, the results page from search engines and 

order confirmation pages at on line stores are specific to 

particular user requests.

The Web page is derived from data that changes 

frequently. 

For example, a weather report or news headlines page might 

build the page dynamically, perhaps returning a previously built 

page if it is still up to date. 

The Web page uses information from corporate 

databases or other server side sources. 

For example, an e commerce site could use a servlet to build a 

Web page that lists the current price and availability of each 

item that is for sale. 

In principle, servlets are not restricted to Web or application servers that

handle HTTP requests, but can be used for other types of servers as well. For

Second edition of this book: www.coreservlets.com; Sequel: www.moreservlets.com.

Servlet and JSP training courses by book's author: courses.coreservlets.com.