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ABOUT JAVA TECHNOLOGY

Servlets and JSP: An Overview

1. What are Java Servlets?

Servlets are Java technology's answer to CGI programming. They are programs

that run on a Web server and build Web pages. Building Web pages on the fly is

useful (and commonly done) for a number of reasons:

� The Web page is based on data submitted by the user. For example the results

pages from search engines are generated this way, and programs that process

lists current prices and number of items in stock.

2. What are the Advantage of Servlets Over "Traditional" CGI?

Java servlets are more efficient, easier to use, more powerful, more portable, and

cheaper than traditional CGI and than many alternative CGI-like technologies. (More

importantly, servlet developers get paid more than Perl programmers :-).

� Efficient. With traditional CGI, a new process is started for each HTTP request. If

the CGI program does a relatively fast operation, the overhead of starting the process

can dominate the execution time. With servlets, the Java Virtual Machine stays up,

and each request is handled by a lightweight Java thread, not a heavyweight operating

system process. Similarly, in traditional CGI, if there are N simultaneous request to

convenience of being able to use a familiar language, servlets have an extensive

infrastructure for automatically parsing and decoding HTML form data, reading and

setting HTTP headers, handling cookies, tracking sessions, and many other such

utilities.

� Powerful. Java servlets let you easily do several things that are difficult or

impossible with regular CGI. For one thing, servlets can talk directly to the Web

server (regular CGI programs can't). This simplifies operations that need to look up

images and other data stored in standard places. Servlets can also share data among

each other, making useful things like database connection pools easy to implement.

They can also maintain information from request to request, simplifying things like

available that are good for "personal" use or low-volume Web sites. However, with

the major exception of Apache, which is free, most commercial-quality Web servers

are relatively expensive. Nevertheless, once you have a Web server, no matter the cost

of that server, adding servlet support to it (if it doesn't come preconfigured to support

servlets) is generally free or cheap.

3. What is JSP?

Java Server Pages (JSP) is a technology that lets you mix regular, static HTML

with dynamically-generated HTML. Many Web pages that are built by CGI programs

are mostly static, with the dynamic part limited to a few small locations. But most

CGI variations, including servlets, make you generate the entire page via your

<!-- User name is "New User" for first-time visitors -->

To access your account settings, click

<A HREF="Account-Settings.html">here.</A></SMALL>

<P>

Regular HTML for all the rest of the on-line store's Web page.

</BODY></HTML>

� vs. Active Server Pages (ASP). ASP is a similar technology from Microsoft. The

advantages of JSP are twofold. First, the dynamic part is written in Java, not Visual

Basic or other MS-specific language, so it is more powerful and easier to use. Second,

it is portable to other operating systems and non-Microsoft Web servers.

� vs. Pure Servlets. JSP doesn't give you anything that you couldn't in principle do

� vs. Server-Side Includes (SSI). SSI is a widely-supported technology for

including externally-defined pieces into a static Web page. JSP is better because it lets

you use servlets instead of a separate program to generate that dynamic part. Besides,

SSI is really only intended for simple inclusions, not for "real" programs that use form

submission data is not available to JavaScript. And, since it runs on the client,

JavaScript can't access server-side resources like databases, catalogs, pricing

information, and the like.

JSP is so easy and convenient that it is quite feasible to augment HTML pages that

only benefit marginally by the insertion of small amounts of dynamic data. Previously,

the cost of using dynamic data would preclude its use in all but the most valuable

instances.

Overview

JavaServer Pages (JSP) lets you separate the dynamic part of your pages from

the static HTML. You simply write the regular HTML in the normal manner, using

whatever Web-page-building tools you normally use. You then enclose the code for

the dynamic parts in special tags, most of which start with "<%" and end with "%>".

For example, here is a section of a JSP page that results in something like "Thanks for

ordering Core Web Programming"for URL of

http://host/OrderConfirmation.jsp?title=Core+Web+Programming:

Thanks for ordering a

<I><%= request.getParameter("title") %></I>