Introduction to Java Server Pages

Introduction to Java Server Pages

In late 1999, Sun Micro systems added a new element to the collection of Enterprise Java tools: Java Server Pages (JSP). Java Server Pages are built on top of Java servlets and designed to increase the efficiency in which programmers, and even non programmers, can create web content.

Java Server Pages is a technology for developing web pages that include dynamic content. Unlike a plain HTML page, which contains static content that always remains the same, a JSP page can change its content based on any number of variable items, including the identity of the user, the user's browser type, information provided by the user, and selections made by the user.

What Is JavaServer Pages?

A JSP page contains standard markup language elements, such as HTML tags, just like a regular web page. However, a JSP page also contains special JSP elements that allow the server to insert dynamic content in the page. JSP elements can be used for a variety of purposes, such as retrieving information from a database or registering user preferences. When a user asks for a JSP page, the server executes the JSP elements, merges the results with the static parts of the page, and sends the

dynamically composed page back to the browser.

JSP defines a number of standard elements that are useful for any web application, such as accessing JavaBeans components, passing control between pages and sharing information between requests, pages, and users. Developers can also extend the JSP syntax by implementing application-specific elements that perform tasks such as accessing databases and Enterprise JavaBeans, sending email, and generating HTML to present application-specific data. One such set of commonly needed custom elements is defined by a specification related to the JSP specification: the JSP Standard Tag Library (JSTL) specification. The combination of standard elements and custom elements allows for the creation of powerful web applications.

Why Use JSP?

In the early days of the Web, the Common Gateway Interface (CGI) was the only tool for developing dynamic web content. However, CGI is not an efficient solution. For every request that comes in, the web server has to create a new operatingsystem process, load an interpreter and a script, execute the script, and then tear it all down again. This is very taxing for the server and doesn't scale well when the amount of traffic increases.

Numerous CGI alternatives and enhancements, such as FastCGI, mod_perl from Apache, NSAPI from Netscape, ISAPI from Microsoft, and Java servlets from Sun Microsystems, have been created over the years. While these solutions offer better performance and scalability, all these technologies suffer from a common problem: they generate web pages by embedding HTML directly in programming language code. This pushes the creation of dynamic web pages exclusively into the realm of programmers. JavaServer Pages, however, changes all that.

The JSP Advantage

JSP combines the most important features found in the alternatives:

• JSP supports both scripting- and element-based dynamic content, and allows developers to create custom tag libraries to satisfy application-specific needs.

• JSP pages are compiled for efficient server processing.

• JSP pages can be used in combination with servlets that handle the business logic, the model favored by Java servlet template engines.

In addition, JSP has a couple of unique advantages that make it stand out from the crowd:

• JSP is a specification, not a product. This means vendors can compete with different implementations, leading to better performance and quality. It also leads to a less obvious advantage, namely that when so many companies have invested time and money in the technology, chances are it will be around for a long time, with reasonable assurances that new versions will be backward compatible; with a proprietary technology, this is not always a given.

• JSP is an integral part of J2EE, a complete platform for enterprise class applications. This means that JSP can play a part in the simplest applications to the most complex and demanding.

What You Need to Get Started

Before we begin, let's quickly run through what you need to run the examples and develop your own applications. You really only need three things:

• A PC or workstation, with a connection to the Internet so you can download the software you need

• A Java 2 compatible-Java Software Development Kit (Java 2 SDK)

• A JSP 2.0-enabled web server, such as Apache Tomcat from the Jakarta Project