Introduction

In Chapter 26, you learned how to generate dynamic Web pages with servlets. You probably have already noticed in our examples that most of the code in our servlets generated output that consisted of the HTML elements that composed the response to the client. Only a small portion of the code dealt with the business logic. Generating responses from servlets requires that Web application developers be familiar with Java. However, many people involved in Web application development, such as Web site designers, do not know Java. It is difficult for people who are not Java programmers to implement, maintain and extend a Web application that consists of primarily of servlets. The solution to this problem is JavaServer Pages (JSP)an extension of servlet technology that separates the presentation from the business logic. This lets Java programmers and Web-site designers focus on their strengthswriting Java code and designing Web pages, respectively.

JavaServer Pages simplify the delivery of dynamic Web content. They enable Web application programmers to create dynamic content by reusing predefined components and by interacting with components using server-side scripting. JavaServer Page programmers can use special software components called JavaBeans and custom tag libraries that encapsulate complex, dynamic functionality. A JavaBean is a reusable component that follows certain conventions for class design that are discussed in the JavaBeans specification, which is available at java.sun.com/products/javabeans/glasgow/index.html. Custom-tag libraries are a powerful feature of JSP that allows Java developers to hide complex code for database access and other useful services for dynamic Web pages in custom tags. Web sites use these custom tags like any other Web page element to take advantage of the more complex functionality hidden by the tag. Thus, Web-page designers who are not familiar with Java can enhance Web pages with powerful dynamic content and processing capabilities.

The classes and interfaces that are specific to JavaServer Pages programming are located in packages javax.servlet.jsp and javax.servlet.jsp.tagext. We discuss many of these classes and interfaces throughout this chapter as we present JSP fundamentals. For complete JSP details, see the JavaServer Pages 2.0 specification, which can be downloaded from java.sun.com/products/jsp/download.html. We also include other JSP resources in Section 27.10.