1.1 What Is JavaServer Pages?

Put succinctly, JavaServer 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. As you'll see later in the book, this functionality is key to web applications such as online shopping and employee directories, as well as for personalized and internationalized content.

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, as illustrated in Figure 1-1.

Figure 1-1. Generating dynamic content with JSP elements

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. Programmers 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.