JavaServer Pages, 3rd Edition

Using JSP Action Elements

Besides the fixed template text, the easy.jsp page also produces dynamic content. It has very simple dynamic content—the sum of 1, 2 and 3 calculated at runtime—but step back a moment and think about the type of dynamic content you see on the Web every day. Common examples might be a list of web sites matching a search criterion on a search engine site, the content of a shopping cart on an e-commerce site, a personalized news page, or messages in a bulletin board. The actual data for the dynamic content can come from many types of sources, for instance from a database, an XML document, or data accumulated in memory based on previous requests. The dynamic data needs to be combined with regular HTML elements into a page with the right layout, navigation bars, the company logo, and so forth, before it’s sent to the browser. When using JSP, the regular HTML is the template text described earlier, and the dynamic data is inserted at the appropriate place in the template text using a JSP action element.

A JSP action is executed when a JSP page is requested (this is called the request processing phase, as you may recall from Chapter 3). In other words, JSP action elements represent dynamic actions that take place at runtime, as opposed to JSP directives that are used only during the translation phase (when the JSP page is turned into Java servlet code). An action can add text to the response, as in the example used in this chapter, but it can also do other things ...