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Introducing Java Server PagesHome > Build > Backend > Java Server Pages CHAPTER
7- Introducing Java Server Pages So what are JavaServer Pages? Well, they combine markup (whether HTML or XML) with nuggets of Java code to produce a dynamic web page. Each page is automatically compiled to a servlet by the JSP engine, the first time it is requested, and then executed. JSP provides a variety of ways to talk to Java classes, servlets, applets and the web server. With it, you can split the functionality of your web applications into components with well-defined public interfaces glued together by a simple page. This model allows tasks to be subdivided - a developer builds custom components and the page designer assembles the application with a few judicious method calls. In this 'application assembly' model, the business logic is separated from the presentation of data. To give you an idea of the future, this separation of logic and presentation may become yet more extreme with the use of custom tags slated for JSP 1.1. JavaServer Pages is a specification that is already implemented by several web servers (for more details, see the JSP FAQ at http://www.esperanto.org.nz/jsp/jspfaq.html), on which your code will run without change, making it more portable and the server market more competitive than its rivals. Finally, it's nice and simple! In this chapter, we will: Ø
Discuss the JavaServer Pages (JSP) architecture Ø
Look at the elements of a JSP file, and the
tags used to represent them Ø
Encapsulate logic in a JavaBean component
and integrate it with JSP Ø
Walk through a detailed example using JSP,
showing a typical web application architecture Architectural
Overview
A JavaServer Page is a simple text file consisting of HTML or XML content along with JSP elements (a sort of shorthand for Java code). When a client requests a JSP page of the web server and it has not been run before, the page is first passed to a JSP engine which compiles the page to a servlet, runs it and returns the resulting content to the client. Thereafter, the web server's servlet engine will run the compiled page. It should be no surprise, given the flexibility of the servlet model, that the current reference implementation of the JSP engine is itself a servlet. It is possible to view the finished servlet code that is generated by locating it within the directory structure of the servlet engine. For example, with JRun, you can find the source code for your JSP files (in servlet form) in the jrun/jsm-default/services/jse/servlets/jsp directory. This is very helpful when trying to debug your JSP files. If you take a look in the source files for the javax.servlet.jsp package, you'll find the following classes: Ø
JSPPage Ø
HttpJspPage Ø
jspDestroy() Ø
_jspService(HttpServletRequest
request, HttpServletResponse response)  |
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