JavaServer Pages, 2nd Edition
From Publisher:
Since its inception in 1999, Enterprise Java has taken the Java programming community by storm--developers have realized its potential for building distributed applications. Today, JavaServer Pages (JSP) continues to harmonize how web designers and programmers create dynamic
web sites. JSP builds on the popular Java servlet technology and makes it easier to develop dynamic web applications--even if you're not a hard-core programmer.
JavaServer Pages, 2nd Edition is completely revised and updated to cover the substantial changes in the 1.2 version of the JSP specification, and also includes detailed coverage of the new JSP Standard Tag Library (JSTL)--an eagerly anticipated specification of a set of JSP elements for the tasks needed in most JSP applications. This book starts off by illustrating how JSP capitalizes on the power of Java servlets to create effective, portable web applications. It shows how to get started using the Apache Tomcat server, and provides detailed coverage of JSP syntax and features, error handling and debugging, authentication and personalization, and how to use JSTL for database access, XML processing, and internationalization.
JavaServer Pages recognizes the different needs of the two groups of professionals who want to learn JSP: page authors interested in using JSP elements in web pages, and programmers concerned with learning the JSP API and using JSP effectively in an enterprise application. If you're in the latter group, this book also teaches you such advanced topics as integrating servlets and JavaBeans with JSP, using the popular Apache Struts MVC framework to illustrate how it's done. Finally, the author presents how to develop custom tag libraries, using realistic examples that you can use as a springboard for your own JSP libraries.
Chapter 3
JSP Overview
JSP is the latest Java technology for web application development and is based on the servlet technology introduced in the previous chapter. While servlets are great in many ways, they are generally reserved for programmers. In this chapter, we look at the problems that JSP technology solves, the anatomy of a JSP page, the relationship between servlets and JSP, and how the server processes a JSP page.
In any web application, a program on the server processes requests and generates responses. In a simple one-page application, such as an online bulletin board, you don't need to be overly concerned about the design of this piece of code; all logic can be lumped together in a single program. However, when the application grows into something bigger (spanning multiple pages, using external resources such as databases, with more options and support for more types of clients), it's a different story. The way your site is designed is critical to how well it can be adapted to new requirements and continue to evolve. The good news is that JSP technology can be used as an important part in all kinds of web applications, from the simplest to the most complex. Therefore, this chapter also introduces the primary concepts in the design model recommended for web applications and the different roles played by JSP and other Java technologies in this model.
The Problem with Servlets
In many Java servlet-based applications, processing the request and generating the response are both handled by a single servlet class. Example 3-1 shows how a servlet class often looks.
Example 3-1:
A typical servlet class
public class OrderServlet extends HttpServlet {
public void doGet((HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html");
PrintWriter out = response.getWriter( );
if (isOrderInfoValid(request)) {
saveOrderInfo(request);
out.println("<html>");
out.println(" <head>");
out.println(" <title>Order Confirmation</title>");
out.println(" </head>");
out.println(" <body>");
out.println(" <h1>Order Confirmation</h2>");
renderOrderInfo(request);
out.println(" </body>");
out.println("</html>");
}
...
If you're not a programmer, don't worry about all the details in this code. The point is that the servlet contains request processing and business logic (implemented by methods such as isOrderInfoValid( ) and saveOrderInfo( )), and also generates the response HTML code, embedded directly in the servlet code using println( ) calls. A more structured servlet application isolates different pieces of the processing in various reusable utility classes and may also use a separate class library for generating the actual HTML elements in the response. Even so, the pure servlet-based approach still has a few problems:
- Thorough Java programming knowledge is needed to develop and maintain all aspects of the application, since the processing code and the HTML elements are lumped together.
- Changing the look and feel of the application, or adding support for a new type of client (such as a WML client), requires the servlet code to be updated and recompiled.
- It's hard to take advantage of web-page development tools when designing the application interface. If such tools are used to develop the web page layout, the generated HTML must then be manually embedded into the servlet code, a process which is time consuming, error prone, and extremely boring.
Adding JSP to the puzzle lets you solve these problems by separating the request processing and business logic code from the presentation, as illustrated in Figure 3-1. Instead of embedding HTML in the code, you place all static HTML in a JSP page, just as in a regular web page, and add a few JSP elements to generate the dynamic parts of the page. The request processing can remain the domain of the servlet, and the business logic can be handled by JavaBeans and EJB components.
Figure 3-1.
Separation of request processing, business logic, and presentation
|
|
As I mentioned before, separating the request processing and business logic from presentation makes it possible to divide the development tasks among people with different skills. Java programmers implement the request processing and business logic pieces, web page authors implement the user interface, and both groups can use best-of-breed development tools for the task at hand. The result is a much more productive development process. It also makes it possible to change different aspects of the application independently, such as changing the business rules without touching the user interface.
This model has clear benefits even for a web-page author without programming skills, working alone. A page author can develop web applications with many dynamic features, using the JSP standard actions and the JSTL libraries, as well as Java components provided by open source projects and commercial companies.
New on the Java Boutique:
New Review:
Time Management Made Easy with the Quartz Enterprise Job Scheduler
Why not just use the Java timer API? This open source scheduling
API boasts simplicity, ease-of-integration, a well-rounded feature
set, and it's free!
New Applet:
Reverse Complement
Reverse Complement is a simple applet that converts DNA or RNA
sequences into three useful formats.
Elsewhere on internet.com:
WebDeveloper Java
Lots of Java information on webdeveloper.com
WDVL Java
Thorough Java resource at the Web Developer's Virtual Library.
ScriptSearch Java
Hundreds of free Java code files to download.
jGuru: Your View of the Java Universe
Customizable portal with online training, FAQs, regular news updates, and tutorials.
|
