Introduction
Suppose your company wants to sell products online. You have a database that gives the price and inventory status of each item. But, your database doesn’t speak HTTP, the protocol that Web browsers use. Nor does it output HTML, the format Web browsers need. What can you do? Once users know what they want to buy, how do you gather that information? You want to customize your site based on visitors’ preferences and interests—how? You want to let users see their previous purchases, but you don’t want to reveal that information to other visitors. How do you enforce these security restrictions? When your Web site becomes popular, you might want to compress pages to reduce bandwidth. How can you do this without causing your site to fail for the 30% of visitors whose browsers don’t support compression? In all these cases, you need a program to act as the intermediary between the browser and some server-side resource. This book is about using the Java platform for this type of program.
“Wait a second,” you say. “Didn’t you already write a book about that?” Well, yes. In May of 2000, Sun Microsystems Press and Prentice Hall released my second book, Core Servlets and JavaServer Pages. It was successful beyond everyone’s wildest expectations, selling approximately 100,000 copies in the first year, getting translated into Bulgarian, Chinese, Czech, French, German, Hebrew, Japanese, Korean, Polish, Russian, and Spanish, and being chosen by Amazon.com as one of the top five computer programming books of 2001. Even better, I was swamped with requests for what I really like doing: teaching short courses for developers in industry. Despite having to decline most of the requests, I was still able to teach servlet and JSP short courses in Australia, Canada, Japan, the Philippines, and at a variety of U.S. venues. What fun!
Since then, use of servlets and JSP has continued to grow at a phenomenal rate. The Java 2 Platform has become the technology of choice for developing e-commerce applications, dynamic Web sites, and Web-enabled applications and service. Servlets and JSP continue to be the foundation of this platform—they provide the link between Web clients and server-side applications. Virtually all major Web servers for Windows, Unix (including Linux), MacOS, VMS, and mainframe operating systems now support servlet and JSP technology either natively or by means of a plugin. With only a small amount of configuration, you can run servlets and JSP in Microsoft IIS, iPlanet/Netscape Enterprise Server, the Apache Web Server, IBM WebSphere, BEA WebLogic, and dozens of other servers. Performance of both commercial and open-source servlet and JSP engines has improved significantly.
However, the field continues to evolve rapidly. For example:
The official servlet and JSP reference implementation is no longer developed by Sun. Instead, it is Apache Tomcat, an open-source product developed by a team from many different organizations.
Use of Web applications to bundle groups of servlets and JSP pages has grown significantly.
Portable mechanisms for enforcing Web application security have started to displace the server-specific mechanisms that were formerly used.
Version 2.3 of the servlet specification was released (August 2001). New features in this specification include servlet and JSP filters, application life-cycle event handlers, and a number of smaller additions and changes to existing APIs and to the deployment descriptor (web.xml).
Version 1.2 of the JSP specification was released (also August 2001). This version lets you bundle event listeners with tag libraries, lets you designate XML-based programs to check the syntax of pages that use custom tags, and supplies interfaces that let your custom tags loop more efficiently and handle errors more easily. JSP 1.2 also makes a number of smaller changes and additions to existing APIs and to the TLD file format.
XML has become firmly entrenched as a data-interchange language. Servlet and JSP pages use it for configuration files. Tag library validators can use it to verify custom tag syntax. JSP pages can be represented entirely in XML.
Throughout 2000 and 2001, the JSR-052 expert group put together a standard tag library for JSP. In November of 2001 they released early access version 1.2 of this library, called JSTL (JSP Standard Tag Library). This library provides standard tags for simple looping, iterating over a variety of data structures, evaluating content conditionally, and accessing objects without using explicit scripting code.
Whew. Lots of changes. The new features are very useful, but is there a single place where you can learn about all of them? Here! That’s why I wrote this book: to show developers how to make use of all of these new features. If you aren’t familiar with basic servlet and JSP development, don’t worry. I provide a thorough review at the beginning of the book.