Java  Servlet Programming Exploring Java  Java  Threads Java  Network Programming Java  Virtual Machine Java  AWT Reference Java  Language Reference Java  Fundamental Classes Reference Database Programming with JDBC  and Java  Java  Distributed Computing Developing Java Beans  Java  Security Java  Cryptography Java  Swing Java  Servlet Programming Also from O’Reilly Java  in a Nutshell Java  in a Nutshell, Deluxe Edition Java  Examples in a Nutshell Java  Servlet Programming Jason Hunter with William Crawford Beijing • Cambridge • Farnham • Köln • Paris • Sebastopol • Taipei • Tokyo Java ™ Servlet Programming by Jason Hunter with William Crawford Copyright © 1998 O’Reilly & Associates, Inc. All rights reserved. Printed in the United States of America. Published by O’Reilly & Associates, Inc., 101 Morris Street, Sebastopol, CA 95472. Editor: Paula Ferguson Production Editor: Paula Carroll Editorial and Production Services : Benchmark Productions, Inc. Printing History: October 1998: First Edition Nutshell Handbook, the Nutshell Handbook logo, and the O’Reilly logo are registered trademarks and The Java ™ Series is a trademark of O’Reilly & Associates, Inc. The association of the image of acopper teakettle with the topic of Java ™ Servlet programming is a trademark of O’Reilly & Associates, Inc. Java ™ and all Java-based trademarks and logos are trademarks or registered trademarks of Sun Microsystems, Inc., in the United States and other countries. O’Reilly & Associates, Inc. is independent of Sun Microsystems. Many of the designations used by manufacturers and sellers to distinguish their products are claimed as trademarks. Where those designations appear in this book, and O’Reilly & Associates, Inc. was aware of a trademark claim, the designations have been printed in caps or initial caps. While every precaution has been taken in the preparation of this book, the publisher assumes no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. ISBN: 1-56592-391-X [1/00] [M] v Java™ Servlet Programming, eMatter Edition Copyright © 2000 O’Reilly & Associates, Inc. All rights reserved. opd 0: Table of Contents 0: Preface ix 1. Introduction 1 History of Web Applications 1 Support for Servlets 7 The Power of Servlets 10 2. HTTP Servlet Basics 14 HTTP Basics 14 The Servlet API 17 Page Generation 19 Server-Side Includes 27 Servlet Chaining and Filters 30 JavaServer Pages 37 Moving On 46 3. The Servlet Life Cycle 48 The Servlet Alternative 48 Servlet Reloading 55 Init and Destroy 56 Single-Thread Model 62 Background Processing 64 Last Modified Times 67 vi TABLE OF CONTENTS Java™ Servlet Programming, eMatter Edition Copyright © 2000 O’Reilly & Associates, Inc. All rights reserved. 4. Retrieving Information 70 Initialization Parameters 72 The Server 74 The Client 79 The Request 84 5. Sending HTML Information 124 The Structure of a Response 124 Sending a Normal Response 125 Using Persistent Connections 127 HTML Generation 129 Status Codes 142 HTTP Headers 145 When Things Go Wrong 151 6. Sending Multimedia Content 159 Images 159 Compressed Content 188 Server Push 191 7. Session Tracking 195 User Authorization 196 Hidden Form Fields 197 URL Rewriting 200 Persistent Cookies 202 The Session Tracking API 206 8. Security 221 HTTP Authentication 222 Digital Certificates 232 Secure Sockets Layer (SSL) 234 Running Servlets Securely 237 9. Database Connectivity 242 Relational Databases 243 The JDBC API 246 TABLE OF CONTENTS vii Java™ Servlet Programming, eMatter Edition Copyright © 2000 O’Reilly & Associates, Inc. All rights reserved. Reusing Database Objects 259 Transactions 261 Advanced JDBC Techniques 272 10. Applet-Servlet Communication 277 Communication Options 277 Daytime Server 284 Chat Server 317 11. Interservlet Communication 337 Servlet Manipulation 337 Servlet Reuse 342 Servlet Collaboration 349 Recap 363 12. Internationalization 365 Western European Languages 366 Conforming to Local Customs 369 Non-Western European Languages 371 Multiple Languages 376 Dynamic Language Negotiation 379 HTML Forms 389 Receiving Multilingual Input 395 13. Odds and Ends 397 Parsing Parameters 397 Sending Email 401 Using Regular Expressions 404 Executing Programs 407 Using Native Methods 412 Acting as an RMI Client 413 Debugging 415 Performance Tuning 423 viii TABLE OF CONTENTS Java™ Servlet Programming, eMatter Edition Copyright © 2000 O’Reilly & Associates, Inc. All rights reserved. A. Servlet API Quick Reference 425 B. HTTP Servlet API Quick Reference 447 C. HTTP Status Codes 472 D. Character Entities 478 E. Charsets 484 Index 487 ix Java™ Servlet Programming, eMatter Edition Copyright © 2000 O’Reilly & Associates, Inc. All rights reserved. 0. Preface 0: In late 1996, Java on the server side was coming on strong. Several major software vendors were marketing technologies specifically aimed at helping server-side Java developers do their jobs more efficiently. Most of these products provided a pre built infrastructure that could lift the developer’s attention from the raw socket level into the more productive application level. For example, Netscape intro- duced something it named “server-side applets”; the World Wide Web Consortium included extensible modules called “resources” with its Java-based Jigsaw web server; and with its WebSite server, O’Reilly Software promoted the use of a tech- nology it (only coincidentally) dubbed “servlets.” The drawback: each of these technologies was tied to a particular server and designed for very specific tasks. Then, in early 1997, JavaSoft (a company that has since been reintegrated into Sun Microsystems as the Java Software division) finalized Java servlets. This action consolidated the scattered technologies into a single, standard, generic mecha- nism for developing modular server-side Java code. Servlets were designed to work with both Java-based and non-Java-based servers. Support for servlets has since been implemented in nearly every web server, from Apache to Zeus, and in many non-web servers as well. Servlets have been quick to gain acceptance because, unlike many new technolo- gies that must first explain the problem or task they were created to solve, servlets are a clear solution to a well-recognized and widespread need: generating dynamic web content. From corporations down to individual web programmers, people who struggled with the maintenance and performance problems of CGI-based web programming are turning to servlets for their power, portability, and efficiency. Others, who were perhaps intimidated by CGI programming’s apparent reliance on manual HTTP communication and the Perl and C languages, are looking to servlets as a manageable first step into the world of web programming. x PREFACE Java™ Servlet Programming, eMatter Edition Copyright © 2000 O’Reilly & Associates, Inc. All rights reserved. This book explains everything you need to know about Java servlet programming. The first five chapters cover the basics: what servlets are, what they do, and how they work. The following eight chapters are where the true meat is—they explore the things you are likely to do with servlets. You’ll find numerous examples, several suggestions, a few warnings, and even a couple of true hacks that somehow made it past technical review. We cover Version 2.0 of the Servlet API, which was introduced as part of the Java Web Server 1.1 in December 1997 and clarified by the release of the Java Servlet Development Kit 2.0 in April 1998. Changes in the API from Version 1.0, finalized in June 1997, are noted throughout the text. Audience Is this book for you? It is if you’re interested in extending the functionality of a server—such as extending a web server to generate dynamic content. Specifically, this book was written to help: CGI programmers CGI is a popular but somewhat crude method of extending the functionality of a web server. Servlets provide an elegant, efficient alternative. NSAPI, ISAPI, ASP, and Server-Side JavaScript programmers Each of these technologies can be used as a CGI alternative, but each has limi- tations regarding portability, security, and/or performance. Servlets tend to excel in each of these areas. Java applet programmers It has always been difficult for an applet to talk to a server. Servlets make it easier by giving the applet an easy-to-connect-to, Java-based agent on the server. Authors of web pages with server-side includes Pages that use server-side includes to call CGI programs can use <SERVLET> tags to add content more efficiently to a page. Authors of web pages with different appearances By this we mean pages that must be available in different languages, have to be converted for transmission over a low-bandwidth connection, or need to be modified in some manner before they are sent to the client. Servlets provide something called servlet chaining that can be used for processing of this type. Each servlet in a servlet chain knows how to catch, process, and return a specific kind of content. Thus, servlets can be linked together to do language translation, change large color images to small black-and-white ones, convert images in esoteric formats to standard GIF or JPEG images, or nearly anything else you can think of. [...]... in the javax .servlet. http package to add HTTPspecific functionality The top-level package name is javax instead of the familiar java, to indicate that the Servlet API is a standard extension Every servlet must implement the javax .servlet. Servlet interface Most servlets implement it by extending one of two special classes: javax servlet GenericServlet or javax .servlet. http.HttpServlet A protocol-independent... the server The Servlet API Now that you have a basic understanding of HTTP, we can move on and talk about the Servlet API that you’ll be using to create HTTP servlets, or any kind of servlets, for that matter Servlets use classes and interfaces from two packages: javax servlet and javax .servlet. http The javax .servlet package contains classes to support generic, protocol-independent servlets These classes... server-side JavaScript is available only with Netscape FastTrack Server and Enterprise Server Version 2.0 and above Java Servlet Programming, eMatter Edition Copyright © 2000 O’Reilly & Associates, Inc All rights reserved 6 CHAPTER 1: INTRODUCTION For more information on programming with server-side JavaScript, see http:// developer.netscape.com/tech/javascript/ssjs/ssjs.html Java Servlets Enter Java servlets... unlike applets, they do not require support for Java in the web browser Java Servlet- based Web Server Main Process Request for Servlet1 JVM Thread Servlet1 Request for Servlet2 Request for Servlet1 Thread Thread Servlet2 Figure 1-4 The servlet life cycle Unlike CGI and FastCGI, which use multiple processes to handle separate programs and/or separate requests, servlets are all handled by separate threads... servlet support A plug-in also can be used with a server that provides a poor or outdated servlet implementation Add-on servlet engines include these: • The Java- Apache project’s JServ module, a freely available servlet engine that adds servlet support to the extremely popular Apache server See http:/ /java apache.org/ • Live Software’s JRun, a freely available plug-in designed to support the full Servlet. .. javax .servlet. http.HttpServlet A protocol-independent servlet should subclass GenericServlet, while an HTTP servlet should subclass HttpServlet, which is itself a subclass of GenericServlet with added HTTP-specific functionality Unlike a regular Java program, and just like an applet, a servlet does not have a main() method Instead, certain methods of a servlet are invoked by the server in Java Servlet Programming, eMatter Edition... To keep things as simple as possible, this servlet just says “Hello World” every time it is accessed via a web browser.* Example 2-1 A servlet that prints “Hello World” import java. io.*; import javax .servlet. *; import javax .servlet. http.*; public class HelloWorld extends HttpServlet { public void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException { res.setContentType("text/html");... Java Virtual Machine (JVM), servlet classes need not be bundled with all JVMs More information about the Java Extension Framework is available at http/ /java. sun.com/ products/jdk/1.2/docs/guide/extensions To make it easy for you to develop servlets, Sun has made publicly available a set of classes that provide basic servlet support The javax .servlet and javax servlet. http packages constitute this Servlet. .. portability Servlets are supported on all platforms that support Java, and servlets work with all the major web servers.* Java servlets, as defined by the Java Software division of Sun Microsystems (formerly known as JavaSoft), are the first standard extension to Java This means that servlets are officially blessed by Sun and are part of the Java language, but they are not part of the core Java API Therefore,... lowestcommon-denominator implementation, so you should pick a servlet engine that has the functionality that you want For a complete, up-to-date list of available servlet engines, see the official list maintained by Sun at: http://jserv .java. sun.com/products /java- server/servlets/environments.html The Power of Servlets So far, we have portrayed servlets as an alternative to other dynamic web content technologies, . Java  Servlet Programming Exploring Java  Java  Threads Java  Network Programming Java  Virtual Machine Java  AWT Reference Java  Language. mecha- nism for developing modular server-side Java code. Servlets were designed to work with both Java- based and non -Java- based servers. Support for servlets