深入探索Java Servlet编程

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"O'Reilly 出版的 Java Servlet Programming 是一本深入探讨 Java 服务器端编程技术的专业书籍，由 Jason Hunter 和 William Crawford 合著。该书涵盖了与 Java Servlet 相关的各种主题，旨在帮助读者理解和掌握如何使用 Java 技术进行 Web 应用程序开发。" 在这本书中，读者可以学习到以下关键知识点： 1. **Java Servlet**：Servlet 是 Java 平台上用于构建动态 Web 应用的核心技术，它扩展了 Web 服务器的功能，使得开发者可以用 Java 编程语言来处理 HTTP 请求。书中会详细介绍 Servlet 的生命周期、服务方法、初始化参数以及如何部署和配置 Servlet。 2. **HTTP 协议理解**：为了有效地使用 Servlet，开发者需要理解 HTTP 协议的基本原理，包括请求方法（GET、POST等）、状态码、头部信息以及请求体和响应体的处理。 3. **Web 应用程序架构**：书中可能涵盖了 Web 应用的目录结构、部署描述符（web.xml）的编写，以及如何组织和管理应用程序的组件。 4. **JSP（JavaServer Pages）**：作为与 Servlet 配合使用的视图层技术，JSP 可以方便地创建动态网页。读者将学习 JSP 基本语法、EL（Expression Language）和 JSTL（JavaServer Pages Standard Tag Library）的使用。 5. **JDBC（Java Database Connectivity）**：通过 JDBC，Java 应用可以与各种数据库交互。书中可能会讲解如何连接数据库、执行 SQL 查询、处理结果集以及事务管理。 6. **MVC（Model-View-Controller）模式**：Servlet 通常结合 MVC 设计模式来构建 Web 应用，书中可能涉及如何实现这种模式以及其在 Web 开发中的优势。 7. **Java 容器和容器管理的组件**：如 Tomcat、Jetty 等，这些容器负责加载、管理和运行 Servlet。读者会了解如何配置和调试这些容器，以优化应用程序性能。 8. **安全性**：Java Servlet 在 Web 应用中的安全问题，包括认证、授权、会话管理、防止 SQL 注入和跨站脚本攻击等。 9. **性能优化**：如何使用缓存、减少数据库访问、异步处理和线程管理来提高应用程序的性能。 10. **错误处理和日志记录**：在开发过程中，正确处理异常和记录日志是至关重要的。书中可能讲解如何实现有效的错误处理策略和日志记录机制。此外，O'Reilly 出版社还出版了一系列关于 Java 的其他书籍，如《Java in a Nutshell》、《Java Distributed Computing》和《Java Security》，这些资源可作为扩展阅读，帮助读者全面掌握 Java 技术栈。《Java Servlet Programming》是一本深入而全面的指南，适合希望深入了解 Java Web 开发的程序员阅读。通过这本书，读者不仅可以学习到 Servlet 的核心概念和技术，还能了解到与之相关的网络编程、数据库交互、应用架构设计等多个领域的知识。

xvi PREFACE

Java™ Servlet Programming, eMatter Edition

(who looks the spitting image of James Gosling), Jim Driscoll, Rob Clark, and Dave

Brownell.

Thanks also to the members of the jserv-interest mailing list, whose questions and

answers have shaped the content of this book; Will Ramey, an old friend who

didn’t let friendship blind his critical eye; Mike Engber, the man to whom I turned

when I had run out of elegant workarounds and was ready to accept the crazy

things he comes up with; Dave Vandegrift, the first person to read many of the

chapters; Bill Day, author of Java Media Players, who helped intangibly by going

through the book writing process in parallel with me; Michael O’Connell and Jill

Steinberg, editors at JavaWorld, where I did my first professional writing; Doug

Young, who shared with me the tricks he learned writing seven technical books of

his own; and Shoji Kuwabara, Mieko Aono, Song Yung, Matthew Kim, and Alex-

andr Pashintsev for their help translating “Hello World” for Chapter 12.

Finally, thanks to Mom and Dad, for their love and support and for the time they

spent long ago teaching me the basics of writing. And a special thanks to my girl-

friend, Kristi Taylor, who made the small time away from work a pleasure.

And Grandpa, I wish you could have seen this.

Jason Hunter

July 1998

William Crawford

First and foremost, thanks to Shelley Norton, Dr. Isaac Kohane, Dr. James Fackler,

and Dr. Richard Kitz (plus a supporting cast whose contributions were invalu-

able), whose assistance and early support have made everything since possible.

Also, to Martin Streeter of Invantage, Inc., for his support during this project.

Without Rob Leith, Roger Stacey, and Fred Strebeigh, I would probably still be

stuck in the passive voice. Dale Dougherty offered me money in exchange for

words, a twist of events that I still haven’t gotten over. Andy Kwak, Joel Pomerantz,

and Matthew Proto, brave souls all, were willing to read drafts and listen to

complaints at one o’clock in the morning.

And, of course, to Mom and Dad for their years of support, and to my sister Faith

for (usually) letting me get away with being a nerd.

William Crawford

July 1998

Java™ Servlet Programming, eMatter Edition

Chapter 1

In this chapter:

• History of Web

Applications

• Support for Servlets

• The Power of Servlets

1. Introduction 1:

The rise of server-side Java applications is one of the latest and most exciting

trends in Java programming. The Java language was originally intended for use in

small, embedded devices. It was first hyped as a language for developing elaborate

client-side web content in the form of applets. Until recently, Java’s potential as a

server-side development platform had been sadly overlooked. Now, Java is coming

into its own as a language ideally suited for server-side development.

Businesses in particular have been quick to recognize Java’s potential on the

server—Java is inherently suited for large client/server applications. The cross-

platform nature of Java is extremely useful for organizations that have a heteroge-

neous collection of servers running various flavors of the Unix and Windows

operating systems. Java’s modern, object-oriented, memory-protected design

allows developers to cut development cycles and increase reliability. In addition,

Java’s built-in support for networking and enterprise APIs provides access to legacy

data, easing the transition from older client/server systems.

Java servlets are a key component of server-side Java development. A servlet is a

small, pluggable extension to a server that enhances the server’s functionality.

Servlets allow developers to extend and customize any Java-enabled server—a web

server, a mail server, an application server, or any custom server—with a hitherto

unknown degree of portability, flexibility, and ease. But before we go into any

more detail, let’s put things into perspective.

History of Web Applications

While servlets can be used to extend the functionality of any Java-enabled server,

today they are most often used to extend web servers, providing a powerful, effi-

cient replacement for CGI scripts. When you use a servlet to create dynamic

2CHAPTER 1: INTRODUCTION

Java™ Servlet Programming, eMatter Edition

content for a web page or otherwise extend the functionality of a web server, you

are in effect creating a web application. While a web page merely displays static

content and lets the user navigate through that content, a web application

provides a more interactive experience. A web application can be as simple as a

keyword search on a document archive or as complex as an electronic storefront.

Web applications are being deployed on the Internet and on corporate intranets

and extranets, where they have the potential to increase productivity and change

the way that companies, large and small, do business.

To understand the power of servlets, we need to step back and look at some of the

other approaches that can be used to create web applications.

Common Gateway Interface

The Common Gateway Interface, normally referred to as CGI, was one of the first

practical techniques for creating dynamic content. With CGI, a web server passes

certain requests to an external program. The output of this program is then sent

to the client in place of a static file. The advent of CGI made it possible to imple-

ment all sorts of new functionality in web pages, and CGI quickly became a de

facto standard, implemented on dozens of web servers.

It’s interesting to note that the ability of CGI programs to create dynamic web

pages is a side effect of its intended purpose: to define a standard method for an

information server to talk with external applications. This origin explains why CGI

has perhaps the worst life cycle imaginable. When a server receives a request that

accesses a CGI program, it must create a new process to run the CGI program and

then pass to it, via environment variables and standard input, every bit of informa-

tion that might be necessary to generate a response. Creating a process for every

such request requires time and significant server resources, which limits the

number of requests a server can handle concurrently. Figure 1-1 shows the CGI

life cycle.

Figure 1-1. The CGI life cycle

CGI-based Web Server

Main Process

Request for CGI1

Request for CGI2

Request for CGI1

Child Process for CGI1

Child Process for CGI2

Child Process for CGI1

HISTORY OF WEB APPLICATIONS 3

Java™ Servlet Programming, eMatter Edition

Even though a CGI program can be written in almost any language, the Perl

programming language has become the predominant choice. Its advanced text-

processing capabilities are a big help in managing the details of the CGI interface.

Writing a CGI script in Perl gives it a semblance of platform independence, but it

also requires that each request start a separate Perl interpreter, which takes even

more time and requires extra resources.

Another often-overlooked problem with CGI is that a CGI program cannot

interact with the web server or take advantage of the server’s abilities once it

begins execution because it is running in a separate process. For example, a CGI

script cannot write to the server’s log file.

For more information on CGI programming, see CGI Programming on the World

Wide Web by Shishir Gundavaram (O’Reilly).

FastCGI

A company named Open Market developed an alternative to standard CGI named

FastCGI. In many ways, FastCGI works just like CGI—the important difference is

that FastCGI creates a single persistent process for each FastCGI program, as

shown in Figure 1-2. This eliminates the need to create a new process for each

request.

Although FastCGI is a step in the right direction, it still has a problem with process

proliferation: there is at least one process for each FastCGI program. If a FastCGI

program is to handle concurrent requests, it needs a pool of processes, one per

request. Considering that each process may be executing a Perl interpreter, this

approach does not scale as well as you might hope. (Although, to its credit, FastCGI

can distribute its processes across multiple servers.) Another problem with FastCGI

is that it does nothing to help the FastCGI program more closely interact with the

server. As of this writing, the FastCGI approach has not been implemented by some

Figure 1-2. The FastCGI life cycle

Main Process

Request for CGI1

Request for CGI2

Request for CGI1

Single Child Process for CGI1

Single Child Process for CGI2

FastCGI-based Web Server

4CHAPTER 1: INTRODUCTION

Java™ Servlet Programming, eMatter Edition

of the more popular servers, including Microsoft’s Internet Information Server.

Finally, FastCGI programs are only as portable as the language in which they’re

written.

For more information on FastCGI, see http://www.fastcgi.com/.

mod_perl

If you are using the Apache web server, another option for improving CGI perfor-

mance is using mod_perl. mod_perl is a module for the Apache server that embeds a

copy of the Perl interpreter into the Apache httpd executable, providing complete

access to Perl functionality within Apache. The effect is that your CGI scripts are

precompiled by the server and executed without forking, thus running much

more quickly and efficiently. For more information on mod_perl, see http://perl.

apache.org/.

PerlEx

PerlEx, developed by ActiveState, improves the performance of CGI scripts written

in Perl that run on Windows NT web servers (Microsoft’s Internet Information

Server, O’Reilly’s WebSite Professional, and Netscape’s FastTrack Server and

Enterprise Server). PerlEx uses the web server’s native API to achieve its perfor-

mance gains. For more information, see http://www.activestate.com/plex/.

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