Java网络编程第四版精华

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"Java网络编程第四版" 《Java网络编程第四版》是由Elliotte Rusty Harold编写的关于Java网络编程的权威指南。这本书深入探讨了Java在构建网络应用程序时的各种技术和概念，旨在帮助读者掌握利用Java进行网络通信的核心技能。在Java网络编程中，你将学习到以下关键知识点： 1. **基础概念**：了解网络编程的基本原理，包括TCP/IP协议栈、网络套接字（Sockets）以及数据传输的模型。 2. **Java网络API**：详细解析Java提供的网络API，如`java.net`包中的Socket类和ServerSocket类，用于创建客户端和服务器端的连接。同时，还会涉及DatagramSocket和MulticastSocket，用于UDP（用户数据报协议）通信。 3. **HTTP协议**：讲解如何使用Java实现HTTP客户端和服务器，包括GET、POST请求的发送与处理，以及对HTTPS安全协议的支持。 4. **URL和URLConnection**：介绍Java对统一资源定位符（URL）的处理，以及通过URLConnection类进行HTTP和FTP等协议的文件访问。 5. **网络I/O**：讨论NIO（非阻塞I/O）框架，包括Selector、Channel和Buffer，提高网络应用的性能和可扩展性。 6. **异步通信**：讲解Java的异步网络编程模型，如CompletableFuture和ExecutorService，以及Java 9引入的反应式流库。 7. **网络安全**：涵盖加密和身份验证，包括SSL/TLS协议的使用，以及证书管理。 8. **多线程编程**：在处理并发网络连接时，多线程和并发控制策略是至关重要的，书中会详细讲解这部分内容。 9. **错误处理和调试**：介绍如何有效地处理网络编程中的异常和错误，以及调试技巧。 10. **案例研究**：提供实际的示例代码和项目，帮助读者将理论知识应用于实际的网络应用程序开发。此外，本书还涵盖了网络编程的最新发展，如Java 8和Java 9的新特性，以及最新的网络标准和技术。书中的每一章都提供了丰富的练习和实战示例，以帮助读者巩固所学知识，并且每个版本的更新都会根据技术发展进行相应的修订，确保内容的时效性。无论你是初学者还是有经验的开发者，通过阅读《Java网络编程第四版》，你都能系统地学习并提升在网络编程领域的专业技能。

you to start using Java as a platform for serious network programming. To do so, this

book provides a general background in network fundamentals, as well as detailed dis‐

cussions of Java’s facilities for writing network programs. You’ll learn how to write Java

programs that share data across the Internet for games, collaboration, software updates,

file transfer, and more. You’ll also get a behind-the-scenes look at HTTP, SMTP,

TCP/IP, and the other protocols that support the Internet and the Web. When you finish

this book, you’ll have the knowledge and the tools to create the next generation of

software that takes full advantage of the Internet.

About the Fourth Edition

In 1996, in the first edition of this book’s opening chapter, I wrote extensively about the

sort of dynamic, distributed network applications I thought Java would make possible.

One of the most exciting parts of writing subsequent editions has been seeing virtually

all of the applications I foretold come to pass. Programmers are using Java to query

database servers, monitor web pages, control telescopes, manage multiplayer games,

and more, all by using Java’s native ability to access the Internet. Java in general and

network programming in Java in particular has moved well beyond the hype stage and

into the realm of real, working applications.

This book has come a long way, too. The fourth edition focuses even more heavily on

HTTP and REST. HTTP has gone from being one of many network protocols to almost

the network protocol. As you’ll see, it is often the protocol on which other protocols are

built, forming its own layer in the network stack.

There have been lots of other small changes and updates throughout the java.net and

supporting packages in Java 6, 7, and 8, and these are covered here as well. New classes

addressed in this edition include CookieManager, CookiePolicy, CookieStore,

HttpCookie, SwingWorker, Executor, ExecutorService, AsynchronousSocketChan

nel, AsynchronousServerSocketChannel, and more. Many other methods have been

added to existing classes in the last three releases of Java, and these are discussed in the

relevant chapters. I’ve also rewritten large parts of the book to reflect the ever-changing

fashions in Java programming in general and network programming in particular. I

hope you’ll find this fourth edition an even stronger, longer-lived, more accurate, and

more enjoyable tutorial and reference to network programming in Java than the pre‐

vious one.

Organization of the Book

Chapter 1, Basic Network Concepts, explains in detail what a programmer needs to know

about how the networks and the Internet work. It covers the protocols that underlie the

Internet, such as TCP/IP and UDP/IP.

xiv | Preface

The next two chapters throw some light on two parts of Java programming that are

critical to almost all network programs but are often misunderstood and misused: I/O

and threading. Chapter 2, Streams, explores Java’s classic I/O which—despite the new

I/O APIs—isn’t going away any time soon and is still the preferred means of handling

input and output in most client applications. Understanding how Java handles I/O in

the general case is a prerequisite for understanding the special case of how Java handles

network I/O. Chapter 3, Threads, explores multithreading and synchronization, with a

special emphasis on how they can be used for asynchronous I/O and network servers.

Experienced Java programmers may be able to skim or skip these two chapters. However,

Chapter 4, Internet Addresses, is essential reading for everyone. It shows how Java pro‐

grams interact with the Domain Name System through the InetAddress class, the one

class that’s needed by essentially all network programs. Once you’ve finished this chap‐

ter, it’s possible to jump around in the book as your interests and needs dictate.

Chapter 5, URLs and URIs, explores Java’s URL class, a powerful abstraction for down‐

loading information and files from network servers of many kinds. The URL class enables

you to connect to and download files and documents from a network server without

concerning yourself with the details of the protocol the server speaks. It lets you connect

to an FTP server using the same code you use to talk to an HTTP server or to read a file

on the local hard disk. You’ll also learn about the newer URI class, a more standards-

conformant alternative for identifying but not retrieving resources.

Chapter 6, HTTP, delves deeper into the HTTP protocol specifically. Topics covered

include REST, HTTP headers, and cookies. Chapter 7, URLConnections, shows you how

to use the URLConnection and HttpURLConnection classes not just to download data

from web servers, but to upload documents and configure connections.

Chapter 8 through Chapter 10 discuss Java’s low-level socket classes for network access.

Chapter 8, Sockets for Clients, introduces the Java sockets API and the Socket class in

particular. It shows you how to write network clients that interact with TCP servers of

all kinds including whois, dict, and HTTP. Chapter 9, Sockets for Servers, shows you

how to use the ServerSocket class to write servers for these and other protocols. Finally,

Chapter 10, Secure Sockets, shows you how to protect your client-server communica‐

tions using the Secure Sockets Layer (SSL) and the Java Secure Sockets Extension (JSSE).

Chapter 11, Nonblocking I/O, introduces the new I/O APIs specifically designed for

network servers. These APIs enable a program to figure out whether a connection is

ready before it tries to read from or write to the socket. This allows a single thread to

manage many different connections simultaneously, thereby placing much less load on

the virtual machine. The new I/O APIs don’t help much for small servers or clients that

don’t open many simultaneous connections, but they may provide performance boosts

for high-volume servers that want to transmit as much data as the network can handle

as fast as the network can deliver it.

Preface | xv

Chapter 12, UDP, introduces the User Datagram Protocol (UDP) and the associated

DatagramPacket and DatagramSocket classes that provide fast, unreliable communi‐

cation. Finally,

Chapter 13, IP Multicast, shows you how to use UDP to communicate

with multiple hosts at the same time.

Who You Are

This book assumes you are comfortable with the Java language and programming en‐

vironment, in addition to object-oriented programming in general. This book does not

attempt to be a basic language tutorial. You should be thoroughly familiar with the

syntax of Java. You should have written simple applications. It also wouldn’t hurt if you’re

familiar with basic Swing programming, though that’s not required aside from a few

examples. When you encounter a topic that requires a deeper understanding for net‐

work programming than is customary—for instance, threads and streams—I’ll cover

that topic as well, at least briefly.

However, this book doesn’t assume that you have prior experience with network pro‐

gramming. You should find it a complete introduction to networking concepts and

network application development. I don’t assume that you have a few thousand net‐

working acronyms (TCP, UDP, SMTP, etc.) at the tip of your tongue. You’ll learn what

you need to know about these here.

Java Versions

Java’s network classes have changed a lot more slowly since Java 1.0 than other parts of

the core API. In comparison to the AWT or I/O, there have been almost no changes and

only a few additions. Of course, all network programs make extensive use of the I/O

classes and some make heavy use of GUIs. This book is written with the assumption

that you are coding with at least Java 5.0. In general, I use Java 5 features like generics

and the enhanced for loop freely without further explanation.

For network programming purposes, the distinction between Java 5 and Java 6 is not

large. Most examples look identical in the two versions. When a particular method or

class is new in Java 6, 7, or 8, it is noted by a comment following its declaration like this:

public void setFixedLengthStreamingMode(long contentLength) // Java 7

Java 7 is a bit more of a stretch. I have not shied away from using features introduced

in Java 7 where they seemed especially useful or convenient—for instance, try-with-

resources and multicatch are both very helpful when trying to fit examples into the

limited space available in a printed book—but I have been careful to point out my use

of such features.

Overall, though, Java’s networking API has been relatively stable since Java 1.0. Very

little of the post-1.0 networking API has ever been deprecated, and additions have been

xvi | Preface

relatively minor. You shouldn’t have any trouble using this book after Java 8 is released.

New APIs, however, have been somewhat more frequent in the supporting classes, par‐

ticularly I/O, which has undergone three major revisions since Java 1.0.

About the Examples

Most methods and classes described in this book are illustrated with at least one com‐

plete working program, simple though it may be. In my experience, a complete working

program is essential to showing the proper use of a method. Without a program, it is

too easy to drop into jargon or to gloss over points about which the author may be

unclear in his own mind. The Java API documentation itself often suffers from exces‐

sively terse descriptions of the method calls. In this book, I have tried to err on the side

of providing too much explication rather than too little. If a point is obvious to you, feel

free to skip over it. You do not need to type in and run every example in this book; but

if a particular method does give you trouble, you should have at least one working

example.

Each chapter includes at least one (and often several) more complex programs that

demonstrate the classes and methods of that chapter in a more realistic setting. These

often rely on Java features not discussed in this book. Indeed, in many of the programs,

the networking components are only a small fraction of the source code and often the

least difficult parts. Nonetheless, none of these programs could be written as easily in

languages that didn’t give networking the central position it occupies in Java. The ap‐

parent simplicity of the networked sections of the code reflects the extent to which

networking has been made a core feature of Java, and not any triviality of the program

itself. All example programs presented in this book are available online, often with

corrections and additions. You can download the source code from

http://www.cafeau

lait.org/books/jnp4/.

I have tested all the examples on Linux and many on Windows and Mac OS X. Most of

the examples given here should work on other platforms and with other compilers and

virtual machines that support Java 5 or later. The most common reasons an example

may not compile with Java 5 or 6 are try-with-resources and multicatch. These examples

can easily be rewritten to support earlier Java versions at the cost of increased verbosity.

I do feel a little guilty about a couple of compromises necessitated by the needs of space

in a printed book. First, I rarely check preconditions. Most methods assume they are

passed good data, and dispense with null checks and similar principles of good code

hygiene. Furthermore, I have reduced the indentation to two characters per block and

four characters per continuation line, as opposed to the Java standard of four and eight,

respectively. I hope these flaws will not be too distracting. On the positive side, these

compromises have aided me in making this edition considerably shorter (by several

hundred pages) than the previous edition.

Preface | xvii

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