O'Reilly - Java Network Programming (2nd edition) (2000).pdf - Java - Witek63

Preface

Java™'s growth over the last five years has been nothing short of phenomenal. Given

Java's rapid rise to prominence and the general interest in networking, it's a little

surprising that network programming in Java is still so mysterious to so many. This

doesn't have to be. In fact, writing network programs in Java is quite simple, as this

book will show. Readers with previous experience in network programming in a Unix,

Windows, or Macintosh environment should be pleasantly surprised at how much

easier it is to write equivalent programs in Java. That's because the Java core API

includes well-designed interfaces to most network features. Indeed, there is very little

application layer network software you can write in C or C++ that you can't write

more easily in Java. Java Network Programming endeavors to show you how to take

advantage of Java's network class library to quickly and easily write programs that

accomplish many common networking tasks. These include:

• Browsing pages on the Web

• Parsing and rendering HTML

• Sending email with SMTP

• Receiving email with POP and IMAP

• Writing multithreaded servers

• Installing new protocol and content handlers into browsers

• Encrypting communications for confidentiality, authentication, and guaranteed

message integrity

• Designing GUI clients for network services

• Posting data to CGI programs

• Looking up hosts using DNS

• Downloading files with anonymous FTP

• Connecting sockets for low-level network communication

• Distributing applications across multiple systems with Remote Method

Invocation

Java is the first language to provide such a powerful cross-platform network library

that handles all these diverse tasks. Java Network Programming exposes the power

and sophistication of this library. This book's goal is to enable 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 discussions of Java's

facilities for writing network programs. You'll learn how to write Java applets and

applications 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, CGI,

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 Second Edition

In the first chapter of the first edition of this book, 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 this second edition was seeing that virtually

all of the applications I had postulated have indeed 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 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. Not all network software

is written in Java yet, but it's not for a lack of trying. Efforts are well under way to

subvert the existing infrastructure of C-based network clients and servers with pure

Java replacements. It's unlikely that Java will replace C for all network programming

in the near future. However, the mere fact that many people are willing to use web

browsers, web servers, and more written in Java shows just how far we've come since

1996.

This book has come a long way too. The second edition has been rewritten almost

from scratch. There are five completely new chapters, some of which reflect new

APIs and abilities of Java introduced since the first edition was published ( Chapter 8 ,

Chapter 12 , and Chapter 19 ), and some of which reflect my greater experience in

teaching this material and noticing exactly where students' trouble spots are ( Chapter

4 , and Chapter 5 ). In addition, one chapter on the Java Servlet API has been removed,

since the topic really deserves a book of its own; and indeed Jason Hunter has written

that book, Java Servlet Programming (O'Reilly & Associates, Inc., 1998).

However, much more important than the added and deleted chapters are the changes

inside the chapters that we kept. The most obvious change to the first edition is that all

of the examples have been rewritten with the Java 1.1 I/O API. The deprecation

messages that tormented readers who compiled the first edition's examples using Java

1.1 or later are now a thing of the past. Less obviously, but far more importantly, all

the examples have been rewritten from the ground up to use clean, object-oriented

design that follows Java's naming conventions and design principles. Like almost

everyone (Sun not excepted), I was still struggling to figure out a lot of the details of

just what one did with Java and how one did it when I wrote the first edition in 1996.

The old examples got the network code correct, but in most other respects they now

look embarrassingly amateurish. I've learned a lot about both Java and object-oriented

programming since then, and I think my increased experience shows in this edition.

For just one example, I no longer use standalone applets where a simple frame-based

application would suffice. I hope that the new examples will serve as models not just

of how to write network programs, but also of how to write Java code in general.

And of course the text has been cleaned up too. In fact, I took as long to write this

second, revised edition as I did to write the original edition. As previously mentioned,

there are 5 completely new chapters, but the 14 revised chapters have been

extensively rewritten and expanded to bring them up-to-date with new developments,

as well as to make them clearer and more engaging. This edition is, to put it frankly, a

much better written book than the first edition, even leaving aside all the changes to

the examples. I hope you'll find this edition an even stronger, longer lived, more

accurate, and more enjoyable tutorial and reference to network programming in Java

than the first edition.

Organization of the Book

This book begins with three chapters that outline how networks and network

programs work. Chapter 1 , is a gentle introduction to network programming in Java

and the applications that it makes possible. All readers should find something of

interest in this chapter. It explores some of the unique programs that become feasible

when networking is combined with Java. Chapter 2 , and Chapter 3 , explain in detail

what a programmer needs to know about how the Internet and the Web work. Chapter

2 describes the protocols that underlie the Internet, such as TCP/IP and UDP/IP.

Chapter 3 describes the standards that underlie the Web such, as HTTP, HTML, and

CGI. If you've done a lot of network programming in other languages on other

platforms, you may be able to skip these two chapters.

The next two chapters throw some light on two parts of Java that are critical to almost

all network programs but are often misunderstood and misused: I/O and threading.

Chapter 4 explores Java's unique way of handling input and output. 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 5 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 6 , is essential reading for everyone. It shows

how Java programs 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 chapter, it's possible to jump around in the book as your interests and

needs dictate. There are, however, some interdependencies between specific chapters.

Figure P.1 should allow you to map out possible paths through the book.

Figure P.1. Chapter prerequisites

Chapter 7 , explores Java's URL class, a powerful abstraction for downloading

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 that 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.

Once you've retrieved an HTML file from a server, you're going to want to do

something with it. Parsing and rendering HTML is one of the most difficult

challenges network programmers face. Indeed, the Mozilla project has been struggling

with that exact problem for more than two years. Chapter 8 , introduces some little-

known classes for parsing and rendering HTML documents that take this burden off

your shoulders and put it on Sun's.

Chapter 9 , investigates the network methods of one the first classes every Java

programmer learns about, Applet . You'll see how to load images and audio files from

network servers and track their progress. Without using undocumented classes, this is

the only way to handle audio in Java 1.2 and earlier.

Chapter 10 through Chapter 14 discuss Java's low-level socket classes for network

access. Chapter 10 , 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, finger, and HTTP. Chapter 11 , shows you how to use the

ServerSocket class to write servers for these and other protocols in Java. Chapter 12 ,

shows you how to protect your client/server communications using the Secure Sockets

Layer (SSL) and the Java Secure Sockets Extension ( JSSE). Chapter 13 , introduces

the User Datagram Protocol (UDP) and the associated classes DatagramPacket and

DatagramSocket for fast, reliable communication. Finally, Chapter 14 , shows you

how to use UDP to communicate with multiple hosts at the same time. All the other

classes that access the network from Java rely on the classes described in these five

chapters.

Chapter 15 through Chapter 17 look more deeply at the infrastructure supporting the

URL class. These chapters introduce protocol and content handlers, concepts unique to

Java that make it possible to write dynamically-extensible software that automatically

understands new protocols and media types. Chapter 15 , describes the

URLConnection class that serves as the engine for the URL class of Chapter 7 . It shows

you how to take advantage of this class through its public API. Chapter 16 , also

focuses on the URLConnection class but from a different direction; it shows you how

to subclass this class to create handlers for new protocols and URLs. Finally, Chapter

17 explores Java's somewhat moribund mechanism for supporting new media types.

Chapter 18 and Chapter 19 introduce two unique higher-level APIs for network

programs, Remote Method Invocation (RMI) and the JavaMail API. Chapter 18 ,

introduces this powerful mechanism for writing distributed Java applications that run

across multiple heterogeneous systems at the same time while communicating with

straightforward method calls just like a nondistributed program. Chapter 19 , acquaints

you with this standard extension to Java that offers an alternative to low-level sockets

for talking to SMTP, POP, IMAP, and other email servers. Both of these APIs provide

distributed applications with less cumbersome alternatives to lower-level protocols.

Who You Are

This book assumes you have a basic familiarity with the Java language and

programming environment, 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 the language. You should have written simple applications

and applets. You should also be comfortable with the AWT. When you encounter a

topic that requires a deeper understanding for network programming than is

customary—for instance, threads and streams—I'll cover that topic as well, at least

briefly.

You should also be an accomplished user of the Internet. I will assume you know how

to ftp files and visit web sites. You should know what a URL is and how you locate

one. You should know how to write simple HTML and be able to publish a home

page that includes Java applets, though you do not need to be a super web designer.

However, this book doesn't assume that you have prior experience with network

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

network application development. I don't assume that you have a few thousand

networking acronyms (TCP, UDP, SMTP . . .) at the tip of your tongue. You'll learn

what you need to know about these here. It's certainly possible that you could use this

book as a general introduction to network programming with a socket-like interface,

then go on to learn the Windows Socket Architecture (WSA), and figure out how to

write network applications in C++. But it's not clear why you would want to: Java lets

you write very sophisticated applications with ease.

O'Reilly - Java Network Programming (2nd edition) (2000).pdf

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