Java I/O 2nd Edition：深入理解输入输出系统

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"Java IO 2nd Edition PDF" Java IO 第二版是一本深入探讨Java输入/输出（I/O）机制的专业书籍，由Elliotte Rusty Harold撰写，并由O'Reilly出版社于2006年5月出版。这本书涵盖了726页的内容，包括完整的目录和索引，旨在帮助读者理解和掌握Java I/O系统的各个方面。 Java的I/O设施基于流，流提供了一种简单的方式，用于读取和写入不同类型的数据显示，Java提供了多种不同类型的流，每种都有其特定的应用场景。流的宇宙可以大致分为四个主要类别：输入流和输出流，用于处理二进制数据；以及读者和作家，用于处理文本（字符）数据。基础的流类型可能对大多数开发者来说并不陌生，但书中还介绍了如CipherInputStream用于读取加密数据，以及ZipOutputStream用于自动压缩数据等更高级的流类型。了解如何有效地使用缓冲流以提高I/O操作效率也是本书的重要内容。在讨论I/O时，字符集和格式化是不可或缺的主题。Java支持Unicode字符集，使得处理多语言和国际化文本成为可能。书中详细解释了如何在Java中处理不同的字符编码，以及如何进行文本的格式化输出，包括日期、时间和其他数值的格式化。此外，Java的I/O系统还包括文件和文件系统操作，如创建、删除、重命名文件，以及目录管理。书中还会涉及NIO（New IO）框架，这是Java 1.4引入的一个增强型I/O接口，提供了非阻塞I/O和通道的概念，这对于高性能网络编程和大容量数据处理尤其重要。NIO还包括选择器（Selector），它允许一个线程管理多个I/O通道，提高了并发处理的能力。网络I/O也是Java I/O中的重要部分，包括套接字（Socket）编程，服务器套接字（ServerSocket）以及HTTP、FTP等协议的实现。书中将详细介绍如何使用这些工具进行客户端和服务器之间的通信。错误处理和异常处理在任何编程中都是关键，Java IO也不例外。读者将学习如何妥善处理I/O相关的异常，确保程序的健壮性。同时，书中还会探讨性能优化策略，包括使用缓冲、异步I/O以及最佳实践，帮助开发者写出高效且可靠的I/O代码。 Java IO 2nd Edition是全面理解Java I/O系统的一本权威指南，它不仅适合初学者入门，也为有经验的开发者提供了深入洞察和实用技巧，涵盖了从基本概念到高级特性的广泛内容。通过阅读本书，读者可以全面提升自己在Java I/O领域的知识和技能。

the exact nature of stringsI'll cover that topic as well, at least briefly. However, this is not a language

tutorial, and the emphasis will always be on the I/O-specific features.

About the Examples

Although many of the examples are toys unlikely to be reused, a few of the classes I develop have real

value. Please feel free to reuse them or any parts of them in your own code; no special permission is

required. Such classes are placed somewhere in the com.elharo package, generally mirroring the java

package hierarchy. For instance, Chapter 2's NullOutputStream class is in the com.elharo.io package.

When working with these classes, don't forget that the compiled .class files must reside in directories

matching their package structure inside your classpath and that you'll have to import them in your own

classes before you can use them. The web page for this book, at http://www.oreilly.com/catalog/javaio2/

, includes a JAR file that can be installed in your classpath.

Conventions Used in This Book

The following formatting conventions are used in this book:

Italic

Used for emphasis and to signify the first use of a term. Italic is also used for commands, filenames, and

URLs.

Constant width

Used in all Java code and generally for anything that you would type literally when programming,

including keywords, data types, constants, method names, variables, class names, and interface names.

Constant width italic

Used as a placeholder to indicate an item that should be replaced with an actual value in your program.

Constant width bold

Used for user input on the command line.

Request for Comments

I enjoy hearing from readers, whether with general comments about how this could be a better book,

specific corrections, or other topics you would like to see covered. You can reach me by sending email

to elharo@metalab.unc.edu

. Please realize, however, that I receive several hundred pieces of email a day and cannot personally

respond to each one.

I'm especially interested in hearing about mistakes. If you find one, I'll post it on my web page for this

book at http://www.cafeaulait.org/books/javaio2/ and on the O'Reilly web site at

http://www.oreilly.com/catalog/javaio2/

. Before reporting errors, please check one of those pages to see if I already know about it and have

posted a fix.

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Chapter 1. Introducing I/O

Input and output, I/O for short, are fundamental to any computer operating system or programming

language. Only theorists find it interesting to write programs that don't require input or produce output. At

the same time, I/O hardly qualifies as one of the more "thrilling" topics in computer science. It's something

in the background, something you use every daybut for most developers, it's not a topic with much sex

appeal.

But in fact, there are plenty of reasons Java programmers should find I/O interesting. Java includes a

particularly rich set of I/O classes in the core API, mostly in the java.io and java.nio

packages. These packages support several different styles of I/O. One distinction is between

byte-oriented I/O, which is handled by input and output streams, and character-I/O, which is handled by

readers and writers. Another distinction is between the old-style stream-based I/O and the new-style

channel- and buffer-based I/O. These all have their place and are appropriate for different needs and use

cases. None of them should be ignored.

Java's I/O libraries

are designed in an abstract way that enables you to read from external data sources and write to external

targets, regardless of the kind of thing you're writing to or reading from. You use the same methods to

read from a file that you do to read from the console or from a network connection. You use the same

methods to write to a file that you do to write to a byte array or a serial port device.

Reading and writing without caring where your data is coming from or where it's going is a very powerful

abstraction. Among other things, this enables you to define I/O streams that automatically compress,

encrypt, and filter from one data format to another. Once you have these tools, programs can send

encrypted data or write zip files with almost no knowledge of what they're doing. Cryptography or

compression can be isolated in a few lines of code that say, "Oh yes, make this a compressed, encrypted

output stream."

In this book, I'll take a thorough look at all parts of Java's I/O facilities. This includes all the different

kinds of streams you can use and the channels and buffers that offer high-performance, high-throughput,

nonblocking operations on servers. We're also going to investigate Java's support for Unicode. We'll

look at Java's powerful facilities for formatting I/O. Finally, we'll look at the various APIs Java provides

for low-level I/O through various devices including serial ports, parallel ports, USB, Bluetooth, and other

hardware you'll find in devices that don't necessarily look like a traditional desktop computer or server.

I won't go so far as to say, "If you've always found I/O boring, this is the book for you!" I will say that if

you do find I/O uninteresting, you probably don't know as much about it as you should. I/O is the means

for communication between software and the outside world. Java provides a powerful and flexible set of

tools for doing this crucial part of the job. Having said that, let's start with the basics.

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1.1. What Is a Stream?

A stream is an ordered sequence of bytes of indeterminate length. Input streams move bytes of data into

a Java program from some generally external source. Output streams move bytes of data from Java to

some generally external target. (In special cases, streams can also move bytes from one part of a Java

program to another.)

The word stream is derived from an analogy between a sequence and a stream of water. An input stream

is like a siphon that sucks up water; an output stream is like a hose that sprays out water. Siphons can be

connected to hoses to move water from one place to another. Sometimes a siphon may run out of water

if it's drawing from a finite source like a bucket. On the other hand, if the siphon is drawing water from a

river, it may well operate indefinitely. So, too, an input stream may read from a finite source of bytes such

as a file or an unlimited source of bytes such as System.in

. Similarly, an output stream may have a definite number of bytes to output or an indefinite number of

bytes.

Input to a Java program can come from many sources. Output can go to many different kinds of

destinations. The power of the stream metaphor is that the differences between these sources and

destinations are abstracted away. All input and output operations are simply treated as streams using the

same classes and the same methods. You don't need to learn a new API for every different kind of

device. The same API that reads files can read network sockets, serial ports, Bluetooth transmissions,

and more.

1.1.1. Where Do Streams Come From?

The first source of input most programmers encounter is System.in. This is the same thing as stdin in

Cgenerally some sort of console window, probably the one in which the Java program was launched. If

input is redirected so the program reads from a file, then System.in is changed as well. For instance, on

Unix, the following command redirects stdin so that when the MessageServer program reads from

System.in, the actual data comes from the file

data.txt instead of from the console:

% java MessageServer < data.txt

The console is also available for output through the static field out in the java.lang.System class, that is,

System.out . This is equivalent to stdout in C parlance and may be redirected in a similar fashion. Finally,

stderr is available as System.err

. This is most commonly used for debugging and printing error messages from inside catch clauses. For

example:

try {

//... do something that might throw an exception

}

catch (Exception ex) {

System.err.println(ex);

}

Both System.out and System.err are print streamsthat is, instances of java.io.PrintStream. These will be

discussed in detail in Chapter 7

Files are another common source of input and destination for output. File input streams provide a stream

of data that starts with the first byte in a file and finishes with the last byte in that file. File output streams

write data into a file, either by erasing the file's contents and starting from the beginning or by appending

data to the file. These will be introduced in Chapter 4

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