Java 7 NIO.2 深入解析

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"Pro Java 7 NIO.2" 是一本深入探讨Java 7中NIO.2（也称为JSR203）新特性的专业书籍，它为开发者提供了全面的指南，涵盖了如何有效利用这些新特性进行文件操作。本书内容丰富，包括多个章节，详细介绍了NIO.2中的核心概念和实用技术。以下是各章节的主要知识点概述： 1. **关于Path类的工作**：Path类是NIO.2的入口点，它是所有文件系统操作的基础。这个抽象类提供了一种与平台无关的方式来表示文件系统的路径，并提供了创建、解析、比较和操作路径的方法。开发者可以通过Path类进行文件操作，如读取、写入、删除、重命名文件等。 2. **元数据和文件属性**：在第2章，书中讲解了如何获取和修改文件的元数据，如文件大小、最后访问时间、权限等。这些信息对于管理文件系统至关重要。 3. **符号链接和硬链接的管理**：第3章涉及了符号链接和硬链接的概念，它们允许文件系统中的一个路径指向另一个文件或目录。书中详细解释了如何创建、查询和处理这两种链接类型。 4. **文件和目录的操作**：第4章介绍如何对文件和目录进行基本操作，如创建、删除、移动、遍历目录树等。这些操作是任何文件系统操作的核心部分。 5. **递归操作：文件遍历**：在第5章，读者将学习到如何使用`Files.walk()`和`Files.find()`方法进行深度优先或广度优先的文件系统遍历，这对于处理大量文件或需要查找特定文件的场景非常有用。 6. **WatchService API**：第6章讲解了WatchService，这是一个观察文件系统变化的接口。通过注册监听器，可以实时响应文件或目录的创建、删除和修改事件，从而实现文件系统的动态监控。 7. **随机访问文件**：第7章介绍了随机访问文件，允许开发者在文件的任意位置读写数据，这在处理大文件时特别有用。 8. **套接字APIs**：第8章深入到网络I/O，涵盖了Socket和ServerSocket API，用于建立客户端-服务器通信，发送和接收数据。 9. **异步通道API**：第9章讨论了AsynchronousChannelGroup和AsynchronousFileChannel，它们支持非阻塞I/O，可以在多线程环境下高效处理并发读写任务。 10. **重要事项回顾**：最后一章总结了使用NIO.2时需要注意的关键点，帮助开发者避免常见的陷阱和优化代码性能。此外，书中的作者简介、技术审阅者信息、致谢以及索引等补充内容为读者提供了完整的阅读体验。这本书对于希望深入了解Java 7 NIO.2特性的开发者来说，是一份宝贵的参考资料。

CHAPTER 2 ■

METADATA FILE ATTRIBUTES

You can test a particular view on a file store by calling the FileStore.supportsFileAttributeView()

method. You can pass the desired view as a String or as a class name. The following code checks

whether the basic view is supported by all the available file stores:

import java.nio.file.FileStore;

import java.nio.file.FileSystem;

import java.nio.file.FileSystems;

import java.nio.file.attribute.BasicFileAttributeView;

…

FileSystem fs = FileSystems.getDefault();

for (FileStore store : fs.getFileStores()) {

boolean supported = store.supportsFileAttributeView(BasicFileAttributeView.class);

System.out.println(store.name() + " ---" + supported);

}

Moreover, you can check if a file store in which a particular file resides supports a single view, as

shown in this example:

import java.io.IOException;

import java.nio.file.FileStore;

import java.nio.file.Files;

import java.nio.file.Path;

import java.nio.file.Paths;

…

Path path = Paths.get("C:/rafaelnadal/tournaments/2009", "BNP.txt");

try {

FileStore store = Files.getFileStore(path);

boolean supported = store.supportsFileAttributeView("basic");

System.out.println(store.name() + " ---" + supported);

} catch (IOException e) {

System.err.println(e);

}

Now that you can determine which views are supported on your file system, it is time to dig deeper

and explore each view’s attributes, starting with the basic view.

Basic View

Most file system implementations support a set of common attributes (size, creation time, last accessed

time, last modified time, etc.). These attributes are grouped into a view named BasicFileAttributeView

and can be extracted and set as described in the following subsections.

Get Bulk Attributes with readAttributes()

You can extract attributes in bulk using the readAttributes() method as follows (the varargs argument

currently supports the LinkOption.NOFOLLOW_LINKS enum—do not follow symbolic links):

import java.io.IOException;

import java.nio.file.Files;

import java.nio.file.Path;

CHAPTER 2 ■ METADATA FILE ATTRIBUTES

Updating the file’s last modified time can also be accomplished with the setAttribute() method.

Actually, this method may be used to update the file’s last modified time, last access time, or create time

attributes as if by invoking the setTimes() method:

import static java.nio.file.LinkOption.NOFOLLOW_LINKS;

…

try {

Files.setAttribute(path, "basic:lastModifiedTime", fileTime, NOFOLLOW_LINKS);

Files.setAttribute(path, "basic:creationTime", fileTime, NOFOLLOW_LINKS);

Files.setAttribute(path, "basic:lastAccessTime", fileTime, NOFOLLOW_LINKS);

} catch (IOException e) {

System.err.println(e);

}

Obviously, now you have to extract the three attributes’ values to see the changes. You can do so by

using the getAttribute() method:

try {

FileTime lastModifiedTime = (FileTime)Files.getAttribute(path,

"basic:lastModifiedTime", NOFOLLOW_LINKS);

FileTime creationTime = (FileTime)Files.getAttribute(path,

"basic:creationTime", NOFOLLOW_LINKS);

FileTime lastAccessTime = (FileTime)Files.getAttribute(path,

"basic:lastAccessTime", NOFOLLOW_LINKS);

System.out.println("New last modified time: " + lastModifiedTime);

System.out.println("New creation time: " + creationTime);

System.out.println("New last access time: " + lastAccessTime);

} catch (IOException e) {

System.err.println(e);

}

DOS View

Specific to the DOS file system (or Samba), the DosFileAttributeView view extends the basic view with

the DOS attributes (which means that you can access the basic view directly from DOS view). There are

four attributes, which are mapped by the following methods:

• isReadOnly(): Returns the readonly attribute’s value (if true, the file can’t be

deleted or updated)

• isHidden(): Returns the hidden attribute’s value (if true, the file is not visible to the

users)

• isArchive(): Returns the archive attribute’s value (specific to backup programs)

• isSystem(): Returns the system attribute’s value (if true, the file belongs to the

operating system)

The following listing extracts in bulk the preceding four attributes for a given path:

import java.io.IOException;

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Java 7 NIO.2 深入解析

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