Java 7 NIO 2深度探索：Path类与关键操作

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Java 7 NIO 2 是一个关键的Java平台技术，它扩展了Java NIO（New I/O）API，提供了更强大的I/O操作功能。本书以Java 7 NIO 2库为核心，为读者提供了一个全面且易于理解的指南，帮助开发者掌握这一现代化的I/O处理工具。《Java 7 NIO 2》的主要章节包括： 1. **路径处理 (Chapter 1: Working with the Path Class)** - 作为NIO.2 API的起点，`java.nio.file.Path` 类是探索NIO.2的基础。这个抽象类允许开发者以更直观的方式处理文件和目录，它是所有涉及I/O操作的程序中不可或缺的一部分。通过Path类，可以进行路径的创建、解析、连接以及基本的文件系统操作。 2. **元数据和文件属性 (Chapter 2: Metadata File Attributes)** - 这一章节讲解如何获取和设置文件的元数据，如最后修改时间、权限等，并介绍如何检查文件属性，如是否存在、是否可读写等。 3. **符号链接与硬链接管理 (Chapter 3: Managing Symbolic and Hard Links)** - 学习如何处理文件系统中的符号链接和硬链接，这对于实现高级的文件操作和系统级集成非常重要。 4. **文件和目录操作 (Chapter 4: Files and Directories)** - 包括创建、删除、复制、移动文件和目录，以及遍历目录结构。 5. **递归操作：遍历 (Chapter 5: Recursive Operations: Walks)** - 如何使用NIO 2进行深度优先或广度优先的目录遍历，这对于文件搜索和目录结构分析很有用。 6. **WatchService API (Chapter 6: Watch Service APIs)** - 提供了一种机制来监视文件或目录的变化，使得应用程序可以异步响应文件系统的更新事件。 7. **随机访问文件 (Chapter 7: Random Access Files)** - 讲述如何高效地读写数据到文件，支持按偏移量访问，常用于大量数据的处理。 8. **套接字API (Chapter 8: The Sockets APIs)** - 扩展了Java的网络编程能力，支持非阻塞I/O和多路复用，提高了网络通信的性能。 9. **异步通道API (Chapter 9: The Asynchronous Channel API)** - 介绍基于事件驱动的I/O模型，有助于优化并发性能，减少等待时间和提高系统响应速度。 10. **重要事项回顾 (Chapter 10: Important Things to Remember)** - 总结NIO 2的关键概念和最佳实践，为开发者提供复习和巩固学习成果的指南。这本书不仅适合经验丰富的Java开发人员升级他们的技能，也对初次接触NIO 2的读者提供了全面的学习资料。通过阅读本书，开发者将能够充分利用Java 7 NIO 2的强大功能，提升其应用程序的性能和灵活性。

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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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