Pro Java 7 NIO2：探索新抽象类Path与NIO.2 API 功能

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《Pro Java 7 NIO2》是一本深入解析Java 7版新IO（NIO.2）API的专业指南，主要关注NIO.2的核心组件——`java.nio.file.Path`类。该书旨在帮助读者理解并掌握Java平台上的高级IO功能，特别是针对文件和目录操作、元数据管理、符号链接处理、递归操作、监听服务、随机访问文件、套接字API以及异步通道API等。在第1章，"Working with the Path Class"（路径类操作），作者将介绍`Path`类作为NIO.2入口点的重要性。`Path`是抽象的基础类型，它代表了文件和目录的抽象概念，使得应用程序能够以统一的方式处理各种类型的I/O操作，无论是在本地文件系统还是网络文件系统上。通过`Path`，开发者可以执行创建、查找、读取、写入和删除文件或目录等任务，实现更灵活、模块化的编程。第2章"Metadata File Attributes"（元数据文件属性）探讨如何获取和设置文件和目录的元数据，例如所有权、权限、修改日期等，这对于理解和管理文件系统的复杂性至关重要。第3章"Managing Symbolic and Hard Links"（管理符号链接和硬链接）介绍了如何利用NIO.2进行链接操作，这对于文件共享和管理具有重要意义，能够增强程序对文件系统的理解。章节4至9涵盖了更广泛的NIO.2功能，如文件和目录的遍历与操作（Chapter 4: Files and Directories）、递归搜索（Chapter 5: Recursive Operations: Walks）、`WatchService` API用于监控文件变化（Chapter 6: WatchService API）、随机访问文件（Chapter 7: Random Access Files）以及不同类型的网络通信接口（Chapter 8: The Sockets APIs 和 Chapter 9: The Asynchronous Channel API）。最后一章"Important Things to Remember"（重要事项回顾）总结了本书的关键点和最佳实践，确保读者在实际项目中能有效应用所学知识。《Pro Java 7 NIO2》是一本适合Java开发者深入理解并实践NIO.2的实用教程，无论是初学者还是经验丰富的开发人员，都能从中收获提升IO性能和代码可维护性的宝贵技能。通过阅读和实践书中的内容，读者将更好地构建高效、可扩展的Java应用程序。

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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