深入理解Java NIO.2：Path类的使用

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"Pro.Java.7.NIO.2 是一本关于Java 7中NIO.2扩展的专著，涵盖了Java NIO.2 API的各种核心概念和实用技术。书中的章节内容包括Path类的使用、文件元数据、符号链接与硬链接管理、文件和目录操作、递归操作、WatchService API、随机访问文件、套接字API以及异步通道API等。" Java 7引入的NIO.2（New I/O 2）是对原有NIO（New I/O）框架的重要扩展，它提供了一组更强大且易用的I/O操作接口。其中，Path类是NIO.2的核心组件之一，是进行文件系统操作的基础。Path类代表了文件系统的路径，它抽象出不同操作系统间路径表示的差异，提供了统一的接口来处理路径相关的操作。 Path类的主要功能包括： 1. **创建和解析路径**：Path类可以方便地创建和解析文件路径，支持相对路径和绝对路径的构建，并能够获取路径的各个组成部分。 2. **路径操作**：Path提供了合并（resolve）、相对化（relativize）等方法，使得在处理多个路径时更加灵活。 3. **文件属性**：Path与FileAttributes紧密关联，可以获取或设置文件的基本属性，如文件大小、最后修改时间、权限等。 4. **链接操作**：支持对符号链接和硬链接的创建、查询和管理，这对于文件系统的高级操作至关重要。 5. **文件系统操作**：通过Path，可以进行文件和目录的创建、删除、移动、复制等基本操作。 6. **WatchService API**：Path可以注册到WatchService，监听路径下的文件系统事件，如文件创建、删除或修改，这对于实时监控文件系统变化的应用非常有用。 7. **其他API集成**：Path与FileChannel、BufferedReader/Writer等其他NIO.2类配合使用，实现高效的数据读写。本书详细讲解了如何使用这些功能，帮助开发者深入理解并充分利用Java 7的NIO.2特性，提升文件I/O操作的效率和灵活性。通过阅读此书，读者将能够熟练掌握Path类的使用，以及NIO.2 API在实际开发中的应用。

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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