深入理解Java 7 NIO.2 API

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"Pro Java 7 NIO.2" 是一本深入探讨Java 7中新的I/O API（也称为JSR 203）的专业书籍，重点介绍了Path类的使用和其他相关特性。这本书的主要内容包括： 1. **Path类的工作方式** (Chapter1: Working with the Path Class) - Path类是NIO.2 API的核心，它提供了一种抽象的方式来表示文件系统中的路径。通过Path，开发者可以方便地创建、解析、操作和比较文件路径。 - 这一章可能涵盖了如何创建Path对象，获取路径组件，以及进行路径操作，如合并和解析。 2. **元数据和文件属性** (Chapter2: Metadata File Attributes) - 讨论了如何获取文件的元数据，例如文件大小、最后访问时间、修改时间等，这些都是通过Path类和相关API实现的。 3. **符号链接和硬链接管理** (Chapter3: Manage Symbolic and Hard Links) - 介绍如何在Java中创建和操作符号链接及硬链接，这在处理文件系统结构时非常有用。 4. **文件和目录操作** (Chapter4: Files and Directories) - 这一章可能涵盖了创建、删除、移动和复制文件及目录的API，以及检查文件是否存在或是否可读写等权限操作。 5. **递归操作：遍历** (Chapter5: Recursive Operations: Walks) - 详细讲解如何遍历目录树，这对于处理大量文件或执行递归任务时尤其重要。 6. **WatchService API** (Chapter6: WatchService API) - WatchService API允许程序监视文件系统事件，如文件创建、删除或修改，这在实时监控和响应文件系统变化的场景中很有用。 7. **随机访问文件** (Chapter7: RandomAccessFiles) - 随机访问文件允许在文件的任意位置读写数据，这一章可能涉及如何高效地处理大文件和定位到特定数据。 8. **套接字APIs** (Chapter8: The SocketsAPIs) - 讲解如何使用NIO.2中的套接字API进行网络通信，包括TCP和UDP连接。 9. **异步通道API** (Chapter9: The AsynchronousChannelAPI) - 异步I/O允许非阻塞操作，提高性能，特别是在高并发场景下。这一章可能涵盖异步文件读写、网络通信等。 10. **重要事项回顾** (Chapter10: Important Things to Remember) - 对整个NIO.2 API的关键点进行总结，帮助读者巩固和应用所学知识。 11. **索引** (Index) - 提供了完整的书目索引，方便查找特定主题。这本书对于任何希望深入理解Java 7 I/O功能，特别是NIO.2的开发者来说都是宝贵的资源。通过学习，开发者能够编写更高效、更健壮的I/O密集型应用程序。

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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