Java 1.7 NIO.2 深入解析：Path类与异步I/O

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"java1.7_nio2_aio_book" 是一本关于Java 1.7版本新特性，特别是NIO.2（JSR203）和AIO（异步I/O）技术的书籍。这本书详细介绍了如何利用这些新特性进行高效的I/O操作。书中的内容涵盖了从基础到高级的各种主题，旨在帮助开发者充分利用Java 1.7引入的Path类和其他相关API。以下是各章节的主要知识点： 1. **Chapter 1: Working with the Path Class** - Path类是NIO.2的核心，它提供了一种统一的方式来表示文件路径，无论是在不同的操作系统上。 - 介绍Path类的基本用法，如创建、解析、比较和转换路径。 - 解释如何使用Path类进行文件操作，如读取、写入、删除和重命名。 2. **Chapter 2: Metadata File Attributes** - 讨论获取和修改文件元数据的方法，包括文件大小、最后访问时间、权限等属性。 - 介绍如何处理文件的权限和所有权。 3. **Chapter 3: Manage Symbolic and Hard Links** - 详细讲解如何在Java中创建和管理符号链接和硬链接，这对于处理复杂的文件系统结构至关重要。 4. **Chapter 4: Files and Directories** - 阐述文件和目录的创建、删除、移动等操作，以及遍历目录树的方法。 - 探讨文件系统操作的并发控制和安全问题。 5. **Chapter 5: Recursive Operations: Walks** - 介绍如何递归地遍历文件系统，包括文件和目录的深度优先和广度优先搜索。 6. **Chapter 6: WatchService API** - 解析WatchService API，用于监听文件系统事件，如文件或目录的创建、删除和修改。 - 展示如何实现文件系统监控功能，以实时响应文件系统的变动。 7. **Chapter 7: RandomAccessFiles** - 讲解RandomAccessFile类，用于随机访问文件，支持读写操作。 - 介绍如何高效地定位和操作大文件中的特定位置。 8. **Chapter 8: The Sockets API** - 深入理解Java的Socket API，包括TCP和UDP通信。 - 展示如何创建和管理网络连接，发送和接收数据。 9. **Chapter 9: The AsynchronousChannel API** - 详述AIO（异步I/O）的概念，它是Java 1.7引入的重要特性。 - 介绍AsynchronousChannelGroup、AsynchronousServerSocketChannel和AsynchronousSocketChannel的使用，实现非阻塞I/O操作。 10. **Chapter 10: Important Things to Remember** - 提供关键知识点的总结，强调在实际开发中需要注意的要点和最佳实践。通过本书，读者可以全面了解Java 1.7的NIO.2和AIO特性，提升对文件系统操作和网络通信的理解，从而编写出更高效、更可靠的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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