Apache VFS：基本介绍

http://alartin.iteye.com/blog/92053

Apache VFS提供了一种虚拟文件系统，能够让你通过程序很方便的和位于本地文件系统，FTP文件系统，HTTP文件打交道。
在Apache VFS中核心是 FileObject接口。它代表一个文件，和Java File不同，它具有更多延伸的功能和信息。实现FileObject接口的文件对象有很多：例如AbstractFileObjet抽象类提供了部分FileObject实现。大部分FileObject实现类都继承AbstractFileObject类：

1. LocalFile:(很奇怪为什么不是LocalFileObject)
2. FtpFileObject
3. HttpFileObject
4. SftpFileObject
5. ZipFileObject
6. TarFileObject
7. RamFileObject
8. UrlFileObject
9. DelegateFileObject
10. CompressedFileObject

FileObject代表一个文件，能够用来访问文件内容和结构。文件是以层次结构组织的，每个层次组织形成一个文件系统。一个文件系统就像本地操作系统中的文件系统一样，例如Windows文件系统，或者一个Http服务器，或者一个Zip文件包。

文件有两种类型： 目录和 普通文件。普通文件拥有数据或者说内容，而目录不含有内容，只能包含其他文件，普通文件不能包含其他文件。

文件名
FileObject拥有一个FileName对象，将文件名字作为一个独立的对象处理。文件名是不可变的。文件名对象有很多方法：

1. getBaseName
2. getDepth
3. getExtension
4. getFriendlyURI
5. getParent
6. getPath
7. getRoot
8. 等等

文件内容的读取
注意：和Java File不同的是FileObject拥有一个 FileContent对象，如果想访问文件内容的话，需要使用FileObject.getFileContent()方法，这个方法返回一个FileContent对象。FileContent代表一个文件的内容。
简单的说读取文件内容使用：FileContent. getInputStream()
写内容使用：FileContent. getOutputStream()
FileContent内部有一个 final AbstractFileObject的引用。

FileContent的重要方法有：

1. close 关闭文件内容使用的所有资源，包括所有打开的文件流。当心！！
   
2. get/set Attribute/Attributes: 不能用目前，除非自己重写，其实调用AbstractFileObject的doGet/SetAttribute方法
   
3. getContentInfo 返回一个ContentInfo对象, ContentInfo对象记录了内容的类型和编码信息
   
4. getInputStream 读文件内容
5. getOutputStream 写文件内容
6. isOpen 检查看看该文件有没有打开的文件流
7. getFile 返回FileObject对象
8. get/setLastModifiedTime

文件的操作
基本的文件操作例如创建，删除，重命名，拷贝都可以通过FileObject来完成。

1. copyFrom(FileObject src,FileSelector selector) 从其他地方的源文件拷贝到这个文件中，包括源文件的子文件，有一个文件选择器参数和源文件参数
2. delete() 删除此文件
3. delete(FileSelector selector) 删除符合文件选择器的所有该文件的子文件
4. createFile() 如果这个文件不存在，创建它
5. createFolder() 如果这个目录不存在，创建它

VFS为了支持高级的操作例如和版本控制工具配合，提供了FileOperation对象，不过VFS根本没有任何实现，如果你想玩，自己玩去吧。
在这里批判一下VFS: VFS的开发有些地方非常不合理，例如FileObject号称支持对文件设置属性，后来发现其AbstractFileObject的getAttributes()方法只返回一个空Map,而setAttribute()更离谱，干脆直接抛出不支持的异常。这个功能非常简单啊，如果你需要的话，自己改一下吧。因此，使用VFS时，千万注意这些陷阱，谁让这是开源软件那 ON YOUR OWN RISK!

 

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Commons VFS currently supports the following file systems:

·         FTP

·         Local Files

·         HTTP and HTTPS

·         SFTP

·         Temporary Files

·         Zip, Jar and Tar (uncompressed, tgz or tbz2)

·         gzip and bzip2

·         res

·         ram

·         mime

Things from the sandbox

The following file systems are in development:

·         WebDAV
We can't release WebDAV as we depend on an snapshot, thus it is in our sandbox.

·         CIFS

·         mime

Naming

All filenames are treated as URIs. One of the consequences of this is you have to encode the '%' character using %25.
Depending on the filesystem additional characters are encoded if needet. This is done automatically, but might be reflected in the filename.

Examples

·         file:///somedir/some%25file.txt

Local Files

Provides access to the files on the local physical file system.

URI Format

[file://] absolute-path

Where absolute-pathis a valid absolute file name for the local platform. UNC names are supported under Windows.

Examples

·         file:///home/someuser/somedir

·         file:///C:/Documents and Settings

·         file://///somehost/someshare/afile.txt

·         /home/someuser/somedir

·         c:\program files\some dir

·         c:/program files/some dir

Zip, Jar and Tar

Provides read-only access to the contents of Zip, Jar and Tar files.

URI Format

zip:// arch-file-uri [! absolute-path ]

jar:// arch-file-uri [! absolute-path ]

tar:// arch-file-uri [! absolute-path ]

tgz:// arch-file-uri [! absolute-path ]

tbz2:// arch-file-uri [! absolute-path ]

Where arch-file-uri refers to a file of any supported type, including other zip files. Note: if you would like to use the ! as normal character it must be escaped using %21.
tgz and tbz2 are convenience for tar:gz and tar:bz2.

Examples

·         jar:../lib/classes.jar!/META-INF/manifest.mf

·         zip:http://somehost/downloads/somefile.zip

·         jar:zip:outer.zip!/nested.jar!/somedir

·         jar:zip:outer.zip!/nested.jar!/some%21dir

·         tar:gz:http://anyhost/dir/mytar.tar.gz!/mytar.tar!/path/in/tar/README.txt

·         tgz:file://anyhost/dir/mytar.tgz!/somepath/somefile

gzip and bzip2

Provides read-only access to the contents of gzip and bzip2 files.

URI Format

gz:// compressed-file-uri

bz2:// compressed-file-uri

Where compressed-file-uri refers to a file of any supported type. There is no need to add a ! part to the uri if you read the content of the file you always will get the uncompressed version.

Examples

·         gz:/my/gz/file.gz

HTTP and HTTPS

Provides access to files on an HTTP server.

URI Format

http://[ username [: password ]@] hostname [: port ][ absolute-path ]

https://[ username [: password ]@] hostname [: port ][ absolute-path ]

Examples

·         http://somehost:8080/downloads/somefile.jar

·         http://myusername@somehost/index.html

WebDAV

Provides access to files on a WebDAV server.

URI Format

webdav://[ username [: password ]@] hostname [: port ][ absolute-path ]

Examples

·         webdav://somehost:8080/dist

• WebDAV（“Web-based Distributed Authoring and Versioning” 的缩写）是一个标准HTTP协议的扩展，把web变成一个可读写的媒体，作为当今基本的只读媒体的替代。原理就是目录和文件时可以共享的?都是可读写的对象?通过web。RFCs2518和3253描述了WebDAV/DeltaV 对于HTTP的扩展，存放于（随之有许多其它有用的信息）http://www.webdav.org/。
  
  已经有一些操作系统文件浏览器可以使用WebDAV装配网络目录，在Win32中，Windows浏览器可以像普通共享文件夹一样浏览叫做网络文件夹（只是一个设置好WebDAV的网络位置）的目录，在Mac OS X也有这个能力，就像Nautilus和Konqueror作的（分别对应GNOME和KDE）。 

FTP

Provides access to the files on an FTP server.

URI Format

ftp://[ username [: password ]@] hostname [: port ][ absolute-path ]

Examples

·         ftp://myusername:mypassword@somehost/pub/downloads/somefile.tgz

SFTP

Provides access to the files on an SFTP server (that is, an SSH or SCP server).

URI Format

sftp://[ username [: password ]@] hostname [: port ][ absolute-path ]

Examples

·         sftp://myusername:mypassword@somehost/pub/downloads/somefile.tgz

CIFS

Provides access to the files on a CIFS server, such as a Samba server, or a Windows share.

URI Format

smb://[ username [: password ]@] hostname [: port ][ absolute-path ]

Examples

·         smb://somehost/home

Temporary Files

Provides access to a temporary file system, or scratchpad, that is deleted when Commons VFS shuts down. The temporary file system is backed by a local file system.

URI Format

tmp://[ absolute-path ]

Examples

·         tmp://dir/somefile.txt

res

This is not really a filesystem, it just tries to lookup a resource using javas ClassLoader.getResource() and creates a VFS url for further processing.

URI Format

res://[ path ]

Examples

·         res:path/in/classpath/image.png
might result in jar:file://my/path/to/images.jar!/path/in/classpath/image.png

ram

A filesystem which stores all the data in memory. You can configure the max size and a predicate (FileSelector). The predicate will be used to check if it is allowed to add a given file.

URI Format

ram://[ path ]

Examples

·         ram:///any/path/to/file.txt

mime

This filesystem can read mails and its attachements like archives.
If a part in the parsed mail has no name, a dummy name will be generated. The dummy name is: _body_part_X where X will be replaced by the part number.

URI Format

mime:// mime-file-uri [! absolute-path ]

Examples

·         mime:file:///your/path/mail/anymail.mime!/

·         mime:file:///your/path/mail/anymail.mime!/filename.pdf

·         mime:file:///your/path/mail/anymail.mime!/_body_part_0