程序包 java.nio.file.attribute

接口 PosixFileAttributeView

所有超级接口:

AttributeView, BasicFileAttributeView, FileAttributeView, FileOwnerAttributeView

public interface PosixFileAttributeView
extends BasicFileAttributeView, FileOwnerAttributeView

A file attribute view that provides a view of the file attributes commonly associated with files on file systems used by operating systems that implement the Portable Operating System Interface (POSIX) family of standards.

Operating systems that implement the POSIX family of standards commonly use file systems that have a file owner, group-owner, and related access permissions. This file attribute view provides read and write access to these attributes.

The readAttributes method is used to read the file's attributes. The file PosixFileAttributes#owner() is represented by a UserPrincipal that is the identity of the file owner for the purposes of access control. The PosixFileAttributes#group(), represented by a GroupPrincipal, is the identity of the group owner, where a group is an identity created for administrative purposes so as to determine the access rights for the members of the group.

The PosixFileAttributes#permissions() attribute is a set of access permissions. This file attribute view provides access to the nine permission defined by the PosixFilePermission class. These nine permission bits determine the read, write, and execute access for the file owner, group, and others (others meaning identities other than the owner and members of the group). Some operating systems and file systems may provide additional permission bits but access to these other bits is not defined by this class in this release.

Usage Example: Suppose we need to print out the owner and access permissions of a file:

     Path file = ...
     PosixFileAttributes attrs = Files.getFileAttributeView(file, PosixFileAttributeView.class)
         .readAttributes();
     System.out.format("%s %s%n",
         attrs.owner().getName(),
         PosixFilePermissions.toString(attrs.permissions()));
 

Dynamic Access

Where dynamic access to file attributes is required, the attributes supported by this attribute view are as defined by BasicFileAttributeView and FileOwnerAttributeView, and in addition, the following attributes are supported:

Name	Type
"permissions"	Set<PosixFilePermission>
"group"	GroupPrincipal

The Files#getAttribute method may be used to read any of these attributes, or any of the attributes defined by BasicFileAttributeView as if by invoking the readAttributes() method.

The Files#setAttribute method may be used to update the file's last modified time, last access time or create time attributes as defined by BasicFileAttributeView. It may also be used to update the permissions, owner, or group-owner as if by invoking the setPermissions, setOwner, and setGroup methods respectively.

Setting Initial Permissions

Implementations supporting this attribute view may also support setting the initial permissions when creating a file or directory. The initial permissions are provided to the Files#createFile or Files#createDirectory methods as a FileAttribute with FileAttribute#name "posix:permissions" and a FileAttribute#value that is the set of permissions. The following example uses the PosixFilePermissions#asFileAttribute method to construct a FileAttribute when creating a file:

     Path path = ...
     Set<PosixFilePermission> perms =
         EnumSet.of(OWNER_READ, OWNER_WRITE, OWNER_EXECUTE, GROUP_READ);
     Files.createFile(path, PosixFilePermissions.asFileAttribute(perms));
 

When the access permissions are set at file creation time then the actual value of the permissions may differ that the value of the attribute object. The reasons for this are implementation specific. On UNIX systems, for example, a process has a umask that impacts the permission bits of newly created files. Where an implementation supports the setting of the access permissions, and the underlying file system supports access permissions, then it is required that the value of the actual access permissions will be equal or less than the value of the attribute provided to the Files#createFile or Files#createDirectory methods. In other words, the file may be more secure than requested.

从以下版本开始:

1.7

方法概要

限定符和类型	方法	说明
String	name()	Returns the name of the attribute view.
PosixFileAttributes	readAttributes()	Reads the basic file attributes as a bulk operation.
void	setGroup(GroupPrincipal group)	Updates the file group-owner.
void	setPermissions(Set<PosixFilePermission> perms)	Updates the file permissions.

从接口继承的方法 java.nio.file.attribute.BasicFileAttributeView

setTimes

从接口继承的方法 java.nio.file.attribute.FileOwnerAttributeView

getOwner, setOwner

方法详细资料

name

String name()

Returns the name of the attribute view. Attribute views of this type have the name "posix".

指定者:

name 在接口中 AttributeView

指定者:

name 在接口中 BasicFileAttributeView

指定者:

name 在接口中 FileOwnerAttributeView

返回:

the name of the attribute view

readAttributes

PosixFileAttributes readAttributes()
                            throws IOException

从接口复制的说明: BasicFileAttributeView

Reads the basic file attributes as a bulk operation.

It is implementation specific if all file attributes are read as an atomic operation with respect to other file system operations.

指定者:

readAttributes 在接口中 BasicFileAttributeView

返回:

the file attributes

抛出:

IOException - if an I/O error occurs

SecurityException - In the case of the default provider, a security manager is installed, and it denies RuntimePermission("accessUserInformation") or its SecurityManager#checkRead(String) method denies read access to the file.

setPermissions

void setPermissions(Set<PosixFilePermission> perms)
             throws IOException

Updates the file permissions.

参数:

perms - the new set of permissions

抛出:

ClassCastException - if the sets contains elements that are not of type PosixFilePermission

IOException - if an I/O error occurs

SecurityException - In the case of the default provider, a security manager is installed, and it denies RuntimePermission("accessUserInformation") or its SecurityManager#checkWrite(String) method denies write access to the file.

setGroup

void setGroup(GroupPrincipal group)
       throws IOException

Updates the file group-owner.

参数:

group - the new file group-owner

抛出:

IOException - if an I/O error occurs

SecurityException - In the case of the default provider, and a security manager is installed, it denies RuntimePermission("accessUserInformation") or its SecurityManager#checkWrite(String) method denies write access to the file.