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 owner is
represented by a UserPrincipal that is the identity of the file owner
for the purposes of access control. The group-owner, 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 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 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 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 createFile
or createDirectory methods as a FileAttribute with name "posix:permissions"
and a value that is the set of permissions. The
following example uses the 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 createFile or createDirectory methods. In other words, the file may
be more secure than requested.
Public Method Summary
| abstract String |
name()
Returns the name of the attribute view.
|
| abstract PosixFileAttributes |
readAttributes()
Reads the basic file attributes as a bulk operation.
|
| abstract void | |
| abstract void |
Inherited Method Summary
Public Methods
public abstract String name ()
Returns the name of the attribute view. Attribute views of this type
have the name "posix".
Returns
- the name of the attribute view
public abstract PosixFileAttributes readAttributes ()
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.
Returns
- the file attributes
Throws
| IOException | |
|---|---|
| SecurityException | In the case of the default provider, a security manager is
installed, and it denies RuntimePermission("accessUserInformation")
or its checkRead method
denies read access to the file.
|
public abstract void setGroup (GroupPrincipal group)
Updates the file group-owner.
Parameters
| group | the new file group-owner |
|---|
Throws
| 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 checkWrite
method denies write access to the file.
|
public abstract void setPermissions (Set<PosixFilePermission> perms)
Updates the file permissions.
Parameters
| perms | the new set of permissions |
|---|
Throws
| 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 checkWrite
method denies write access to the file.
|