AttributeView
, BasicFileAttributeView
, FileAttributeView
, FileOwnerAttributeView
public interface PosixFileAttributeView extends BasicFileAttributeView, FileOwnerAttributeView
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()));
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.
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.
Modifier and Type | Method | Description |
---|---|---|
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.
|
setTimes
getOwner, setOwner
String name()
"posix"
.name
in interface AttributeView
name
in interface BasicFileAttributeView
name
in interface FileOwnerAttributeView
PosixFileAttributes readAttributes() throws IOException
BasicFileAttributeView
It is implementation specific if all file attributes are read as an atomic operation with respect to other file system operations.
readAttributes
in interface BasicFileAttributeView
IOException
- if an I/O error occursSecurityException
- 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.void setPermissions(Set<PosixFilePermission> perms) throws IOException
perms
- the new set of permissionsClassCastException
- if the sets contains elements that are not of type
PosixFilePermission
IOException
- if an I/O error occursSecurityException
- 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.void setGroup(GroupPrincipal group) throws IOException
group
- the new file group-ownerIOException
- if an I/O error occursSecurityException
- 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. Submit a bug or feature
For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
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DRAFT 9-internal+0-adhoc.mlchung.jdk9-jdeps