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 bits 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 from 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 |
Updates the file group-owner. |
void |
setPermissions |
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.
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