Java: Interface PosixFileAttributeView
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All Superinterfaces:
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 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 byBasicFileAttributeView
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 byBasicFileAttributeView
. It may also be used to update the permissions, owner, or group-owner as if by invoking thesetPermissions
, 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.
Since:
1.7
Method Summary
Modifier and Type | Method and Description |
---|---|
String |
Returns the name of the attribute view.
|
PosixFileAttributes |
Reads the basic file attributes as a bulk operation.
|
void |
Updates the file group-owner.
|
void |
Updates the file permissions.
|
Methods inherited from interface java.nio.file.attribute.BasicFileAttributeView
setTimes
Methods inherited from interface java.nio.file.attribute.FileOwnerAttributeView
getOwner, setOwner
Method Detail
name
String name()
"posix"
.Specified by:
name
in interface AttributeView
Specified by:
name
in interface BasicFileAttributeView
Specified by:
name
in interface FileOwnerAttributeView
Returns:
the name of the attribute view
readAttributes
PosixFileAttributes readAttributes() throws IOException
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.
Specified by:
readAttributes
in interface BasicFileAttributeView
Returns:
the file attributes
Throws:
IOException
- if an I/O error occurs
SecurityException
- In the case of the default provider, a security manager is installed, and it deniesRuntimePermission
("accessUserInformation") or its checkRead
method denies read access to the file.
setPermissions
void setPermissions(Set<PosixFilePermission> perms) throws IOException
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 deniesRuntimePermission
("accessUserInformation") or its checkWrite
method denies write access to the file.
setGroup
void setGroup(GroupPrincipal group) throws IOException
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 deniesRuntimePermission
("accessUserInformation") or its checkWrite
method denies write access to the file.
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