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 {@link #readAttributes() readAttributes} method is used to read the * file's attributes. The file {@link PosixFileAttributes#owner() owner} is * represented by a {@link UserPrincipal} that is the identity of the file owner * for the purposes of access control. The {@link PosixFileAttributes#group() * group-owner}, represented by a {@link 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 {@link PosixFileAttributes#permissions() permissions} attribute is a * set of access permissions. This file attribute view provides access to the nine * permission defined by the {@link 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 {@link * BasicFileAttributeView} and {@link FileOwnerAttributeView}, and in addition, * the following attributes are supported: *
** ** * *
** * * *Name *Type ** *"permissions" *{@link Set}<{@link PosixFilePermission}> ** * *"group" *{@link GroupPrincipal} *
The {@link Files#getAttribute getAttribute} method may be used to read * any of these attributes, or any of the attributes defined by {@link * BasicFileAttributeView} as if by invoking the {@link #readAttributes * readAttributes()} method. * *
The {@link Files#setAttribute setAttribute} method may be used to update * the file's last modified time, last access time or create time attributes as * defined by {@link BasicFileAttributeView}. It may also be used to update * the permissions, owner, or group-owner as if by invoking the {@link * #setPermissions setPermissions}, {@link #setOwner setOwner}, and {@link * #setGroup 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 {@link Files#createFile createFile} * or {@link Files#createDirectory createDirectory} methods as a {@link * FileAttribute} with {@link FileAttribute#name name} {@code "posix:permissions"} * and a {@link FileAttribute#value value} that is the set of permissions. The * following example uses the {@link PosixFilePermissions#asFileAttribute * asFileAttribute} method to construct a {@code 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 {@link Files#createFile createFile} or {@link
* Files#createDirectory createDirectory} methods. In other words, the file may
* be more secure than requested.
*
* @since 1.7
*/
public interface PosixFileAttributeView
extends BasicFileAttributeView, FileOwnerAttributeView
{
/**
* Returns the name of the attribute view. Attribute views of this type
* have the name {@code "posix"}.
*/
@Override
String name();
/**
* @throws IOException {@inheritDoc}
* @throws SecurityException
* In the case of the default provider, a security manager is
* installed, and it denies
* {@link RuntimePermission}{@code ("accessUserInformation")}
* or its {@link SecurityManager#checkRead(String) checkRead} method
* denies read access to the file.
*/
@Override
PosixFileAttributes readAttributes() throws IOException;
/**
* Updates the file permissions.
*
* @param perms
* the new set of permissions
*
* @throws ClassCastException
* if the sets contains elements that are not of type {@code
* PosixFilePermission}
* @throws IOException
* if an I/O error occurs
* @throws SecurityException
* In the case of the default provider, a security manager is
* installed, and it denies
* {@link RuntimePermission}{@code ("accessUserInformation")}
* or its {@link SecurityManager#checkWrite(String) checkWrite}
* method denies write access to the file.
*/
void setPermissions(Set