public interface AclFileAttributeView extends FileOwnerAttributeViewA file attribute view that supports reading or updating a file's Access Control Lists (ACL) or file owner attributes.
ACLs are used to specify access rights to file system objects. An ACL is an ordered list of
access-control-entries, each specifying a
UserPrincipaland the level of access for that user principal. This file attribute view defines the
setAclmethods to read and write ACLs based on the ACL model specified in RFC 3530: Network File System (NFS) version 4 Protocol. This file attribute view is intended for file system implementations that support the NFSv4 ACL model or have a well-defined mapping between the NFSv4 ACL model and the ACL model used by the file system. The details of such mapping are implementation dependent and are therefore unspecified.
This class also extends
FileOwnerAttributeViewso as to define methods to get and set the file owner.
When a file system provides access to a set of
file-systemsthat are not homogeneous then only some of the file systems may support ACLs. The
supportsFileAttributeViewmethod can be used to test if a file system supports ACLs.
InteroperabilityRFC 3530 allows for special user identities to be used on platforms that support the POSIX defined access permissions. The special user identities are "
GROUP@", and "
EVERYONE@". When both the
PosixFileAttributeVieware supported then these special user identities may be included in ACL
entriesthat are read or written. The file system's
UserPrincipalLookupServicemay be used to obtain a
UserPrincipalto represent these special identities by invoking the
Usage Example: Suppose we wish to add an entry to an existing ACL to grant "joe" access:
// lookup "joe" UserPrincipal joe = file.getFileSystem().getUserPrincipalLookupService() .lookupPrincipalByName("joe"); // get view AclFileAttributeView view = Files.getFileAttributeView(file, AclFileAttributeView.class); // create ACE to give "joe" read access AclEntry entry = AclEntry.newBuilder() .setType(AclEntryType.ALLOW) .setPrincipal(joe) .setPermissions(AclEntryPermission.READ_DATA, AclEntryPermission.READ_ATTRIBUTES) .build(); // read ACL, insert ACE, re-write ACL List<AclEntry> acl = view.getAcl(); acl.add(0, entry); // insert before any DENY entries view.setAcl(acl);
Where dynamic access to file attributes is required, the attributes supported by this attribute view are as follows:
Name Type "acl"
Setting the ACL when creating a file
Implementations supporting this attribute view may also support setting the initial ACL when creating a file or directory. The initial ACL may be provided to methods such as
valuethat is the list of
Where an implementation supports an ACL model that differs from the NFSv4 defined ACL model then setting the initial ACL when creating the file must translate the ACL to the model supported by the file system. Methods that create a file should reject (by throwing
IOException) any attempt to create a file that would be less secure as a result of the translation.
String name()Returns the name of the attribute view. Attribute views of this type have the name
List<AclEntry> getAcl() throws IOExceptionReads the access control list.
When the file system uses an ACL model that differs from the NFSv4 defined ACL model, then this method returns an ACL that is the translation of the ACL to the NFSv4 ACL model.
The returned list is modifiable so as to facilitate changes to the existing ACL. The
setAclmethod is used to update the file's ACL attribute.
- an ordered list of
entriesrepresenting the ACL
IOException- if an I/O error occurs
SecurityException- In the case of the default provider, a security manager is installed, and it denies
checkReadmethod denies read access to the file.
void setAcl(List<AclEntry> acl) throws IOExceptionUpdates (replace) the access control list.
Where the file system supports Access Control Lists, and it uses an ACL model that differs from the NFSv4 defined ACL model, then this method must translate the ACL to the model supported by the file system. This method should reject (by throwing
IOException) any attempt to write an ACL that would appear to make the file more secure than would be the case if the ACL were updated. Where an implementation does not support a mapping of
AclEntryType.ALARMentries, then this method ignores these entries when writing the ACL.
If an ACL entry contains a
user-principalthat is not associated with the same provider as this attribute view then
ProviderMismatchExceptionis thrown. Additional validation, if any, is implementation dependent.
If the file system supports other security related file attributes (such as a file
access-permissionsfor example), the updating the access control list may also cause these security related attributes to be updated.
acl- the new access control list
IOException- if an I/O error occurs or the ACL is invalid
SecurityException- In the case of the default provider, a security manager is installed, it denies
checkWritemethod denies write access to the file.