Interface representing an Access Control List (ACL). An Access
Control List is a data structure used to guard access to
An ACL can be thought of as a data structure with multiple ACL
entries. Each ACL entry, of interface type AclEntry, contains a
set of permissions associated with a particular principal. (A
principal represents an entity such as an individual user or a
group). Additionally, each ACL entry is specified as being either
positive or negative. If positive, the permissions are to be
granted to the associated principal. If negative, the permissions
are to be denied.
The ACL Entries in each ACL observe the following rules:
Each principal can have at most one positive ACL entry and
one negative entry; that is, multiple positive or negative ACL
entries are not allowed for any principal. Each entry specifies
the set of permissions that are to be granted (if positive) or
denied (if negative).
If there is no entry for a particular principal, then the
principal is considered to have a null (empty) permission set.
If there is a positive entry that grants a principal a
particular permission, and a negative entry that denies the
principal the same permission, the result is as though the
permission was never granted or denied.
Individual permissions always override permissions of the
group(s) to which the individual belongs. That is, individual
negative permissions (specific denial of permissions) override the
groups' positive permissions. And individual positive permissions
override the groups' negative permissions.
The java.security.acl package provides the
interfaces to the ACL and related data structures (ACL entries,
groups, permissions, etc.), and the sun.security.acl
classes provide a default implementation of the interfaces. For
example, java.security.acl.Acl provides the
interface to an ACL and the sun.security.acl.AclImpl
class provides the default implementation of the interface.
The java.security.acl.Acl interface extends the
java.security.acl.Owner interface. The Owner
interface is used to maintain a list of owners for each ACL. Only
owners are allowed to modify an ACL. For example, only an owner can
call the ACL's addEntry method to add a new ACL entry
to the ACL.
Adds an ACL entry to this ACL. An entry associates a principal
(e.g., an individual or a group) with a set of
permissions. Each principal can have at most one positive ACL
entry (specifying permissions to be granted to the principal)
and one negative ACL entry (specifying permissions to be
denied). If there is already an ACL entry of the same type
(negative or positive) already in the ACL, false is returned.
caller - the principal invoking this method. It must be an
owner of this ACL.
entry - the ACL entry to be added to this ACL.
true on success, false if an entry of the same type
(positive or negative) for the same principal is already
present in this ACL.
Returns an enumeration for the set of allowed permissions for the
specified principal (representing an entity such as an individual or
a group). This set of allowed permissions is calculated as
If there is no entry in this Access Control List for the
specified principal, an empty permission set is returned.
Otherwise, the principal's group permission sets are determined.
(A principal can belong to one or more groups, where a group is a
group of principals, represented by the Group interface.)
The group positive permission set is the union of all
the positive permissions of each group that the principal belongs to.
The group negative permission set is the union of all
the negative permissions of each group that the principal belongs to.
If there is a specific permission that occurs in both
the positive permission set and the negative permission set,
it is removed from both.
The individual positive and negative permission sets are also
determined. The positive permission set contains the permissions
specified in the positive ACL entry (if any) for the principal.
Similarly, the negative permission set contains the permissions
specified in the negative ACL entry (if any) for the principal.
The individual positive (or negative) permission set is considered
to be null if there is not a positive (negative) ACL entry for the
principal in this ACL.
The set of permissions granted to the principal is then calculated
using the simple rule that individual permissions always override
the group permissions. That is, the principal's individual negative
permission set (specific denial of permissions) overrides the group
positive permission set, and the principal's individual positive
permission set overrides the group negative permission set.
user - the principal whose permission set is to be returned.
the permission set specifying the permissions the principal
Checks whether or not the specified principal has the specified
permission. If it does, true is returned, otherwise false is returned.
More specifically, this method checks whether the passed permission
is a member of the allowed permission set of the specified principal.
The allowed permission set is determined by the same algorithm as is
used by the getPermissions method.
principal - the principal, assumed to be a valid authenticated
permission - the permission to be checked for.
true if the principal has the specified permission, false