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package java.security.acl;
import java.util.Enumeration;
import java.security.Principal;
/**
* Interface representing an Access Control List (ACL). An Access
* Control List is a data structure used to guard access to
* resources.<p>
*
* 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.<p>
*
* The ACL Entries in each ACL observe the following rules:<p>
*
* <ul> <li>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). <p>
*
* <li>If there is no entry for a particular principal, then the
* principal is considered to have a null (empty) permission set.<p>
*
* <li>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. <p>
*
* <li>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.<p>
*
* </ul>
*
* The <code> java.security.acl </code> package provides the
* interfaces to the ACL and related data structures (ACL entries,
* groups, permissions, etc.), and the <code> sun.security.acl </code>
* classes provide a default implementation of the interfaces. For
* example, <code> java.security.acl.Acl </code> provides the
* interface to an ACL and the <code> sun.security.acl.AclImpl </code>
* class provides the default implementation of the interface.<p>
*
* The <code> java.security.acl.Acl </code> interface extends the
* <code> java.security.acl.Owner </code> 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 <code>addEntry</code> method to add a new ACL entry
* to the ACL.
*
* @see java.security.acl.AclEntry
* @see java.security.acl.Owner
* @see java.security.acl.Acl#getPermissions
*
* @author Satish Dharmaraj
*/
public interface Acl extends Owner {
/**
* Sets the name of this ACL.
*
* @param caller the principal invoking this method. It must be an
* owner of this ACL.
*
* @param name the name to be given to this ACL.
*
* @exception NotOwnerException if the caller principal
* is not an owner of this ACL.
*
* @see #getName
*/
public void setName(Principal caller, String name)
throws NotOwnerException;
/**
* Returns the name of this ACL.
*
* @return the name of this ACL.
*
* @see #setName
*/
public String getName();
/**
* 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.
*
* @param caller the principal invoking this method. It must be an
* owner of this ACL.
*
* @param entry the ACL entry to be added to this ACL.
*
* @return true on success, false if an entry of the same type
* (positive or negative) for the same principal is already
* present in this ACL.
*
* @exception NotOwnerException if the caller principal
* is not an owner of this ACL.
*/
public boolean addEntry(Principal caller, AclEntry entry)
throws NotOwnerException;
/**
* Removes an ACL entry from this ACL.
*
* @param caller the principal invoking this method. It must be an
* owner of this ACL.
*
* @param entry the ACL entry to be removed from this ACL.
*
* @return true on success, false if the entry is not part of this ACL.
*
* @exception NotOwnerException if the caller principal is not
* an owner of this Acl.
*/
public boolean removeEntry(Principal caller, AclEntry entry)
throws NotOwnerException;
/**
* 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
* follows:<p>
*
* <ul>
*
* <li>If there is no entry in this Access Control List for the
* specified principal, an empty permission set is returned.<p>
*
* <li>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.<p>
*
* 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.<p>
*
* 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.
*
* </ul>
*
* @param user the principal whose permission set is to be returned.
*
* @return the permission set specifying the permissions the principal
* is allowed.
*/
public Enumeration<Permission> getPermissions(Principal user);
/**
* Returns an enumeration of the entries in this ACL. Each element in
* the enumeration is of type AclEntry.
*
* @return an enumeration of the entries in this ACL.
*/
public Enumeration<AclEntry> entries();
/**
* 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 <code>getPermissions</code> method.
*
* @param principal the principal, assumed to be a valid authenticated
* Principal.
*
* @param permission the permission to be checked for.
*
* @return true if the principal has the specified permission, false
* otherwise.
*
* @see #getPermissions
*/
public boolean checkPermission(Principal principal, Permission permission);
/**
* Returns a string representation of the
* ACL contents.
*
* @return a string representation of the ACL contents.
*/
public String toString();
}