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package java.security;
Abstract class for representing access to a system resource.
All permissions have a name (whose interpretation depends on the subclass),
as well as abstract functions for defining the semantics of the
particular Permission subclass.
Most Permission objects also include an "actions" list that tells the actions that are permitted for the object. For example, for a java.io.FilePermission object, the permission name is the pathname of a file (or directory), and the actions list (such as "read, write") specifies which actions are granted for the specified file (or for files in the specified directory). The actions list is optional for Permission objects, such as java.lang.RuntimePermission, that don't need such a list; you either have the named permission (such as "system.exit") or you don't.
An important method that must be implemented by each subclass is the implies method to compare Permissions. Basically, "permission p1 implies permission p2" means that if one is granted permission p1, one is naturally granted permission p2. Thus, this is not an equality test, but rather more of a subset test.
Permission objects are similar to String objects in that they
are immutable once they have been created. Subclasses should not
provide methods that can change the state of a permission
once it has been created.
Author: Marianne Mueller, Roland Schemers See Also: - Permissions
- PermissionCollection
Since: 1.2
/**
* Abstract class for representing access to a system resource.
* All permissions have a name (whose interpretation depends on the subclass),
* as well as abstract functions for defining the semantics of the
* particular Permission subclass.
*
* <p>Most Permission objects also include an "actions" list that tells the actions
* that are permitted for the object. For example,
* for a {@code java.io.FilePermission} object, the permission name is
* the pathname of a file (or directory), and the actions list
* (such as "read, write") specifies which actions are granted for the
* specified file (or for files in the specified directory).
* The actions list is optional for Permission objects, such as
* {@code java.lang.RuntimePermission},
* that don't need such a list; you either have the named permission (such
* as "system.exit") or you don't.
*
* <p>An important method that must be implemented by each subclass is
* the {@code implies} method to compare Permissions. Basically,
* "permission p1 implies permission p2" means that
* if one is granted permission p1, one is naturally granted permission p2.
* Thus, this is not an equality test, but rather more of a
* subset test.
*
* <P> Permission objects are similar to String objects in that they
* are immutable once they have been created. Subclasses should not
* provide methods that can change the state of a permission
* once it has been created.
*
* @see Permissions
* @see PermissionCollection
*
*
* @author Marianne Mueller
* @author Roland Schemers
* @since 1.2
*/
public abstract class Permission implements Guard, java.io.Serializable {
private static final long serialVersionUID = -5636570222231596674L;
private String name;
Constructs a permission with the specified name.
Params: - name – name of the Permission object being created.
/**
* Constructs a permission with the specified name.
*
* @param name name of the Permission object being created.
*
*/
public Permission(String name) {
this.name = name;
}
Implements the guard interface for a permission. The SecurityManager.checkPermission method is called, passing this permission object as the permission to check. Returns silently if access is granted. Otherwise, throws a SecurityException. Params: - object – the object being guarded (currently ignored).
Throws: - SecurityException – if a security manager exists and its
checkPermission method doesn't allow access.
See Also:
/**
* Implements the guard interface for a permission. The
* {@code SecurityManager.checkPermission} method is called,
* passing this permission object as the permission to check.
* Returns silently if access is granted. Otherwise, throws
* a SecurityException.
*
* @param object the object being guarded (currently ignored).
*
* @throws SecurityException
* if a security manager exists and its
* {@code checkPermission} method doesn't allow access.
*
* @see Guard
* @see GuardedObject
* @see SecurityManager#checkPermission
*
*/
public void checkGuard(Object object) throws SecurityException {
SecurityManager sm = System.getSecurityManager();
if (sm != null) sm.checkPermission(this);
}
Checks if the specified permission's actions are "implied by"
this object's actions.
This must be implemented by subclasses of Permission, as they are the
only ones that can impose semantics on a Permission object.
The implies method is used by the AccessController to determine whether or not a requested permission is implied by another permission that is known to be valid in the current execution context.
Params: - permission – the permission to check against.
Returns: true if the specified permission is implied by this object,
false if not.
/**
* Checks if the specified permission's actions are "implied by"
* this object's actions.
* <P>
* This must be implemented by subclasses of Permission, as they are the
* only ones that can impose semantics on a Permission object.
*
* <p>The {@code implies} method is used by the AccessController to determine
* whether or not a requested permission is implied by another permission that
* is known to be valid in the current execution context.
*
* @param permission the permission to check against.
*
* @return true if the specified permission is implied by this object,
* false if not.
*/
public abstract boolean implies(Permission permission);
Checks two Permission objects for equality.
Do not use the equals method for making access control decisions; use the implies method.
Params: - obj – the object we are testing for equality with this object.
Returns: true if both Permission objects are equivalent.
/**
* Checks two Permission objects for equality.
* <P>
* Do not use the {@code equals} method for making access control
* decisions; use the {@code implies} method.
*
* @param obj the object we are testing for equality with this object.
*
* @return true if both Permission objects are equivalent.
*/
public abstract boolean equals(Object obj);
Returns the hash code value for this Permission object.
The required hashCode behavior for Permission Objects is the following:
- Whenever it is invoked on the same Permission object more than once during an execution of a Java application, the
hashCode method must consistently return the same integer. This integer need not remain consistent from one execution of an application to another execution of the same application. - If two Permission objects are equal according to the
equals method, then calling the hashCode method on each of the two Permission objects must produce the same integer result.
Returns: a hash code value for this object.
/**
* Returns the hash code value for this Permission object.
* <P>
* The required {@code hashCode} behavior for Permission Objects is
* the following:
* <ul>
* <li>Whenever it is invoked on the same Permission object more than
* once during an execution of a Java application, the
* {@code hashCode} method
* must consistently return the same integer. This integer need not
* remain consistent from one execution of an application to another
* execution of the same application.
* <li>If two Permission objects are equal according to the
* {@code equals}
* method, then calling the {@code hashCode} method on each of the
* two Permission objects must produce the same integer result.
* </ul>
*
* @return a hash code value for this object.
*/
public abstract int hashCode();
Returns the name of this Permission. For example, in the case of a java.io.FilePermission, the name will be a pathname. Returns: the name of this Permission.
/**
* Returns the name of this Permission.
* For example, in the case of a {@code java.io.FilePermission},
* the name will be a pathname.
*
* @return the name of this Permission.
*
*/
public final String getName() {
return name;
}
Returns the actions as a String. This is abstract
so subclasses can defer creating a String representation until
one is needed. Subclasses should always return actions in what they
consider to be their
canonical form. For example, two FilePermission objects created via
the following:
perm1 = new FilePermission(p1,"read,write");
perm2 = new FilePermission(p2,"write,read");
both return "read,write" when the getActions method is invoked. Returns: the actions of this Permission.
/**
* Returns the actions as a String. This is abstract
* so subclasses can defer creating a String representation until
* one is needed. Subclasses should always return actions in what they
* consider to be their
* canonical form. For example, two FilePermission objects created via
* the following:
*
* <pre>
* perm1 = new FilePermission(p1,"read,write");
* perm2 = new FilePermission(p2,"write,read");
* </pre>
*
* both return
* "read,write" when the {@code getActions} method is invoked.
*
* @return the actions of this Permission.
*
*/
public abstract String getActions();
Returns an empty PermissionCollection for a given Permission object, or null if one is not defined. Subclasses of class Permission should override this if they need to store their permissions in a particular PermissionCollection object in order to provide the correct semantics when the PermissionCollection.implies method is called. If null is returned, then the caller of this method is free to store permissions of this type in any PermissionCollection they choose (one that uses a Hashtable, one that uses a Vector, etc). Returns: a new PermissionCollection object for this type of Permission, or
null if one is not defined.
/**
* Returns an empty PermissionCollection for a given Permission object, or null if
* one is not defined. Subclasses of class Permission should
* override this if they need to store their permissions in a particular
* PermissionCollection object in order to provide the correct semantics
* when the {@code PermissionCollection.implies} method is called.
* If null is returned,
* then the caller of this method is free to store permissions of this
* type in any PermissionCollection they choose (one that uses a Hashtable,
* one that uses a Vector, etc).
*
* @return a new PermissionCollection object for this type of Permission, or
* null if one is not defined.
*/
public PermissionCollection newPermissionCollection() {
return null;
}
Returns a string describing this Permission. The convention is to
specify the class name, the permission name, and the actions in
the following format: '("ClassName" "name" "actions")', or
'("ClassName" "name")' if actions list is null or empty.
Returns: information about this Permission.
/**
* Returns a string describing this Permission. The convention is to
* specify the class name, the permission name, and the actions in
* the following format: '("ClassName" "name" "actions")', or
* '("ClassName" "name")' if actions list is null or empty.
*
* @return information about this Permission.
*/
public String toString() {
String actions = getActions();
if (actions == null || actions.isEmpty()) { // OPTIONAL
return "(\"" + getClass().getName() + "\" \"" + name + "\")";
} else {
return "(\"" + getClass().getName() + "\" \"" + name +
"\" \"" + actions + "\")";
}
}
}