| The UnresolvedPermission class is used to hold Permissions that
were "unresolved" when the Policy was initialized.
An unresolved permission is one whose actual Permission class
does not yet exist at the time the Policy is initialized (see below).
The policy for a Java runtime (specifying
which permissions are available for code from various principals)
is represented by a Policy object.
Whenever a Policy is initialized or refreshed, Permission objects of
appropriate classes are created for all permissions
allowed by the Policy.
Many permission class types
referenced by the policy configuration are ones that exist
locally (i.e., ones that can be found on CLASSPATH).
Objects for such permissions can be instantiated during
Policy initialization. For example, it is always possible
to instantiate a java.io.FilePermission, since the
FilePermission class is found on the CLASSPATH.
Other permission classes may not yet exist during Policy
initialization. For example, a referenced permission class may
be in a JAR file that will later be loaded.
For each such class, an UnresolvedPermission is instantiated.
Thus, an UnresolvedPermission is essentially a "placeholder"
containing information about the permission.
Later, when code calls AccessController.checkPermission
on a permission of a type that was previously unresolved,
but whose class has since been loaded, previously-unresolved
permissions of that type are "resolved". That is,
for each such UnresolvedPermission, a new object of
the appropriate class type is instantiated, based on the
information in the UnresolvedPermission.
To instantiate the new class, UnresolvedPermission assumes
the class provides a zero, one, and/or two-argument constructor.
The zero-argument constructor would be used to instantiate
a permission without a name and without actions.
A one-arg constructor is assumed to take a String
name as input, and a two-arg constructor is assumed to take a
String name and String actions
as input. UnresolvedPermission may invoke a
constructor with a null name and/or actions.
If an appropriate permission constructor is not available,
the UnresolvedPermission is ignored and the relevant permission
will not be granted to executing code.
The newly created permission object replaces the
UnresolvedPermission, which is removed.
See Also: java.security.Permission
See Also: java.security.Permissions
See Also: java.security.PermissionCollection
See Also: java.security.Policy
version:
1.17 00/02/02
author:
Roland Schemers | 