Guarded Objects
The notion of permissions and the
access controller can be encapsulated into a single object: a guarded
object, which is implemented by the
GuardedObject
class
(java.security.GuardedObject
). This
class allows you to embed another object within it in such a way that
all access to the object will first have to go through a guard
(which, typically, is the access controller).
There are two methods in the GuardedObject class:
- public GuardedObject(Object o, Guard g)
Create a guarded object. The given object is embedded within the guarded object; access to the embedded object will not be granted unless the guard allows it.
- public Object getObject() ★
Return the embedded object. The
checkGuard()
method of the guard is first called; if the guard prohibits access to the embedded object, anAccessControlException
will be thrown. Otherwise, the embedded object is returned.
The guard can be any class that implements the
Guard
interface
(java.security.Guard
). This interface has a
single method:
- public void checkGuard(Object o) ★
See if access to the given object should be granted. If access is not granted, this method should throw an
AccessControlException
; otherwise it should silently return.
Although you can write your own guards, the
Permission
class already implements the guard interface. Hence, any permission
can be used to guard an object as follows:
public class GuardTest ...
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