Java Security, 2nd Edition

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, an AccessControlException 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:

package javasec.samples.ch05; import java.security.*; // This is a dummy class; it would usually be the object // that we ...