DomainCombiner provides a means to dynamically
* update the ProtectionDomains associated with the current
* AccessControlContext.
*
* A DomainCombiner is passed as a parameter to the
* appropriate constructor for AccessControlContext.
* The newly constructed context is then passed to the
* AccessController.doPrivileged(..., context) method
* to bind the provided context (and associated DomainCombiner)
* with the current execution Thread. Subsequent calls to
* AccessController.getContext or
* AccessController.checkPermission
* cause the DomainCombiner.combine to get invoked.
*
*
The combine method takes two arguments. The first argument represents
* an array of ProtectionDomains from the current execution Thread,
* since the most recent call to AccessController.doPrivileged.
* If no call to doPrivileged was made, then the first argument will contain
* all the ProtectionDomains from the current execution Thread.
* The second argument represents an array of inherited ProtectionDomains,
* which may be null. ProtectionDomains may be inherited
* from a parent Thread, or from a privileged context. If no call to
* doPrivileged was made, then the second argument will contain the
* ProtectionDomains inherited from the parent Thread. If one or more calls
* to doPrivileged were made, and the most recent call was to
* doPrivileged(action, context), then the second argument will contain the
* ProtectionDomains from the privileged context. If the most recent call
* was to doPrivileged(action), then there is no privileged context,
* and the second argument will be null.
*
*
The combine method investigates the two input arrays
* of ProtectionDomains and returns a single array containing the updated
* ProtectionDomains. In the simplest case, the combine
* method merges the two stacks into one. In more complex cases,
* the combine method returns a modified
* stack of ProtectionDomains. The modification may have added new
* ProtectionDomains, removed certain ProtectionDomains, or simply
* updated existing ProtectionDomains. Re-ordering and other optimizations
* to the ProtectionDomains are also permitted. Typically the
* combine method bases its updates on the information
* encapsulated in the DomainCombiner.
*
*
After the AccessController.getContext method
* receives the combined stack of ProtectionDomains back from
* the DomainCombiner, it returns a new
* AccessControlContext that has both the combined ProtectionDomains
* as well as the DomainCombiner.
*
* @see AccessController
* @see AccessControlContext
* @version 1.7, 12/19/03
*/
public interface DomainCombiner {
/**
* Modify or update the provided ProtectionDomains.
* ProtectionDomains may be added to or removed from the given
* ProtectionDomains. The ProtectionDomains may be re-ordered.
* Individual ProtectionDomains may be may be modified (with a new
* set of Permissions, for example).
*
*
*
* @param currentDomains the ProtectionDomains associated with the
* current execution Thread, up to the most recent
* privileged ProtectionDomain.
* The ProtectionDomains are are listed in order of execution,
* with the most recently executing ProtectionDomain
* residing at the beginning of the array. This parameter may
* be null if the current execution Thread
* has no associated ProtectionDomains.
*
* @param assignedDomains an array of inherited ProtectionDomains.
* ProtectionDomains may be inherited from a parent Thread,
* or from a privileged AccessControlContext.
* This parameter may be null
* if there are no inherited ProtectionDomains.
*
* @return a new array consisting of the updated ProtectionDomains,
* or null.
*/
ProtectionDomain[] combine(ProtectionDomain[] currentDomains,
ProtectionDomain[] assignedDomains);
}