[CONFIGURATION-143] [configuration] Support event listeners for configurations

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 1.2
• Fix Version/s: 1.4

Environment

Operating System: other
Platform: Other

• Bugzilla Id: 38929
• Assignee: Unassigned
• Reporter: Oliver Heger
• Created: 11/Mar/06 23:26
• Updated: 22/Aug/09 19:36
• Resolved: 10/Jan/07 20:20

Description

I would like to suggest creating a ConfigurationEvent class and a
ConfigurationEventListener interface for monitoring changes on configurations.

AbstractConfiguration could act as an event source allowing listeners to
register itself at an instance. Whenever this instance is modified a
notification is sent out to all registered listeners.

The event class could contain

• a reference to the affected Configuration object
• an ID about the type of the event (e.g. property added, property removed,
  configuration cleared etc.)
• the name of the affected property if applicable
• the value of the affected property if applicable

The listener interface could be quite simple and contain only a single method:
void configurationChanged(ConfigurationEvent event);

While an implementation should not be too complicated some details need to be
cleared:

• ATM as AbstractConfiguration is implemented an operation could cause multiple
  events. For instance setProperty() is implemented as calling clearProperty() and
  then addProperty(). Should this be caught and treated as a single event?

• Should a reload of a file based configuration cause an event? Could this be
  problematic if a called listener tries to access the configuration?