Package org.apache.commons.configuration2.event

Class BaseEventSource

java.lang.Object
org.apache.commons.configuration2.event.BaseEventSource
All Implemented Interfaces:
EventSource
Direct Known Subclasses:
AbstractConfiguration
public class BaseEventSource extends Object implements EventSource

A base class for objects that can generate configuration events.

This class implements functionality for managing a set of event listeners that can be notified when an event occurs. It can be extended by configuration classes that support the event mechanism. In this case these classes only need to call the fireEvent() method when an event is to be delivered to the registered listeners.

Adding and removing event listeners can happen concurrently to manipulations on a configuration that cause events. The operations are synchronized.

With the detailEvents property the number of detail events can be controlled. Some methods in configuration classes are implemented in a way that they call other methods that can generate their own events. One example is the setProperty() method that can be implemented as a combination of clearProperty() and addProperty(). With detailEvents set to true, all involved methods will generate events (i.e. listeners will receive property set events, property clear events, and property add events). If this mode is turned off (which is the default), detail events are suppressed, so only property set events will be received. Note that the number of received detail events may differ for different configuration implementations. BaseHierarchicalConfiguration for instance has a custom implementation of setProperty(), which does not generate any detail events.

In addition to "normal" events, error events are supported. Such events signal an internal problem that occurred during access of properties. They are handled via the regular EventListener interface, but there are special event types defined by ConfigurationErrorEvent. The fireError() method can be used by derived classes to send notifications about errors to registered observers.

Since:
1.3

  • Constructor Details

    • BaseEventSource

      public BaseEventSource()
      Creates a new instance of BaseEventSource.

  • Method Details

    • addEventListener

      public <T extends Event> void addEventListener(EventType<T> eventType, EventListener<? super T> listener)
      Description copied from interface: EventSource
      Adds an event listener for the specified event type. This listener is notified about events of this type and all its sub types.
      Specified by:
      addEventListener in interface EventSource
      Type Parameters:
      T - the type of events processed by this listener
      Parameters:
      eventType - the event type (must not be null)
      listener - the listener to be registered (must not be null)

    • clearErrorListeners

      public void clearErrorListeners()
      Removes all registered error listeners.
      Since:
      1.4

    • clearEventListeners

      public void clearEventListeners()
      Removes all registered event listeners.

    • clone

      protected Object clone() throws CloneNotSupportedException
      Overrides the clone() method to correctly handle so far registered event listeners. This implementation ensures that the clone will have empty event listener lists, i.e. the listeners registered at an BaseEventSource object will not be copied.
      Overrides:
      clone in class Object
      Returns:
      the cloned object
      Throws:
      CloneNotSupportedException - if cloning is not allowed
      Since:
      1.4

    • copyEventListeners

      public void copyEventListeners(BaseEventSource source)
      Copies all event listener registrations maintained by this object to the specified BaseEventSource object.
      Parameters:
      source - the target source for the copy operation (must not be null)
      Throws:
      IllegalArgumentException - if the target source is null
      Since:
      2.0

    • createErrorEvent

      protected ConfigurationErrorEvent createErrorEvent(EventType<? extends ConfigurationErrorEvent> type, EventType<?> opType, String propName, Object propValue, Throwable ex)
      Creates a ConfigurationErrorEvent object based on the passed in parameters. This is called by fireError() if it decides that an event needs to be generated.
      Parameters:
      type - the event's type
      opType - the operation type related to this error
      propName - the name of the affected property (can be null)
      propValue - the value of the affected property (can be null)
      ex - the Throwable object that caused this error event
      Returns:
      the event object

    • createEvent

      protected <T extends ConfigurationEvent> ConfigurationEvent createEvent(EventType<T> type, String propName, Object propValue, boolean before)
      Creates a ConfigurationEvent object based on the passed in parameters. This method is called by fireEvent() if it decides that an event needs to be generated.
      Type Parameters:
      T - the type of the event to be created
      Parameters:
      type - the event's type
      propName - the name of the affected property (can be null)
      propValue - the value of the affected property (can be null)
      before - the before update flag
      Returns:
      the newly created event object

    • fireError

      public <T extends ConfigurationErrorEvent> void fireError(EventType<T> eventType, EventType<?> operationType, String propertyName, Object propertyValue, Throwable cause)
      Creates an error event object and delivers it to all registered error listeners of a matching type.
      Type Parameters:
      T - the event type
      Parameters:
      eventType - the event's type
      operationType - the type of the failed operation
      propertyName - the name of the affected property (can be null)
      propertyValue - the value of the affected property (can be null)
      cause - the Throwable object that caused this error event

    • fireEvent

      protected <T extends ConfigurationEvent> void fireEvent(EventType<T> type, String propName, Object propValue, boolean before)
      Creates an event object and delivers it to all registered event listeners. The method checks first if sending an event is allowed (making use of the detailEvents property), and if listeners are registered.
      Type Parameters:
      T - the type of the event to be fired
      Parameters:
      type - the event's type
      propName - the name of the affected property (can be null)
      propValue - the value of the affected property (can be null)
      before - the before update flag

    • getEventListenerRegistrations

      public List<EventListenerRegistrationData<?>> getEventListenerRegistrations()
      Gets a list with all EventListenerRegistrationData objects currently contained for this event source. This method allows access to all registered event listeners, independent on their type.
      Returns:
      a list with information about all registered event listeners

    • getEventListeners

      public <T extends Event> Collection<EventListener<? super T>> getEventListeners(EventType<T> eventType)
      Gets a collection with all event listeners of the specified event type that are currently registered at this object.
      Type Parameters:
      T - the event type
      Parameters:
      eventType - the event type object
      Returns:
      a collection with the event listeners of the specified event type (this collection is a snapshot of the currently registered listeners; it cannot be manipulated)

    • isDetailEvents

      public boolean isDetailEvents()
      Returns a flag whether detail events are enabled.
      Returns:
      a flag if detail events are generated

    • removeEventListener

      public <T extends Event> boolean removeEventListener(EventType<T> eventType, EventListener<? super T> listener)
      Description copied from interface: EventSource
      Removes the event listener registration for the given event type and listener. An event listener instance may be registered multiple times for different event types. Therefore, when removing a listener the event type of the registration in question has to be specified. The return value indicates whether a registration was removed. A value of false means that no such combination of event type and listener was found.
      Specified by:
      removeEventListener in interface EventSource
      Type Parameters:
      T - the type of events processed by this listener
      Parameters:
      eventType - the event type
      listener - the event listener to be removed
      Returns:
      a flag whether a listener registration was removed

    • setDetailEvents

      public void setDetailEvents(boolean enable)
      Determines whether detail events should be generated. If enabled, some methods can generate multiple update events. Note that this method records the number of calls, i.e. if for instance setDetailEvents(false) was called three times, you will have to invoke the method as often to enable the details.
      Parameters:
      enable - a flag if detail events should be enabled or disabled