An emitter can optionally be configured to filter events at the source.
Event filtering provides a mechanism for reducing event traffic by screening out events that are not important. Each time an event source submits an event to an emitter, the emitter checks the event against the current filter criteria. If the event passes the filter criteria, the emitter sends the event to the event server; otherwise, the emitter discards the event. In any case, an event source cannot change the filter settings, which are configured by an administrator.
The emitter filter is implemented as a separate component called a filter plug-in. The Common Event Infrastructure includes a default filter plug-in, which provides filtering of submitted events based on XPath event selectors. If you want to use a different filter mechanism, you can implement your own filter plug-in.
In the Common Event Infrastructure configuration, each emitter factory is associated with a filter factory. A filter factory is an object used to create instances of a filter plug-in. When you create an emitter using an emitter factory, the emitter is automatically associated with an instance of the specified filter plug-in, which provides filtering of events submitted to that emitter.