Esper is an open-source Java CEP engine. Esper, like OSWorkflow needs to be embedded inside your application, it doesn't run in standalone mode. Esper is optimized for the processing of very large volume of events in real time.
This section describes the three most important concepts in Esper architecture: events, patterns, and listeners.
Esper, like every CEP engine analyzes an event stream and detects relevant events, matching them with user-defined patterns. For Esper, these events are regular JavaBeans and the patterns are represented in EQL. EQL is a special language designed for pattern matching and its syntax is very similar to that of SQL.
The patterns in EQL are registered in the Esper engine and when an event arrives, it is checked against all the active patterns. What happens when one or more patterns match the event? The Esper engine notifies the listeners of the event's matching patterns.
This mechanism is analogous to the observer design...