Adobe. Midp. Joshuabloch. Polyforms. Esper: Event Stream Processing and Correlation. Published on ONJava.com ( See this if you're having trouble printing code examples by Thomas Bernhardt and Alexandre Vasseur 03/08/2007 Esper is an Event Stream Processing (ESP) and event correlation engine (CEP, Complex Event Processing).
Targeted to real-time Event Driven Architectures (EDA), Esper is capable of triggering custom actions written as Plain Old Java Objects (POJO) when event conditions occur among event streams. It is designed for high-volume event correlation where millions of events coming in would make it impossible to store them all to later query them using classical database architecture.