net.engio:mbassador (maven):  Mbassador is a fast and flexible event bus system following the publish subscribe pattern. It is designed for ease of use and aims to be feature rich and extensible while preserving resource efficiency and performance. It provides non-blocking iterators and minimal write contention with low memory footprint. Some features: declarative handler definition via annotations, sync and/or async event delivery, weak or strong references, configurable event filters, 
Keywords: concurrent-programming|event-driven|eventbus|java|jvm