事件监听映射的上下文。

Defines and serves as a place holder for event listener mappings and configuration as needed by the engine to process the events and delegate to appropriate listeners. A context is a typical web application will hold the actual event-listener wiring that will be loaded ONCE and only ONCE, that is when an engine is started by a driver and will be cleared out when the engine stops. In a typical application it is advisable to use context in conjunction with the engine so as to allow maximum performance leverage. In future context will also support: * Automated or manual flushes. * First level caching of processed results for each event.