Event-Driven LISTEN/NOTIFY Support in Java using PostgreSQL

PostgreSQL's LISTEN and NOTIFY commands enable asynchronous communication between database server and clients, creating a simple messaging system. The LISTEN command registers interest in receiving events on specific channels, while NOTIFY broadcasts messages to all listeners. Java applications can raise notifications using standard JDBC with either NOTIFY commands or pg_notify() function. Listening for notifications requires driver-specific functionality - the official PostgreSQL JDBC driver requires polling with getNotifications(), while PGJDBC-NG provides callback-based listeners for more efficient event handling. This mechanism supports real-time dashboards, cache invalidation, and data auditing use cases.