The document discusses WebSocket and Server-Sent Events (SSE) for building interactive web applications. It provides an overview of WebSocket including how the handshake process works and how to implement WebSocket endpoints in Java. It also summarizes how to use the Server-Sent Events API on the client-side and how to broadcast server-sent events from the server. While WebSocket allows full-duplex communication, SSE only supports server-push but is simpler to implement since it relies on standard HTTP.