Hands-On Reactive Programming in Spring 5

Reactive SSE as a lightweight replacement for WebSockets

Along with the heavyweight WebSocket, HTML 5 introduced a new way of creating static (in this case, half-duplex) connections, where the server is capable of pushing events. This technique solves similar problems to WebSocket. For example, we may declare a Server-sent events (SSE) stream using the same annotation-based programming model, but return an infinite stream of ServerSentEvent objects instead, as shown in the following example:

@RestController                                                    // (1)@RequestMapping("/sse/stocks")                                     //class StocksController {                                           //   final Map<String, StocksService> stocksServiceMap;              //   ...                                                                   @GetMapping                                                     // (2)   public Flux<ServerSentEvent<?>> streamStocks() {                // (2.1)      return Flux                                                  //         .fromIterable(