Creating a Spring Reactive controller is very similar to creating a Spring MVC controller. The basic constructs are the same: @RestController and the different @RequestMapping annotations. The following snippet shows a simple reactive controller named StockPriceEventController:

    @RestController
    public class StockPriceEventController {

        @GetMapping("/stocks/price/{stockCode}")
        Flux < String > retrieveStockPriceHardcoded
                                  (@PathVariable("stockCode") String stockCode) {
            return Flux.interval(Duration.ofSeconds(5))
                       .map(l -> getCurrentDate() + " : " 
                              + getRandomNumber(100, 125))
                       .log();
        }

        private String getCurrentDate() {
            return (new Date()).toString();
        }

        private int getRandomNumber(int min, int max) {
            return ThreadLocalRandom.current().nextInt(min, max + 1);
        }

    }

A few important things to note are as follows:

• @RestController and @GetMapping("/stocks/price/{stockCode}"): Basic constructs are the same as Spring MVC. We are creating a mapping to the specified URI.
• Flux<String> retrieveStockPriceHardcoded(@PathVariable("stockCode") String stockCode): Flux represents a stream of 0 to n elements. The return type, Flux<String>, indicates that this method returns a stream of values representing the current price of a stock.
• Flux.interval().map(l -> getCurrentDate() + " : " + getRandomNumber(100, 125)): We are creating a hard-coded Flux returning a stream of random numbers.
• Duration.ofSeconds(5): Stream elements are returned every 5 seconds.
• Flux.<<****>>.log(): Invoking the log() method on Flux helps observe all Reactive streams signals and trace them using logger support.
• private String getCurrentDate(): Returns the current time as a string.
• private int getRandomNumber(int min, int max): Returns a random number between min and max.