spring webflux returns application/stream+json

order

This paper mainly studies the example of spring webflux returning application/stream+json

maven

		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-webflux</artifactId>
		</dependency>

controller

    /**
     * curl -i localhost:8080/stream
     * @return
     */
    @GetMapping(value = "/stream",produces = MediaType.APPLICATION_STREAM_JSON_VALUE)
    public Flux<Price> priceStream(){
        return Flux.interval(Duration.ofMillis(500))
                .map(l -> new Price(System.currentTimeMillis(),ThreadLocalRandom.current().nextInt(100, 125)))
                .log();
    }

Notice here that produces = MediaType.APPLICATION_STREAM_JSON_VALUE If it is not application/stream+json, the caller cannot scroll to get the result, and will be blocked waiting for the end of the data stream or timeout.

output

Background output

2018-02-08 21:36:49.701  INFO 1270 --- [ctor-http-nio-2] reactor.Flux.Map.1                       : onSubscribe(FluxMap.MapSubscriber)
2018-02-08 21:36:49.702  INFO 1270 --- [ctor-http-nio-2] reactor.Flux.Map.1                       : request(1)
2018-02-08 21:36:50.208  INFO 1270 --- [     parallel-2] reactor.Flux.Map.1                       : onNext(Price(timestamp=1518097010208, value=120.0))
2018-02-08 21:36:50.229  INFO 1270 --- [ctor-http-nio-2] reactor.Flux.Map.1                       : request(31)
2018-02-08 21:36:50.708  INFO 1270 --- [     parallel-2] reactor.Flux.Map.1                       : onNext(Price(timestamp=1518097010708, value=124.0))
2018-02-08 21:36:51.208  INFO 1270 --- [     parallel-2] reactor.Flux.Map.1                       : onNext(Price(timestamp=1518097011208, value=119.0))
2018-02-08 21:36:51.707  INFO 1270 --- [     parallel-2] reactor.Flux.Map.1                       : onNext(Price(timestamp=1518097011707, value=120.0))
2018-02-08 21:36:52.207  INFO 1270 --- [     parallel-2] reactor.Flux.Map.1                       : onNext(Price(timestamp=1518097012207, value=109.0))
2018-02-08 21:36:52.707  INFO 1270 --- [     parallel-2] reactor.Flux.Map.1                       : onNext(Price(timestamp=1518097012707, value=101.0))
2018-02-08 21:36:53.208  INFO 1270 --- [     parallel-2] reactor.Flux.Map.1                       : onNext(Price(timestamp=1518097013208, value=114.0))
2018-02-08 21:36:53.707  INFO 1270 --- [     parallel-2] reactor.Flux.Map.1                       : onNext(Price(timestamp=1518097013707, value=113.0))
2018-02-08 21:36:54.206  INFO 1270 --- [     parallel-2] reactor.Flux.Map.1                       : onNext(Price(timestamp=1518097014206, value=105.0))
2018-02-08 21:36:54.708  INFO 1270 --- [     parallel-2] reactor.Flux.Map.1                       : onNext(Price(timestamp=1518097014708, value=103.0))
2018-02-08 21:36:55.208  INFO 1270 --- [     parallel-2] reactor.Flux.Map.1                       : onNext(Price(timestamp=1518097015207, value=123.0))
2018-02-08 21:36:55.212  INFO 1270 --- [ctor-http-nio-2] reactor.Flux.Map.1                       : cancel()

Caller output

curl -i localhost:8080/stream
HTTP/1.1 200 OK
transfer-encoding: chunked
Content-Type: application/stream+json;charset=UTF-8

{"timestamp":1518097010208,"value":120.0}
{"timestamp":1518097010708,"value":124.0}
{"timestamp":1518097011208,"value":119.0}
{"timestamp":1518097011707,"value":120.0}
{"timestamp":1518097012207,"value":109.0}
{"timestamp":1518097012707,"value":101.0}
{"timestamp":1518097013208,"value":114.0}
{"timestamp":1518097013707,"value":113.0}
{"timestamp":1518097014206,"value":105.0}
^C

You can see that the transfer-encoding returned is chunked due to the use of application/stream+json, so the caller can achieve scrolling output.

paging

After using webflux, you may be curious about previous paging calls. reactive-streams use data as data streams, so spring data reactive does not support returning Page, but calling parameters can pass Pageable parameters.

public interface StocDao extends ReactiveCrudRepository<Stock, String> {

    Flux<Stock> findByName(String name,Pageable pageable);
}

Note that Flux < Stock > is returned here, not Page < Stock > That's equivalent to losing total count.

Summary

For the flow data of Flux returned by webflux, we need to cooperate with the return of MediaType.APPLICATION_STREAM_JSON_VALUE, and the caller also needs to be able to support this media type (WebClient support), so as to enable the effect of reactive streams.

doc

Posted by jason_kraft on Thu, 07 Feb 2019 14:18:17 -0800

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