Spring WebClient is not emitting any data from request - spring-webflux

Question

This is the content type of the request
I use spring boot and this code to redirect the stream from the web server to the browser.
public Flux<String> getDataStream(String configType, String configId, String user){
Flux<String> response = null;
Optional<String> url = getLogURL(configId);
if(url.isPresent()){
logger.info("#WebClient initiation");
WebClient webClient = WebClient.create();
response = webClient.get()
.uri(url.get())
.accept(MediaType.ALL)
.retrieve()
.bodyToFlux(String.class);
}
logger.info("#WebClient response");
return response;
}
After making the request, I can see #WebClient initiation and #WebClient response in a log file.
This is the client-side JavaScript code statement, that hits the above code getDataStream()
let eventSource = new EventSource(STREAM_URL);
But it doesn't get any response from the server. I couldn't figure out what I am missing. The URL that getDataStream()->WebClient hits, confirmed to produces output.

Answer 1

There are several options to stream data from the server using WebFlux:
Server-sent events pushing individual events (media type: text/event-stream)
Streaming events separated by newlines (media type: application/x-ndjson)
If you need plain text content - use text/event-stream. Check WebFlux async responses from controllers for a complete example.
To see response results you need to log it as a part of the reactive flow. Also, there is no null in reactive and you need to return Flux.empty() instead.
#GetMapping(produces = TEXT_EVENT_STREAM_VALUE)
public Flux<String> getDataStream(String configType, String configId, String user){
Optional<String> url = getLogURL(configId);
if (url.isEmpty()) {
return Flux.empty();
}
log.info("#WebClient initiation");
WebClient webClient = WebClient.create();
return webClient.get()
.uri(url.get())
.accept(MediaType.ALL)
.retrieve()
.bodyToFlux(String.class)
.doOnSubscribe(s -> log.info("#WebClient request"))
.doOnNext(rec -> log.info("#WebClient response record: {}", rec));
}