CODEWITHSUNDEEP
springreactive-programmingspring-webflux
DarkVaderM
DarkVaderM

Reputation: 129

At what point does the subscription take place? (spring webflux)

At what point does the spring webflux do the subscription? Everywhere I have read that there must be a subscription otherwise no change happens. In my short time with Spring Webflux, I have never seen a subscribe() neither in the controller or services.

My doubt is also when using flatMap(), map(),... etc.. at what point does the subscription take place?

What I have read does not really resolve my doubts.

public Flux method(){
    ....
    myFlux.flatMap(data -> {
          ....

    }).flatMap(e -> { .... });
}

I know this is an asynchronous issue, but each flatMap runs at the same time?...and so sometimes some data I have noticed is null.

Upvotes: 6

Views: 8958

Answers (3)

João Dias
João Dias

Reputation: 17460

The answer is: it depends.

For example, if this is a Spring Controller method, then it is the framework itself that subscribes to the Mono or Flux.

If it is a method that is triggered from time to time by a Scheduler, then you must explicitly subscribe to the Mono or Flux, otherwise, no processing will take place.

This means that if your application only exposes a REST API and no processing need to be triggered in any other way, then it is very likely that you will never need to explicitly subscribe to a Mono or Flux because Spring will take care of that by you.

Upvotes: 0

Martin Tarjányi
Martin Tarjányi

Reputation: 9947

It's the framework (spring-webflux) that subscribes to the returned Mono or Flux. For example if you use Netty (that's the default), then subscription happens here based on my debugging: https://github.com/reactor/reactor-netty/blob/db27625064fc78f8374c1ef0af3160ec3ae979f4/reactor-netty-http/src/main/java/reactor/netty/http/server/HttpServer.java#L962

Also, this article might be of help to understand what happens when: https://spring.io/blog/2019/03/06/flight-of-the-flux-1-assembly-vs-subscription

Upvotes: 7

seoboss
seoboss

Reputation: 126

You need to call a .subscribe() or block() function after your flatmap. Here's an example.

Assuming that myFlux is of type Flux, the following will execute the subscription based on the example above myFlux.subscribe(System.out::println);

Here's an explanation on a separate StackOverflow thread.

But in your method function, you are returning a Flux object - so it's up to the consumer of the method() function how it wants to subscribe to the Flux. You shouldn't be trying to subscribe to the Flux from within

Upvotes: 0

Related Questions