SpringWebFlux Mono.doOnNext metodu

Giriş

Açıklaması şöyle

Mono::doOnNext triggers when the data is emitted successfully, which means the data is available and present.

Mono::doOnSuccess triggers when the Mono completes successfully - result is either T or null, which means the processing itself successfully finished regardless the state of data and is executed although the data are not available or present but the pipeline itself succeed.

Mono::then as the end of the methods chain returns Mono<Void> on complete and error signals.

Örnek

Şöyle yaparız

Mono.just(5)
  .doOnNext(i -> logger.info(i + ""))     // <-- is called and prints '5'
  .flatMap(i -> Mono.empty())
  .doOnNext(i -> logger.info(i + ""))     // <-- is NOT called
  .doOnSuccess(i -> logger.info("Done"))  // <-- is called and prints 'Done' (i is null)
  .block();

Örnek

Elimizde şöyle bir kod olsun. service::update() çalışmaz. Çünkü o da bir Mono dönüyor ve bu dönülen Mono nesnesine subscribe olunmadı

interface Service {	
  Mono<String> create(String s);
  Mono<Void> update(String s);
}
class Foo {
  private final Service service;
	
  Mono<Void> problem() {
    return service
      .create("foo")
      .doOnNext(service::update)
      .then();
  }
}

Düzeltmek için şöyle yaparız

interface Service {	
  Mono<String> create(String s);
  Mono<Void> update(String s);
}
class Foo {
  private final Service service;
	
  Mono<Void> problem() {
    return service
      .create("foo")
      .doOnNext(foo -> service.update(foo).block())
      .then();
  }
}

Açıklaması öyle

The take away here is to only use doOn* methods for side-effects, e.g. logging, uploading metrics.