reactor-core/src/main/java/reactor/core/publisher/Mono.java
public final Mono<T> log(@Nullable String category) {
		return log(category, Level.INFO);
	}
public final Mono<T> log(@Nullable String category) {
		return log(category, Level.INFO);
	}
Observe all Reactive Streams signals and use {@link Logger} support to handle trace implementation. Default will
use {@link Level#INFO} and java.util.logging. If SLF4J is available, it will be used instead.

<p>
<img class="marble" src="doc-files/marbles/logForMono.svg" alt="">

@param category to be mapped into logger configuration (e.g. org.springframework
.reactor). If category ends with "." like "reactor.", a generated operator
suffix will complete, e.g. "reactor.Flux.Map".

@return a new {@link Mono}