reactor-core/src/main/java/reactor/core/publisher/Flux.java
public final Flux<T> log(@Nullable String category,
			Level level,
			boolean showOperatorLine,
			SignalType... options) {
		SignalLogger<T> log = new SignalLogger<>(this, category, level,
				showOperatorLine, options);

		if (this instanceof Fuseable) {
			return onAssembly(new FluxLogFuseable<>(this, log));
		}
		return onAssembly(new FluxLog<>(this, log));
	}
public final Flux<T> log(@Nullable String category,
			Level level,
			boolean showOperatorLine,
			SignalType... options) {
		SignalLogger<T> log = new SignalLogger<>(this, category, level,
				showOperatorLine, options);

		if (this instanceof Fuseable) {
			return onAssembly(new FluxLogFuseable<>(this, log));
		}
		return onAssembly(new FluxLog<>(this, log));
	}
Observe Reactive Streams signals matching the passed filter {@code options} and
trace them using {@link Logger} support. Default will use {@link Level#INFO} and
{@code java.util.logging}. If SLF4J is available, it will be used instead.
<p>
Options allow fine grained filtering of the traced signal, for instance to only
capture onNext and onError:
<pre>
flux.log("category", Level.INFO, SignalType.ON_NEXT, SignalType.ON_ERROR)
</pre>
<p>
<img class="marble" src="doc-files/marbles/logForFlux.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 be added, e.g. "reactor.Flux.Map".
@param level the {@link Level} to enforce for this tracing Flux (only FINEST, FINE,
INFO, WARNING and SEVERE are taken into account)
@param showOperatorLine capture the current stack to display operator class/line number.
@param options a vararg {@link SignalType} option to filter log messages

@return a new {@link Flux} that logs signals