src/main/java/io/reactivex/Flowable.java
@CheckReturnValue
    @BackpressureSupport(BackpressureKind.PASS_THROUGH)
    @SchedulerSupport(SchedulerSupport.NONE)
    public final Flowable<T> doOnNext(Consumer<? super T> onNext) {
        return doOnEach(onNext, Functions.emptyConsumer(),
                Functions.EMPTY_ACTION, Functions.EMPTY_ACTION);
    }
@CheckReturnValue
    @BackpressureSupport(BackpressureKind.PASS_THROUGH)
    @SchedulerSupport(SchedulerSupport.NONE)
    public final Flowable<T> doOnNext(Consumer<? super T> onNext) {
        return doOnEach(onNext, Functions.emptyConsumer(),
                Functions.EMPTY_ACTION, Functions.EMPTY_ACTION);
    }
@ CheckReturnValue @ BackpressureSupport ( BackpressureKind . PASS_THROUGH ) @ SchedulerSupport ( SchedulerSupport . NONE ) public final Flowable < T > doOnNext ( Consumer < ? super T > onNext ) { return doOnEach ( onNext , Functions . emptyConsumer ( ) , Functions . EMPTY_ACTION , Functions . EMPTY_ACTION ) ; }
Modifies the source Publisher so that it invokes an action when it calls {@code onNext}.
<p>
<img width="640" height="310" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/doOnNext.png" alt="">
<dl>
<dt><b>Backpressure:</b></dt>
<dd>The operator doesn't interfere with backpressure which is determined by the source {@code Publisher}'s
backpressure behavior.</dd>
<dt><b>Scheduler:</b></dt>
<dd>{@code doOnNext} does not operate by default on a particular {@link Scheduler}.</dd>
</dl>

@param onNext
the action to invoke when the source Publisher calls {@code onNext}
@return the source Publisher with the side-effecting behavior applied
@see <a href="http://reactivex.io/documentation/operators/do.html">ReactiveX operators documentation: Do</a>
Modifies the source Publisher so that it invokes an action when it calls { @code onNext } . <p > <img width = 640 height = 310 src = https : // raw . github . com / wiki / ReactiveX / RxJava / images / rx - operators / doOnNext . png alt = > <dl > <dt > <b > Backpressure : < / b > < / dt > <dd > The operator doesn t interfere with backpressure which is determined by the source { @code Publisher } s backpressure behavior . < / dd > <dt > <b > Scheduler : < / b > < / dt > <dd > { @code doOnNext } does not operate by default on a particular { @link Scheduler } . < / dd > < / dl >