src/main/java/io/reactivex/Observable.java
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public final Observable<T> onExceptionResumeNext(final ObservableSource<? extends T> next) {
        ObjectHelper.requireNonNull(next, "next is null");
        return RxJavaPlugins.onAssembly(new ObservableOnErrorNext<T>(this, Functions.justFunction(next), true));
    }
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public final Observable<T> onExceptionResumeNext(final ObservableSource<? extends T> next) {
        ObjectHelper.requireNonNull(next, "next is null");
        return RxJavaPlugins.onAssembly(new ObservableOnErrorNext<T>(this, Functions.justFunction(next), true));
    }
Instructs an ObservableSource to pass control to another ObservableSource rather than invoking
{@link Observer#onError onError} if it encounters an {@link java.lang.Exception}.
<p>
This differs from {@link #onErrorResumeNext} in that this one does not handle {@link java.lang.Throwable}
or {@link java.lang.Error} but lets those continue through.
<p>
<img width="640" height="310" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/onExceptionResumeNextViaObservableSource.png" alt="">
<p>
By default, when an ObservableSource encounters an exception that prevents it from emitting the expected item
to its {@link Observer}, the ObservableSource invokes its Observer's {@code onError} method, and then quits
without invoking any more of its Observer's methods. The {@code onExceptionResumeNext} method changes
this behavior. If you pass another ObservableSource ({@code resumeSequence}) to an ObservableSource's
{@code onExceptionResumeNext} method, if the original ObservableSource encounters an exception, instead of
invoking its Observer's {@code onError} method, it will instead relinquish control to
{@code resumeSequence} which will invoke the Observer's {@link Observer#onNext onNext} method if it is
able to do so. In such a case, because no ObservableSource necessarily invokes {@code onError}, the Observer
may never know that an exception happened.
<p>
You can use this to prevent exceptions from propagating or to supply fallback data should exceptions be
encountered.
<dl>
<dt><b>Scheduler:</b></dt>
<dd>{@code onExceptionResumeNext} does not operate by default on a particular {@link Scheduler}.</dd>
</dl>

@param next
the next ObservableSource that will take over if the source ObservableSource encounters
an exception
@return the original ObservableSource, with appropriately modified behavior
@see <a href="http://reactivex.io/documentation/operators/catch.html">ReactiveX operators documentation: Catch</a>