DoOnEmptyOperator.java

import rx.Observable.Operator;
import rx.Subscriber;
import rx.functions.Action0;

public final class DoOnEmptyOperator<T> implements Operator<T, T> {
    private final Action0 empty;

    public DoOnEmptyOperator(Action0 empty) {
        this.empty = empty;
    }

    @Override
    public Subscriber<? super T> call(final Subscriber<? super T> child) {
        return new Subscriber<T>(child) {
            boolean hasValue;

            @Override
            public void onNext(T t) {
                hasValue = true;
                child.onNext(t);
            }

            @Override
            public void onError(Throwable e) {
                child.onError(e);
            }

            @Override
            public void onCompleted() {
                if (!hasValue) {
                    try {
                        empty.call();
                    } catch (Throwable e) {
                        child.onError(e);
                        return;
                    }
                }
                child.onCompleted();
            }

        };
    }

}