Type specific chaining with anonymous functions

ChainingRxWithCallback.java

   Api api = new Api() {
      @Override Single<String> getKey() {
        return Single.just("apiKey");
      }
    };

    api.getKey().flatMap(new Func1<String, Single<String>>() {
      @Override public Single<String> call(String key) {
        return Single.create(new Single.OnSubscribe<String>() {
          @Override public void call(final SingleSubscriber<? super String> singleSubscriber) {
            Foo foo = new Foo();
            foo.setAwesomeCallback(new AwesomeCallback() {
              @Override public void onAwesomeReady(String awesome) {
                try {
                  singleSubscriber.onSuccess(awesome);
                } catch (Exception e) {
                  singleSubscriber.onError(e);
                }
              }
            });
            foo.makeAwesome();
          }
        });
      }
    }).flatMapCompletable(new Func1<String, Completable>() {
          @Override public Completable call(final String string) {
            return Completable.create(new Completable.CompletableOnSubscribe() {
              @Override public void call(Completable.CompletableSubscriber completableSubscriber) {
                try {
                  Test.this.sendAwesome(string);
                  completableSubscriber.onCompleted();
                } catch (Exception e) {
                  completableSubscriber.onError(e);
                }
              }
            });
          }
        })
 .subscribe(new Action0() {
      @Override public void call() {
        Test.this.handleAwesomeSent();
      }
    }, new Action1<Throwable>() {
      @Override public void call(Throwable throwable) {
      }
    });

See: Stack overflow question
and: RxJava related issue
and: RxJava issued I raised about this

Todo: Find out why the two flatMapCompletable is required via new Func1<Single<String>, Completable> ... new Func1<String, Completable> instead of directly to new Func1<String, Completable>

Result: Jake Wharton's answer of Single<Single<String>> and flatMap