RxFlatMapAndFilter.java

/*    
* First of all we are getting my friends list from
* server, then by using flatMap we are emitting users
* one by one and then after applying filter we are
* returning only those who are following me one by one.
*/

/*
* This observable return the list of User who are my friends
*/    
private Observable<List<User>> getAllMyFriendsObservable() {
   return RxAndroidNetworking.get("https://fierce-cove-29863.herokuapp.com/getAllFriends/{userId}")
           .addPathParameter("userId", "1")
           .build()
           .getObjectListObservable(User.class);
}

/*
* This method does all
*/       
public void flatMapAndFilter() {
   getAllMyFriendsObservable()
           .flatMap(new Func1<List<User>, Observable<User>>() { // flatMap - to return users one by one
               @Override
               public Observable<User> call(List<User> usersList) {
                   return Observable.from(usersList); // returning(emitting) user one by one from usersList.
               }
           })
           .filter(new Func1<User, Boolean>() { // filter operator
               @Override
               public Boolean call(User user) {
                   // filtering user who follows me.
                   return user.isFollowing;
               }
           })
           .subscribeOn(Schedulers.io())
           .observeOn(AndroidSchedulers.mainThread())
           .subscribe(new Observer<User>() {
               @Override
               public void onCompleted() {
                   // do anything onComplete
               }

               @Override
               public void onError(Throwable e) {
                   // handle error
               }

               @Override
               public void onNext(User user) {
                   // only the user who is following me comes here one by one
               }
           });
}