Split a flux into two fluxes - head and tail

Question

I want to split a flux into two fluxes where the first one has the first item of the original flux and the second one will takes the rest of items.

After applying a custom transformation myLogic on each flux I want to combine them into one flux preserving the order of the original flux.

Example:

S: student
S': student after applying myLogic

Emitted flux: s1 -> s2 -> s3 -> s4
The first splited flux: s1' => myLogic
The second splited flux: s2' -> s3' -> s4' => myLogic
The combined flux: s1' -> s2' -> s3' -> s4'

Answer 1

It is enough to use standard Flux methods take and skip to seprate head and tail elements. Calling cache before that is also useful to avoid subscription duplication.

class Util {

  static <T, V> Flux<V> dualTransform(
    Flux<T> originalFlux,
    int cutpointIndex,
    Function<T, V> transformHead,
    Function<T, V> transformTail
  ) {
    var cached = originalFlux.cache();
    var head = cached.take(cutpointIndex).map(transformHead);
    var tail = cached.skip(cutpointIndex).map(transformTail);

    return Flux.concat(head, tail);
  }

  static void test() {
    var sample = Flux.just("a", "b", "c", "d");

    var result = dualTransform(
                   sample,
                   1, 
                   x -> "{" + x.toUpperCase() + "}", 
                   x -> "(" + x + ")"
                 );

    result.doOnNext(System.out::print).subscribe();

    // prints: {A}(b)(c)(d)
  }
}