Is there a way to print out the chain of all operations in a Flux? - spring

Question

Given a Flux or a Mono from project reactor is a there a way to get the Flux or Mono to print out what the operator chain looks like. For example given the code below.
Fulx flux = Flux.just("a","b","c")
.map( v -> v.toUpperCase())
.log();
Is there some way to get the flux to print out a list of all the operators that are chained inside in the processing pipeline? Some nice ascii formatted text or a marble diagram?
printTheFlux(flux) should make a nice printout that show the structure of all the operators from the example above. I am not expecting to produce the code in the lambda's just a way to see what operators are chained together.

Answer 1

There is partial building blocks for doing this with the Scannable interface:
public String textRepresentation(Flux<?> flux) {
Scannable sc = Scannable.from(flux);
//scan the last operator in the chain and ask if it knows its parents
List<String> names = sc.parents().map(Scannable::operatorName)
.collect(Collectors.toList());
//as it traverses the chain from bottom to top, we need to reverse the order
Collections.reverse(names);
//need to also add the last operator
names.add(sc.operatorName());
return names.toString();
}
#Test
public void textRepresentationTest() {
Flux flux = Flux.just("a","b","c")
.map( v -> v.toUpperCase())
.log();
System.out.println(textRepresentation(flux));
}
Prints
[map, log]
Not all operators fully support it though (as you can see, the just source doesn't for instance).

Answer 2

Nice suggestion!
However, waiting for it, we can just have something like :
Disposable flux = Flux.just("a", "b", "c")
.map(String::toUpperCase)
.doOnNext(FluxUtil::print)
.subscribe();
Where FluxUtil::print is just a static method that you can write with different ways.
Here is the complete code works for me:
public class FluxUtil {
private static String s = "";
public static void main(String[] args) {
Disposable flux = Flux.just("a", "b", "c")
.map(String::toUpperCase)
.doOnNext(FluxUtil::print)
.subscribe();
}
private static Object print(Object o) {
s = !s.isEmpty() ? s.concat("->") : s;
s = s.concat(o.toString());
System.out.println(s);
return o;
}
}