How to change execution thread in Reactor - reactive-programming

Question

#RequestMapping(value = "/try",
method = RequestMethod.GET)
#ResponseBody
public String demo(){
List<String>data=new ArrayList<>();
data.add("A1");
data.add("A2");
data.add("A3");
data.add("A4");
Flux.fromIterable(data).subscribe(s->printStatement(s));
return "done";
}
public void printStatement(String s){
long i;
for(i=0;i<1000000000;i++)
{}
LOGGER.info(s+"------"+Thread.currentThread().getId());
}
Here in the above example i was hoping that the tread id would be different(hopping asynchronouslyexecution).From log i could see that same tread is executing the entire process
Log:
2018-05-02 03:24:42.387 INFO 29144 --- [nio-8080-exec-1] c.n.p.s.p.reactorDemo : A1------26
2018-05-02 03:24:44.118 INFO 29144 --- [nio-8080-exec-1] c.n.p.s.p.reactorDemo : A2------26
2018-05-02 03:24:44.418 INFO 29144 --- [nio-8080-exec-1] c.n.p.s.p.reactorDemo : A3------26
2018-05-02 03:24:44.717 INFO 29144 --- [nio-8080-exec-1] c.n.p.s.p.reactorDemo : A4------26
How i do i make sure its executing asynchronously.

Answer 1

The execution model of Reactor is that most operators don't change the thread for you (except when time is involved). The library offers two operators that allow switching to threads, publishOn (the most common) and subscribeOn.
For example Flux.fromIterable(data).publishOn(Schedulers.newSingle("example")).subscribe(...) would be the way to go here.
Note that WebFlux's model is that it starts the processing of the chain in the Netty threads, these nio threads that you see. It is thus very important that you don't block these threads (that would prevent processing of further incoming requests entirely).
Schedulers offer factory methods for various Scheduler flavors, which is a Reactor abstraction (more or less on top of ExecutorService).