execute 2 Mono sequentialy not supporte blocking

Question

i have the two bellow functions

Mono<Void> messageEvent(MessageEvent messageEvent);
Mono<Victim> getPersonById(String personId);

i want when the function messageEvent is executed successfully i executethe getPersonById function, and the return of the getPersonById function is saved in the database

i tried like below

    spi.messageEvent(message).doOnSuccess(it -> {
        spi.getPersonById(evt.getVictimId()).doOnSuccess(victim -> {
            repository.save(victim);
        }).block();
    }).block();

but i have this error

2023-03-09 21:56:20.191 ERROR 21080 --- [nister-group]-0] c.s.e.v.s.q.i : Exception in on() with cause = 'NULL' and exception = 'block()/blockFirst()/blockLast() are blocking, which is not supported in thread reactor-http-nio-2' java.lang.IllegalStateException: block()/blockFirst()/blockLast() are blocking, which is not supported in thread reactor-http-nio-2 at reactor.core.publisher.BlockingSingleSubscriber.blockingGet(BlockingSingleSubscriber.java:83

)

Answer 1

You need this operator from Mono:

/**
 * Let this {@link Mono} complete then play another Mono.
 * <p>
 * In other words ignore element from this {@link Mono} and transform its completion signal into the
 * emission and completion signal of a provided {@code Mono<V>}. Error signal is
 * replayed in the resulting {@code Mono<V>}.
 *
 * <p>
 * <img class="marble" src="doc-files/marbles/thenWithMonoForMono.svg" alt="">
 *
 * <p><strong>Discard Support:</strong> This operator discards the element from the source.
 *
 * @param other a {@link Mono} to emit from after termination
 * @param <V> the element type of the supplied Mono
 *
 * @return a new {@link Mono} that emits from the supplied {@link Mono}
 */
public final <V> Mono<V> then(Mono<V> other) {

So, in your code it probably could be like this:

 return spi.messageEvent(message)
     .then(spi.getPersonById(evt.getVictimId()))
     .map(repository::save);

And yes: don't use block() in a Reactor Http thread.