About side effect
Side effect is the code that to monitor particular signals which flow in the operator chain. Following is available operator and please check the javadoc on when these functions will be called.
- doOnSubscribe()
- doOnNext()
- doOnError()
- doOnComplete()
- doOnTerminate()
- doAfterTerminate()
- doOnRequest()
- doOnCancel()
- doOnEach()
- doFirst()
- doFinally()
Direction of signal flow
In rare situation, 2 or more of the same operator will be chain together. There is a problem that will operator will be called first. This depends on the direction of the signal flow. On example below
package example;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import reactor.core.publisher.Flux;
public class SignalFlow {
private static final Logger LOGGER = LoggerFactory.getLogger(SignalFlow.class);
public static void main(String[] args) {
Flux<Integer> f1 = Flux.just(1, 2, 3, 4)
.doOnNext(v -> LOGGER.info("doOnNext (1): {}", v)) // doOnNext (1)
.doOnNext(v -> LOGGER.info("doOnNext (2): {}", v)) // doOnNext (2)
.map(v -> v * 2);
f1.subscribe();
Flux<Integer> f2 = Flux.just(1, 2, 3, 4)
.doOnRequest(v -> LOGGER.info("doOnRequest (1): {}", v)) // doOnRequest (1)
.doOnRequest(v -> LOGGER.info("doOnRequest (2): {}", v)) // doOnRequest (2)
.map(v -> v * 2);
f2.subscribe();
}
}
And the result is
15:44:46.451 [main] INFO example.SignalFlow -- doOnNext (1): 1
15:44:46.451 [main] INFO example.SignalFlow -- doOnNext (2): 1
15:44:46.451 [main] INFO example.SignalFlow -- doOnNext (1): 2
15:44:46.451 [main] INFO example.SignalFlow -- doOnNext (2): 2
15:44:46.451 [main] INFO example.SignalFlow -- doOnNext (1): 3
15:44:46.451 [main] INFO example.SignalFlow -- doOnNext (2): 3
15:44:46.451 [main] INFO example.SignalFlow -- doOnNext (1): 4
15:44:46.451 [main] INFO example.SignalFlow -- doOnNext (2): 4
15:44:46.451 [main] INFO example.SignalFlow -- doOnRequest (2): 9223372036854775807
15:44:46.451 [main] INFO example.SignalFlow -- doOnRequest (1): 9223372036854775807
On operator doOnNext(), the flow is from Publisher to Subscriber, so the result is "doOnNext (1)" and then "doOnNext (2)". But on operator doOnRequest(), the flow is in reverse direction. So "doOnRequest (2)" will be shown first. Following is the summary
| Function | Direction of signal flow |
|---|---|
| doOnSubscribe() | Publisher to Subscriber |
| doOnNext() | Publisher to Subscriber |
| doOnError() | Publisher to Subscriber |
| doOnComplete() | Publisher to Subscriber |
| doOnTerminate() | Publisher to Subscriber |
| doAfterTerminate() | Subscriber to Publisher |
| doOnRequest() | Subscriber to Publisher |
| doOnCancel() | Subscriber to Publisher |
| doOnEach() | Publisher to Subscriber |
| doFirst() | Subscriber to Publisher |
| doFinally() | Subscriber to Publisher |
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