如何在 Java 项目反应器中记录管道？

Question

I have started a new project that uses java reactor and spring webFLux. Recently I had to debug a production bug and It was a nightmare since they do not log anything. So, reading I found two ways to start adding logs to pipelines. One by using.log() and another one by using onErrorResume, doOnSubscribe, doOnSuccess. Do you know which one should I use? Are better ways to log pipelines?

    return repositoryName.findById(event.eventId())
        .filter(event -> event.completedDate() == null)
        .filterWhen(event ->
            externalService.getEventSummary(event.getUser().userId())
        .doOnNext(event -> log.info("Event found {} and should be marked as found", event.id()))

Answer 1

I highly recommend the Reactor doc to check what each method does https://projectreactor.io/docs/core/release/reference/

doOnNext , doOnError , doOnSuccess are highly used to execute blocking operations without side effects on the current stream. If you received a Square object on your doOnNext and doOnError , this method would return precisely the received Square object (even if you changed its properties)

doOnNext to execute after the previous sequence finishes try-catch

doOnError the subsequent execution if an exception was thrown (and there's no other exception handler on stream)

doOnSuccess is similar to a finally block from try-catch

onErrorResume is most used to handle exceptions if needed, similar to catch(Exception e), but it will return a new object

As you can see, it's okay to have logs on flatMap , map , doOnNext , doOnError , or onErrorResume . The correct one to use will vary on what you need. If logging is the only thing you need, I recommend doOnNext , doOnError , or doOnFinally .

As said before, please refer to the docs too to check what each method stands for