how to get the object returned from joinPoint.proceed() with Spring AOP and WebFlux

2
votes

I have a simple aspect (see below) with @Around annotation. This aspect works when the the application don't use reactive paradigm. But when the application returns Mono or Flux doesn't works properly.

I need to get the object returned from the method to generate a JSON object to use as log, generate events, etc.

Here is my code that works in a non reactive classes:

@Around("@annotation(simpleEvent)")
public Object logExecutionTime(ProceedingJoinPoint joinPoint, SimpleEvent simpleEvent) throws Throwable {
    final long start = System.currentTimeMillis();
    Object proceed = null;
    try {
        proceed = joinPoint.proceed();
        // here in the real life the object that transformed in json to do others actions
        System.out.println(proceed);
        final long executionTime = System.currentTimeMillis() - start;
        System.out.println(joinPoint.getSignature() + " executed in " + executionTime + "ms");
        return proceed;
    } catch (Exception e) {
        e.printStackTrace(); 
    }
    return proceed;
}

How to get the object returned from joinPoint.proceed() when is Mono or Flux?

Thanks in advance.

2
javaspringspring-aopspring-webfluxproject-reactor
A Flux or a Mono represent a deferred computation. Such a method usually immediately returns, with an "inert" Mono which will be triggered once something calls one of its subscribe methods, so that kind of aspect isn't adapted anymore. – Simon Baslé
Hi Simon, first of all, thanks for your answer. Sorry but I am new with Spring reactive. In this case it's possible to subscribe to receive the events returned from Flux or Mono too? I use this aspect to throw a business event. There are another approach with reactive style? If yes you can point me in a correct way? Thanks. – Maicon Luz
You could change the returned Mono and add a side effect to it. Look at the doOn* methods, which don't change the type of the Mono but add behavior triggered by various events. The business logic shod be non blocking – Simon Baslé

2 Answers

3
votes

you can do like this, same when proceed return a Mono

@Around("somePointCut()")
public Object aspectForSomething(ProceedingJoinPoint point) throws Throwable {
    Flux flux = (Flux) point.proceed();
    return flux
            .doOnNext(obj -> {
                log.error("just take a look: " + obj);
            })
            .map(obj -> {
                if (obj instanceof SomeBo) {
                    SomeBo bo = (SomeBo) obj;
                    bo.setName("do some modification");
                    return bo;
                } else {
                    return obj;
                }
            });
}
2
votes

The key is to wrap the joinPoint.proceed() in Mono and access it in a reactive chain.

@Around("@annotation(simpleEvent)")
public Object logExecutionTime(ProceedingJoinPoint joinPoint, SimpleEvent simpleEvent) throws Throwable {
    final long start = System.currentTimeMillis();
    Mono proceed = null;
    try {
        proceed = (Mono) joinPoint.proceed();

        return proceed.doOnNext(response -> {
            final long executionTime = System.currentTimeMillis() - start;
            // here you can access the response object and do your actions
            System.out.println(response);
            System.out.println(joinPoint.getSignature() + " executed in " + executionTime + "ms");
        });
    } catch (Exception e) {
        e.printStackTrace();
    }
    return proceed;
}