Doc: @Async in an Interceptor postHandle() doesn't work [SPR-16092]

[spring-projects-issues]

Pawan Kumar opened SPR-16092 and commented

If you use a @Async("yourExecutorBeanName") in a method called by an interceptor's postHandle method (whether same class or different class), the Async nature doesn't come into picture, nor does Spring complain for a wrong bean type if doesn't exist by name of "yourExecutorBeanName".

public class EventHandlerInterceptor extends HandlerInterceptorAdapter {

    @Override
    public void postHandle(final HttpServletRequest request, final HttpServletResponse response, final Object handler, final ModelAndView modelAndView) throws Exception {
      //some custom logic
      publishSomeEvent(someRequestObj);
    }

    @Async("eventHandlerExecutor")
    public void publishSomeEvent(Request someRequestObj) {
        logger.info("Inside EventHandlerInterceptor - trying for Async.. doesn't work");
        //do something Async.
    }
}

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:task="http://www.springframework.org/schema/task"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.0.xsd
        					http://www.springframework.org/schema/task http://www.springframework.org/schema/task/spring-task-4.0.xsd">

    <!--Default Executor and Schedulers to pick-->
    <task:annotation-driven executor="eventHandlerExecutor"/>
    <task:executor id="eventHandlerExecutor" pool-size="30-40" queue-capacity="40"/><!--Not working inside Interceptor-->

</beans>

---

Backported to: 4.3.13

[spring-projects-issues]

Juergen Hoeller commented

I'm afraid this is by design: With @EnableAsync and <task:annotation-driven>, the default is proxy-based interception which only actually works when a method call comes in through the proxy: So in your scenario, you'd have to factor out the publishSomeEvent method onto a separate delegate bean which can get independently proxied, with EventHandlerInterceptor injecting a reference to that bean (receiving a proxy) and calling publishSomeEvent through it.

Alternatively, you could also do @EnableAsync(mode=ASPECTJ) and enforce AspectJ-based weaving which allows for intercepting calls within a given object as well, not dealing with a separate proxy. However, this requires a compile-time weaving or load-time weaving setup which seems overkill for your scenario. I'd rather factor out the delegate there, letting a standard proxy arrangements do the job.

That said, we should document this rather common pitfall more clearly. I'm therefore turning this issue into a documentation task.

[spring-projects-issues]

Pawan Kumar commented

Thanks a lot @Juergen. I had indeed tried using a separate @Component bean which had a method doSomethingAsync() and was calling it from EventHandlerInterceptor through @Autowire but it now looks like there was an error in my setup (project re-build most likely) earlier which was preventing the Async to happen. I had tried it multiple times and everything looked right for the setup and should've worked, hence I raised the issue here, rather than SO.
Nevertheless it works now and what you said will indeed work through a proxy. I am ok for the Spring team to resolve this issue and perhaps open a new one for the documentation.
Thanks.

[spring-projects-issues]

Juergen Hoeller commented

Let's simply repurpose this issue for the documentation work: I've added corresponding notes to the javadoc of @EnableAsync, @EnableCaching and @EnableTransactionManagement, as well to the corresponding sections in the reference documentation.

[spring-projects-issues]

Pawan Kumar commented

Sure.