Why is this an issue?

Spring provides the @EventListener annotation as a simpler alternative to implementing the ApplicationListener interface for handling events. The @EventListener annotation registers a method as an event handler. This allows to skip the implementation of the ApplicationListener interface, making it easier to handle events.

The @EventListener annotation can only be used on methods that have at most one parameter, which should be the specific event that we want to handle. To listen to several types of events, use the classes argument of the @EventListener annotation.

This rule raises an issue on all methods annotated with @EventListener that have more than one parameter.

How to fix it

Code examples

Noncompliant code example

@EventListener
void handleEvent(CustomerEvent customerEvent, ExceptionalEvent exceptionalEvent) { // Non compliant, this will cause a runtime error
    //... some event handling
}

Compliant solution

@EventListener(classes = {CustomerEvent.class, ExceptionalEvent.class})
void handleEvent(ApplicationEvent event) { // Only one parameter, of the super type `ApplicationEvent`
    //... some event handling
}

Resources

Documentation

Spring API - @EventListener